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Paclitaxel Drug-Drug Interactions in the Military Health System
Background
Paclitaxel was first derived from the bark of the yew tree (Taxus brevifolia). It was discovered as part of a National Cancer Institute program screen of plants and natural products with putative anticancer activity during the 1960s.1-9 Paclitaxel works by suppressing spindle microtube dynamics, which results in the blockage of the metaphase-anaphase transitions, inhibition of mitosis, and induction of apoptosis in a broad spectrum of cancer cells. Paclitaxel also displayed additional anticancer activities, including the suppression of cell proliferation and antiangiogenic effects. However, since the growth of normal body cells may also be affected, other adverse effects (AEs) will also occur.8-18
Two different chemotherapy drugs contain paclitaxel—paclitaxel and nab-paclitaxel—and the US Food and Drug Administration (FDA) recognizes them as separate entities.19-21 Taxol (paclitaxel) was approved by the FDA in 1992 for treating advanced ovarian cancer.20 It has since been approved for the treatment of metastatic breast cancer, AIDS-related Kaposi sarcoma (as an orphan drug), non-small cell lung cancer (NSCLC), and cervical cancers (in combination withbevacizumab) in 1994, 1997, 1999, and 2014, respectively.21 Since 2002, a generic version of Taxol, known as paclitaxel injectable, has been FDA-approved from different manufacturers. According to the National Cancer Institute, a combination of carboplatin and Taxol is approved to treat carcinoma of unknown primary, cervical, endometrial, NSCLC, ovarian, and thymoma cancers.19 Abraxane (nab-paclitaxel) was FDA-approved to treat metastatic breast cancer in 2005. It was later approved for first-line treatment of advanced NSCLC and late-stage pancreatic cancer in 2012 and 2013, respectively. In 2018 and 2020, both Taxol and Abraxane were approved for first-line treatment of metastatic squamous cell NSCLC in combination with carboplatin and pembrolizumab and metastatic triple-negative breast cancer in combination with pembrolizumab, respectively.22-26 In 2019, Abraxane was approved with atezolizumab to treat metastatic triple-negative breast cancer, but this approval was withdrawn in 2021. In 2022, a generic version of Abraxane, known as paclitaxel protein-bound, was released in the United States. Furthermore, paclitaxel-containing formulations also are being studied in the treatment of other types of cancer.19-32
One of the main limitations of paclitaxel is its low solubility in water, which complicates its drug supply. To distribute this hydrophobic anticancer drug efficiently, paclitaxel is formulated and administered to patients via polyethoxylated castor oil or albumin-bound (nab-paclitaxel). However, polyethoxylated castor oil induces complement activation and is the cause of common hypersensitivity reactions related to paclitaxel use.2,17,33-38 Therefore, many alternatives to polyethoxylated castor oil have been researched.
Since 2000, new paclitaxel formulations have emerged using nanomedicine techniques. The difference between these formulations is the drug vehicle. Different paclitaxel-based nanotechnological vehicles have been developed and approved, such as albumin-based nanoparticles, polymeric lipidic nanoparticles, polymeric micelles, and liposomes, with many others in clinical trial phases.3,37 Albumin-based nanoparticles have a high response rate (33%), whereas the response rate for polyethoxylated castor oil is 25% in patients with metastatic breast cancer.33,39-52 The use of paclitaxel dimer nanoparticles also has been proposed as a method for increasing drug solubility.33,53
Paclitaxel is metabolized by cytochrome P450 (CYP) isoenzymes 2C8 and 3A4. When administering paclitaxel with known inhibitors, inducers, or substrates of CYP2C8 or CYP3A4, caution is required.19-22 Regulations for CYP research were not issued until 2008, so potential interactions between paclitaxel and other drugs have not been extensively evaluated in clinical trials. A study of 12 kinase inhibitors showed strong inhibition of CYP2C8 and/or CYP3A4 pathways by these inhibitors, which could alter the ratio of paclitaxel metabolites in vivo, leading to clinically relevant changes.54 Differential metabolism has been linked to paclitaxel-induced neurotoxicity in patients with cancer.55 Nonetheless, variants in the CYP2C8, CYP3A4, CYP3A5, and ABCB1 genes do not account for significant interindividual variability in paclitaxel pharmacokinetics.56 In liver microsomes, losartan inhibited paclitaxel metabolism when used at concentrations > 50 µmol/L.57 Many drug-drug interaction (DDI) studies of CYP2C8 and CYP3A4 have shown similar results for paclitaxel.58-64
The goals of this study are to investigate prescribed drugs used with paclitaxel and determine patient outcomes through several Military Health System (MHS) databases. The investigation focused on (1) the functions of paclitaxel; (2) identifying AEs that patients experienced; (3) evaluating differences when paclitaxel is used alone vs concomitantly and between the completed vs discontinued treatment groups; (4) identifying all drugs used during paclitaxel treatment; and (5) evaluating DDIs with antidepressants (that have an FDA boxed warning and are known to have DDIs confirmed in previous publications) and other drugs.65-67
The Walter Reed National Military Medical Center in Bethesda, Maryland, institutionalreview board approved the study protocol and ensured compliance with the Health Insurance Portability and Accountability Act as an exempt protocol. The Joint Pathology Center (JPC) of the US Department of Defense (DoD) Cancer Registry Program and MHS data experts from the Comprehensive Ambulatory/Professional Encounter Record (CAPER) and the Pharmacy Data Transaction Service (PDTS) provided data for the analysis.
METHODS
The DoD Cancer Registry Program was established in 1986 and currently contains data from 1998 to 2024. CAPER and PDTS are part of the MHS Data Repository/Management Analysis and Reporting Tool database. Each observation in the CAPER record represents an ambulatory encounter at a military treatment facility (MTF). CAPER includes data from 2003 to 2024.
Each observation in the PDTS record represents a prescription filled for an MHS beneficiary at an MTF through the TRICARE mail-order program or a US retail pharmacy. Missing from this record are prescriptions filled at international civilian pharmacies and inpatient pharmacy prescriptions. The MHS Data Repository PDTS record is available from 2002 to 2024. The legacy Composite Health Care System is being replaced by GENESIS at MTFs.
Data Extraction Design
The study design involved a cross-sectional analysis. We requested data extraction for paclitaxel from 1998 to 2022. Data from the DoD Cancer Registry Program were used to identify patients who received cancer treatment. Once patients were identified, the CAPER database was searched for diagnoses to identify other health conditions, whereas the PDTS database was used to populate a list of prescription medications filled during chemotherapy treatment.
Data collected from the JPC included cancer treatment, cancer information, demographics, and physicians’ comments on AEs. Collected data from the MHS include diagnosis and filled prescription history from initiation to completion of the therapy period (or 2 years after the diagnosis date). For the analysis of the DoD Cancer Registry Program and CAPER databases, we used all collected data without excluding any. When analyzing PDTS data, we excluded patients with PDTS data but without a record of paclitaxel being filled, or medications filled outside the chemotherapy period (by evaluating the dispensed date and day of supply).
Data Extraction Analysis
The Surveillance, Epidemiology, and End Results Program Coding and Staging Manual 2016 and the International Classification of Diseases for Oncology, 3rd edition, 1st revision, were used to decode disease and cancer types.68,69 Data sorting and analysis were performed using Microsoft Excel. The percentage for the total was calculated by using the number of patients or data available within the paclitaxel groups divided by the total number of patients or data variables. The subgroup percentage was calculated by using the number of patients or data available within the subgroup divided by the total number of patients in that subgroup.
In alone vs concomitant and completed vs discontinued treatment groups, a 2-tailed, 2-sample z test was used to statistical significance (P < .05) using a statistics website.70 Concomitant was defined as paclitaxel taken with other antineoplastic agent(s) before, after, or at the same time as cancer therapy. For the retrospective data analysis, physicians’ notes with a period, comma, forward slash, semicolon, or space between medication names were interpreted as concurrent, whereas plus (+), minus/plus (-/+), or “and” between drug names that were dispensed on the same day were interpreted as combined with known common combinations: 2 drugs (DM886 paclitaxel and carboplatin and DM881-TC-1 paclitaxel and cisplatin) or 3 drugs (DM887-ACT doxorubicin, cyclophosphamide, and paclitaxel). Completed treatment was defined as paclitaxel as the last medication the patient took without recorded AEs; switching or experiencing AEs was defined as discontinued treatment.
RESULTS
The JPC provided 702 entries for 687 patients with a mean age of 56 years (range, 2 months to 88 years) who were treated with paclitaxel from March 1996 to October 2021. Fifteen patients had duplicate entries because they had multiple cancer sites or occurrences. There were 623 patients (89%) who received paclitaxel for FDA-approved indications. The most common types of cancer identified were 344 patients with breast cancer (49%), 91 patients with lung cancer (13%), 79 patients with ovarian cancer (11%), and 75 patients with endometrial cancer (11%) (Table 1). Seventy-nine patients (11%) received paclitaxel for cancers that were not for FDA-approved indications, including 19 for cancers of the fallopian tube (3%) and 17 for esophageal cancer (2%) (Table 2).
There were 477 patients (68%) aged > 50 years. A total of 304 patients (43%) had a stage III or IV cancer diagnosis and 398 (57%) had stage II or lower (combination of data for stages 0, I, and II; not applicable; and unknown) cancer diagnosis. For systemic treatment, 16 patients (2%) were treated with paclitaxel alone and 686 patients (98%) received paclitaxel concomitantly with additional chemotherapy: 59 patients (9%) in the before or after group, 410 patients (58%) had a 2-drug combination, 212 patients (30%) had a 3-drug combination, and 5 patients (1%) had a 4-drug combination. In addition, for doublet therapies, paclitaxel combined with carboplatin, trastuzumab, gemcitabine, or cisplatin had more patients (318, 58, 12, and 11, respectively) than other combinations (≤ 4 patients). For triplet therapies, paclitaxel combined withdoxorubicin plus cyclophosphamide or carboplatin plus bevacizumab had more patients (174 and 20, respectively) than other combinations, including quadruplet therapies (≤ 4 patients) (Table 3).
Patients were more likely to discontinue paclitaxel if they received concomitant treatment. None of the 16 patients receiving paclitaxel monotherapy experienced AEs, whereas 364 of 686 patients (53%) treated concomitantly discontinued (P < .001). Comparisons of 1 drug vs combination (2 to 4 drugs) and use for treating cancers that were FDA-approved indications vs off-label use were significant (P < .001), whereas comparisons of stage II or lower vs stage III and IV cancer and of those aged ≤ 50 years vs aged > 50 years were not significant (P = .50 andP = .30, respectively) (Table 4).
Among the 364 patients who had concomitant treatment and had discontinued their treatment, 332 (91%) switched treatments with no AEs documented and 32 (9%) experienced fatigue with pneumonia, mucositis, neuropathy, neurotoxicity, neutropenia, pneumonitis, allergic or hypersensitivity reaction, or an unknown AE. Patients who discontinued treatment because of unknown AEs had a physician’s note that detailed progressive disease, a significant decline in performance status, and another unknown adverse effect due to a previous sinus tract infection and infectious colitis (Table 5).
Management Analysis and Reporting Tool Database
MHS data analysts provided data on diagnoses for 639 patients among 687 submitteddiagnoses, with 294 patients completing and 345 discontinuing paclitaxel treatment. Patients in the completed treatment group had 3 to 258 unique health conditions documented, while patients in the discontinued treatment group had 4 to 181 unique health conditions documented. The MHS reported 3808 unique diagnosis conditions for the completed group and 3714 for the discontinued group (P = .02).
The mean (SD) number of diagnoses was 51 (31) for the completed and 55 (28) for the discontinued treatment groups (Figure). Among 639 patients who received paclitaxel, the top 5 diagnoses were administrative, including encounters for other administrative examinations; antineoplastic chemotherapy; administrative examination for unspecified; other specified counseling; and adjustment and management of vascular access device. The database does not differentiate between administrative and clinically significant diagnoses.
MHS data analysts provided data for 336 of 687 submitted patients who were prescribed paclitaxel; 46 patients had no PDTS data, and 305 patients had PDTS data without paclitaxel, Taxol, or Abraxane dispensed. Medications that were filled outside the chemotherapy period were removed by evaluating the dispensed date and day of supply. Among these 336 patients, 151 completed the treatment and 185 discontinued, with 14 patients experiencing documented AEs. Patients in the completed treatment group filled 9 to 56 prescriptions while patients in the discontinued treatment group filled 6 to 70 prescriptions.Patients in the discontinued group filled more prescriptions than those who completed treatment: 793 vs 591, respectively (P = .34).
The mean (SD) number of filled prescription drugs was 24 (9) for the completed and 34 (12) for the discontinued treatment group. The 5 most filled prescriptions with paclitaxel from 336 patients with PDTS data were dexamethasone (324 prescriptions with 14 recorded AEs), diphenhydramine (296 prescriptions with 12 recorded AEs), ondansetron (277 prescriptions with 11 recorded AEs), prochlorperazine (265 prescriptions with 12 recorded AEs), and sodium chloride (232 prescriptions with 11 recorded AEs).
DISCUSSION
As a retrospective review, this study is more limited in the strength of its conclusions when compared to randomized control trials. The DoD Cancer Registry Program only contains information about cancer types, stages, treatment regimens, and physicians’ notes. Therefore, noncancer drugs are based solely on the PDTS database. In most cases, physicians' notes on AEs were not detailed. There was no distinction between initial vs later lines of therapy and dosage reductions. The change in status or appearance of a new medical condition did not indicate whether paclitaxel caused the changes to develop or directly worsen a pre-existing condition. The PDTS records prescriptions filled, but that may not reflect patients taking prescriptions.
Paclitaxel
Paclitaxel has a long list of both approved and off-label uses in malignancies as a primary agent and in conjunction with other drugs. The FDA prescribing information for Taxol and Abraxane was last updated in April 2011 and September 2020, respectively.20,21 The National Institutes of Health National Library of Medicine has the current update for paclitaxel on July 2023.19,22 Thus, the prescribed information for paclitaxel referenced in the database may not always be up to date. The combinations of paclitaxel with bevacizumab, carboplatin, or carboplatin and pembrolizumab were not in the Taxol prescribing information. Likewise, a combination of nab-paclitaxel with atezolizumab or carboplatin and pembrolizumab is missing in the Abraxane prescribing information.22-27
The generic name is not the same as a generic drug, which may have slight differences from the brand name product.71 The generic drug versions of Taxol and Abraxane have been approved by the FDA as paclitaxel injectable and paclitaxel-protein bound, respectively. There was a global shortage of nab-paclitaxel from October 2021 to June 2022 because of a manufacturing problem.72 During this shortage, data showed similar comments from physician documents that treatment switched to Taxol due to the Abraxane shortage.
Of 336 patients in the PDTS database with dispensed paclitaxel prescriptions, 276 received paclitaxel (year dispensed, 2013-2022), 27 received Abraxane (year dispensed, 2013-2022), 47 received Taxol (year dispensed, 2004-2015), 8 received both Abraxane and paclitaxel, and 6 received both Taxol and paclitaxel. Based on this information, it appears that the distinction between the drugs was not made in the PDTS until after 2015, 10 years after Abraxane received FDA approval. Abraxane was prescribed in the MHS in 2013, 8 years after FDA approval. There were a few comparison studies of Abraxane and Taxol.73-76
Safety and effectiveness in pediatric patients have not been established for paclitaxel. According to the DoD Cancer Registry Program, the youngest patient was aged 2 months. In 2021, this patient was diagnosed with corpus uteri and treated with carboplatin and Taxol in course 1; in course 2, the patient reacted to Taxol; in course 3, Taxol was replaced with Abraxane; in courses 4 to 7, the patient was treated with carboplatin only.
Discontinued Treatment
Ten patients had prescribed Taxol that was changed due to AEs: 1 was switched to Abraxane and atezolizumab, 3 switched to Abraxane, 2 switched to docetaxel, 1 switched to doxorubicin, and 3 switched to pembrolizumab (based on physician’s comments). Of the 10 patients, 7 had Taxol reaction, 2 experienced disease progression, and 1 experienced high programmed death–ligand 1 expression (this patient with breast cancer was switched to Abraxane and atezolizumab during the accelerated FDA approval phase for atezolizumab, which was later revoked). Five patients were treated with carboplatin and Taxol for cancer of the anal canal (changed to pembrolizumab after disease progression), lung not otherwise specified (changed to carboplatin and pembrolizumab due to Taxol reaction), lower inner quadrant of the breast (changed to doxorubicin due to hypersensitivity reaction), corpus uteri (changed to Abraxane due to Taxol reaction), and ovary (changed to docetaxel due to Taxol reaction). Three patients were treated with doxorubicin, cyclophosphamide, and Taxol for breast cancer; 2 patients with breast cancer not otherwise specified switched to Abraxane due to cardiopulmonary hypersensitivity and Taxol reaction and 1 patient with cancer of the upper outer quadrant of the breast changed to docetaxel due to allergic reaction. One patient, who was treated with paclitaxel, ifosfamide, and cisplatin for metastasis of the lower lobe of the lung and kidney cancer, experienced complications due to infectious colitis (treated with ciprofloxacin) and then switched to pembrolizumab after the disease progressed. These AEs are known in paclitaxel medical literature on paclitaxel AEs.19-24,77-81
Combining 2 or more treatments to target cancer-inducing or cell-sustaining pathways is a cornerstone of chemotherapy.82-84 Most combinations are given on the same day, but some are not. For 3- or 4-drug combinations, doxorubicin and cyclophosphamide were given first, followed by paclitaxel with or withouttrastuzumab, carboplatin, or pembrolizumab. Only 16 patients (2%) were treated with paclitaxel alone; therefore, the completed and discontinued treatment groups are mostly concomitant treatment. As a result, the comparisons of the completed and discontinued treatment groups were almost the same for the diagnosis. The PDTS data have a better result because 2 exclusion criteria were applied before narrowing the analysis down to paclitaxel treatment specifically.
Antidepressants and Other Drugs
Drug response can vary from person to person and can lead to treatment failure related to AEs. One major factor in drug metabolism is CYP.85 CYP2C8 is the major pathway for paclitaxel and CYP3A4 is the minor pathway. When evaluating the noncancer drugs, there were no reports of CYP2C8 inhibition or induction.Over the years, many DDI warnings have been issued for paclitaxel with different drugs in various electronic resources.
Oncologists follow guidelines to prevent DDIs, as paclitaxel is known to have severe, moderate, and minor interactions with other drugs. Among 687 patients, 261 (38%) were prescribed any of 14 antidepressants. Eight of these antidepressants (amitriptyline, citalopram, desipramine, doxepin, venlafaxine, escitalopram, nortriptyline, and trazodone) are metabolized, 3 (mirtazapine, sertraline, and fluoxetine) are metabolized and inhibited, 2 (bupropion and duloxetine) are neither metabolized nor inhibited, and 1 (paroxetine) is inhibited by CYP3A4. Duloxetine, venlafaxine, and trazodone were more commonly dispensed (84, 78, and 42 patients, respectively) than others (≤ 33 patients).
Of 32 patients with documented AEs,14 (44%) had 168 dispensed drugs in the PDTS database. Six patients (19%) were treated with doxorubicin and cyclophosphamide followed by paclitaxel for breast cancer; 6 (19%) were treated with carboplatin and paclitaxel for cancer of the lung (n = 3), corpus uteri (n = 2), and ovary (n = 1); 1 patient (3%) was treated with carboplatin and paclitaxel, then switched to carboplatin, bevacizumab, and paclitaxel, and then completed treatment with carboplatin and paclitaxel for an unspecified female genital cancer; and 1 patient (3%) was treated with cisplatin, ifosfamide, and paclitaxel for metastasis of the lower lobe lung and kidney cancer.
The 14 patients with PDTS data had 18 cancer drugs dispensed. Eleven had moderate interaction reports and 7 had no interaction reports. A total of 165 noncancer drugs were dispensed, of which 3 were antidepressants and had no interactions reported, 8 had moderate interactions reported, and 2 had minor interactions with Taxol and Abraxane, respectively (Table 6).86-129
Of 3 patients who were dispensed bupropion, nortriptyline, or paroxetine, 1 patient with breast cancer was treated with doxorubicin andcyclophosphamide, followed by paclitaxel with bupropion, nortriptyline, pegfilgrastim,dexamethasone, and 17 other noncancer drugs that had no interaction report dispensed during paclitaxel treatment. Of 2 patients with lung cancer, 1 patient was treated with carboplatin and paclitaxel with nortriptyline, dexamethasone, and 13 additional medications, and the second patient was treated with paroxetine, cimetidine, dexamethasone, and 12 other medications. Patients were dispensed up to6 noncancer medications on the same day as paclitaxel administration to control the AEs, not including the prodrugs filled before the treatments. Paroxetine and cimetidine have weak inhibition, and dexamethasone has weak induction of CYP3A4. Therefore, while 1:1 DDIs might have little or no effect with weak inhibit/induce CYP3A4 drugs, 1:1:1 or more combinations could have a different outcome (confirmed in previous publications).65-67
Dispensed on the same day may not mean taken at the same time. One patient experienced an AE with dispensed 50 mg losartan, carboplatin plus paclitaxel, dexamethasone, and 6 other noncancer drugs. Losartan inhibits paclitaxel, which can lead to negative AEs.57,66,67 However, there were no blood or plasma samples taken to confirm the losartan was taken at the same time as the paclitaxel given this was not a clinical trial.
Conclusions
This retrospective study discusses the use of paclitaxel in the MHS and the potential DDIs associated with it. The study population consisted mostly of active-duty personnel, who are required to be healthy or have controlled or nonactive medical diagnoses and be physically fit. This group is mixed with dependents and retirees that are more reflective of the average US population. As a result, this patient population is healthier than the general population, with a lower prevalence of common illnesses such as diabetes and obesity. The study aimed to identify drugs used alongside paclitaxel treatment. While further research is needed to identify potential DDIs among patients who experienced AEs, in vitro testing will need to be conducted before confirming causality. The low number of AEs experienced by only 32 of 702 patients (5%), with no deaths during paclitaxel treatment, indicates that the drug is generally well tolerated. Although this study cannot conclude that concomitant use with noncancer drugs led to the discontinuation of paclitaxel, we can conclude that there seems to be no significant DDIsidentified between paclitaxel and antidepressants. This comprehensive overview provides clinicians with a complete picture of paclitaxel use for 27 years (1996-2022), enabling them to make informed decisions about paclitaxel treatment.
Acknowledgments
The Department of Research Program funds at Walter Reed National Military Medical Center supported this protocol. We sincerely appreciate the contribution of data extraction from the Joint Pathology Center teams (Francisco J. Rentas, John D. McGeeney, Beatriz A. Hallo, and Johnny P. Beason) and the MHS database personnel (Maj Ryan Costantino, Brandon E. Jenkins, and Alexander G. Rittel). We gratefully thank you for the protocol support from the Department of Research programs: CDR Martin L. Boese, CDR Wesley R. Campbell, Maj. Abhimanyu Chandel, CDR Ling Ye, Chelsea N. Powers, Yaling Zhou, Elizabeth Schafer, Micah Stretch, Diane Beaner, and Adrienne Woodard.
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Background
Paclitaxel was first derived from the bark of the yew tree (Taxus brevifolia). It was discovered as part of a National Cancer Institute program screen of plants and natural products with putative anticancer activity during the 1960s.1-9 Paclitaxel works by suppressing spindle microtube dynamics, which results in the blockage of the metaphase-anaphase transitions, inhibition of mitosis, and induction of apoptosis in a broad spectrum of cancer cells. Paclitaxel also displayed additional anticancer activities, including the suppression of cell proliferation and antiangiogenic effects. However, since the growth of normal body cells may also be affected, other adverse effects (AEs) will also occur.8-18
Two different chemotherapy drugs contain paclitaxel—paclitaxel and nab-paclitaxel—and the US Food and Drug Administration (FDA) recognizes them as separate entities.19-21 Taxol (paclitaxel) was approved by the FDA in 1992 for treating advanced ovarian cancer.20 It has since been approved for the treatment of metastatic breast cancer, AIDS-related Kaposi sarcoma (as an orphan drug), non-small cell lung cancer (NSCLC), and cervical cancers (in combination withbevacizumab) in 1994, 1997, 1999, and 2014, respectively.21 Since 2002, a generic version of Taxol, known as paclitaxel injectable, has been FDA-approved from different manufacturers. According to the National Cancer Institute, a combination of carboplatin and Taxol is approved to treat carcinoma of unknown primary, cervical, endometrial, NSCLC, ovarian, and thymoma cancers.19 Abraxane (nab-paclitaxel) was FDA-approved to treat metastatic breast cancer in 2005. It was later approved for first-line treatment of advanced NSCLC and late-stage pancreatic cancer in 2012 and 2013, respectively. In 2018 and 2020, both Taxol and Abraxane were approved for first-line treatment of metastatic squamous cell NSCLC in combination with carboplatin and pembrolizumab and metastatic triple-negative breast cancer in combination with pembrolizumab, respectively.22-26 In 2019, Abraxane was approved with atezolizumab to treat metastatic triple-negative breast cancer, but this approval was withdrawn in 2021. In 2022, a generic version of Abraxane, known as paclitaxel protein-bound, was released in the United States. Furthermore, paclitaxel-containing formulations also are being studied in the treatment of other types of cancer.19-32
One of the main limitations of paclitaxel is its low solubility in water, which complicates its drug supply. To distribute this hydrophobic anticancer drug efficiently, paclitaxel is formulated and administered to patients via polyethoxylated castor oil or albumin-bound (nab-paclitaxel). However, polyethoxylated castor oil induces complement activation and is the cause of common hypersensitivity reactions related to paclitaxel use.2,17,33-38 Therefore, many alternatives to polyethoxylated castor oil have been researched.
Since 2000, new paclitaxel formulations have emerged using nanomedicine techniques. The difference between these formulations is the drug vehicle. Different paclitaxel-based nanotechnological vehicles have been developed and approved, such as albumin-based nanoparticles, polymeric lipidic nanoparticles, polymeric micelles, and liposomes, with many others in clinical trial phases.3,37 Albumin-based nanoparticles have a high response rate (33%), whereas the response rate for polyethoxylated castor oil is 25% in patients with metastatic breast cancer.33,39-52 The use of paclitaxel dimer nanoparticles also has been proposed as a method for increasing drug solubility.33,53
Paclitaxel is metabolized by cytochrome P450 (CYP) isoenzymes 2C8 and 3A4. When administering paclitaxel with known inhibitors, inducers, or substrates of CYP2C8 or CYP3A4, caution is required.19-22 Regulations for CYP research were not issued until 2008, so potential interactions between paclitaxel and other drugs have not been extensively evaluated in clinical trials. A study of 12 kinase inhibitors showed strong inhibition of CYP2C8 and/or CYP3A4 pathways by these inhibitors, which could alter the ratio of paclitaxel metabolites in vivo, leading to clinically relevant changes.54 Differential metabolism has been linked to paclitaxel-induced neurotoxicity in patients with cancer.55 Nonetheless, variants in the CYP2C8, CYP3A4, CYP3A5, and ABCB1 genes do not account for significant interindividual variability in paclitaxel pharmacokinetics.56 In liver microsomes, losartan inhibited paclitaxel metabolism when used at concentrations > 50 µmol/L.57 Many drug-drug interaction (DDI) studies of CYP2C8 and CYP3A4 have shown similar results for paclitaxel.58-64
The goals of this study are to investigate prescribed drugs used with paclitaxel and determine patient outcomes through several Military Health System (MHS) databases. The investigation focused on (1) the functions of paclitaxel; (2) identifying AEs that patients experienced; (3) evaluating differences when paclitaxel is used alone vs concomitantly and between the completed vs discontinued treatment groups; (4) identifying all drugs used during paclitaxel treatment; and (5) evaluating DDIs with antidepressants (that have an FDA boxed warning and are known to have DDIs confirmed in previous publications) and other drugs.65-67
The Walter Reed National Military Medical Center in Bethesda, Maryland, institutionalreview board approved the study protocol and ensured compliance with the Health Insurance Portability and Accountability Act as an exempt protocol. The Joint Pathology Center (JPC) of the US Department of Defense (DoD) Cancer Registry Program and MHS data experts from the Comprehensive Ambulatory/Professional Encounter Record (CAPER) and the Pharmacy Data Transaction Service (PDTS) provided data for the analysis.
METHODS
The DoD Cancer Registry Program was established in 1986 and currently contains data from 1998 to 2024. CAPER and PDTS are part of the MHS Data Repository/Management Analysis and Reporting Tool database. Each observation in the CAPER record represents an ambulatory encounter at a military treatment facility (MTF). CAPER includes data from 2003 to 2024.
Each observation in the PDTS record represents a prescription filled for an MHS beneficiary at an MTF through the TRICARE mail-order program or a US retail pharmacy. Missing from this record are prescriptions filled at international civilian pharmacies and inpatient pharmacy prescriptions. The MHS Data Repository PDTS record is available from 2002 to 2024. The legacy Composite Health Care System is being replaced by GENESIS at MTFs.
Data Extraction Design
The study design involved a cross-sectional analysis. We requested data extraction for paclitaxel from 1998 to 2022. Data from the DoD Cancer Registry Program were used to identify patients who received cancer treatment. Once patients were identified, the CAPER database was searched for diagnoses to identify other health conditions, whereas the PDTS database was used to populate a list of prescription medications filled during chemotherapy treatment.
Data collected from the JPC included cancer treatment, cancer information, demographics, and physicians’ comments on AEs. Collected data from the MHS include diagnosis and filled prescription history from initiation to completion of the therapy period (or 2 years after the diagnosis date). For the analysis of the DoD Cancer Registry Program and CAPER databases, we used all collected data without excluding any. When analyzing PDTS data, we excluded patients with PDTS data but without a record of paclitaxel being filled, or medications filled outside the chemotherapy period (by evaluating the dispensed date and day of supply).
Data Extraction Analysis
The Surveillance, Epidemiology, and End Results Program Coding and Staging Manual 2016 and the International Classification of Diseases for Oncology, 3rd edition, 1st revision, were used to decode disease and cancer types.68,69 Data sorting and analysis were performed using Microsoft Excel. The percentage for the total was calculated by using the number of patients or data available within the paclitaxel groups divided by the total number of patients or data variables. The subgroup percentage was calculated by using the number of patients or data available within the subgroup divided by the total number of patients in that subgroup.
In alone vs concomitant and completed vs discontinued treatment groups, a 2-tailed, 2-sample z test was used to statistical significance (P < .05) using a statistics website.70 Concomitant was defined as paclitaxel taken with other antineoplastic agent(s) before, after, or at the same time as cancer therapy. For the retrospective data analysis, physicians’ notes with a period, comma, forward slash, semicolon, or space between medication names were interpreted as concurrent, whereas plus (+), minus/plus (-/+), or “and” between drug names that were dispensed on the same day were interpreted as combined with known common combinations: 2 drugs (DM886 paclitaxel and carboplatin and DM881-TC-1 paclitaxel and cisplatin) or 3 drugs (DM887-ACT doxorubicin, cyclophosphamide, and paclitaxel). Completed treatment was defined as paclitaxel as the last medication the patient took without recorded AEs; switching or experiencing AEs was defined as discontinued treatment.
RESULTS
The JPC provided 702 entries for 687 patients with a mean age of 56 years (range, 2 months to 88 years) who were treated with paclitaxel from March 1996 to October 2021. Fifteen patients had duplicate entries because they had multiple cancer sites or occurrences. There were 623 patients (89%) who received paclitaxel for FDA-approved indications. The most common types of cancer identified were 344 patients with breast cancer (49%), 91 patients with lung cancer (13%), 79 patients with ovarian cancer (11%), and 75 patients with endometrial cancer (11%) (Table 1). Seventy-nine patients (11%) received paclitaxel for cancers that were not for FDA-approved indications, including 19 for cancers of the fallopian tube (3%) and 17 for esophageal cancer (2%) (Table 2).
There were 477 patients (68%) aged > 50 years. A total of 304 patients (43%) had a stage III or IV cancer diagnosis and 398 (57%) had stage II or lower (combination of data for stages 0, I, and II; not applicable; and unknown) cancer diagnosis. For systemic treatment, 16 patients (2%) were treated with paclitaxel alone and 686 patients (98%) received paclitaxel concomitantly with additional chemotherapy: 59 patients (9%) in the before or after group, 410 patients (58%) had a 2-drug combination, 212 patients (30%) had a 3-drug combination, and 5 patients (1%) had a 4-drug combination. In addition, for doublet therapies, paclitaxel combined with carboplatin, trastuzumab, gemcitabine, or cisplatin had more patients (318, 58, 12, and 11, respectively) than other combinations (≤ 4 patients). For triplet therapies, paclitaxel combined withdoxorubicin plus cyclophosphamide or carboplatin plus bevacizumab had more patients (174 and 20, respectively) than other combinations, including quadruplet therapies (≤ 4 patients) (Table 3).
Patients were more likely to discontinue paclitaxel if they received concomitant treatment. None of the 16 patients receiving paclitaxel monotherapy experienced AEs, whereas 364 of 686 patients (53%) treated concomitantly discontinued (P < .001). Comparisons of 1 drug vs combination (2 to 4 drugs) and use for treating cancers that were FDA-approved indications vs off-label use were significant (P < .001), whereas comparisons of stage II or lower vs stage III and IV cancer and of those aged ≤ 50 years vs aged > 50 years were not significant (P = .50 andP = .30, respectively) (Table 4).
Among the 364 patients who had concomitant treatment and had discontinued their treatment, 332 (91%) switched treatments with no AEs documented and 32 (9%) experienced fatigue with pneumonia, mucositis, neuropathy, neurotoxicity, neutropenia, pneumonitis, allergic or hypersensitivity reaction, or an unknown AE. Patients who discontinued treatment because of unknown AEs had a physician’s note that detailed progressive disease, a significant decline in performance status, and another unknown adverse effect due to a previous sinus tract infection and infectious colitis (Table 5).
Management Analysis and Reporting Tool Database
MHS data analysts provided data on diagnoses for 639 patients among 687 submitteddiagnoses, with 294 patients completing and 345 discontinuing paclitaxel treatment. Patients in the completed treatment group had 3 to 258 unique health conditions documented, while patients in the discontinued treatment group had 4 to 181 unique health conditions documented. The MHS reported 3808 unique diagnosis conditions for the completed group and 3714 for the discontinued group (P = .02).
The mean (SD) number of diagnoses was 51 (31) for the completed and 55 (28) for the discontinued treatment groups (Figure). Among 639 patients who received paclitaxel, the top 5 diagnoses were administrative, including encounters for other administrative examinations; antineoplastic chemotherapy; administrative examination for unspecified; other specified counseling; and adjustment and management of vascular access device. The database does not differentiate between administrative and clinically significant diagnoses.
MHS data analysts provided data for 336 of 687 submitted patients who were prescribed paclitaxel; 46 patients had no PDTS data, and 305 patients had PDTS data without paclitaxel, Taxol, or Abraxane dispensed. Medications that were filled outside the chemotherapy period were removed by evaluating the dispensed date and day of supply. Among these 336 patients, 151 completed the treatment and 185 discontinued, with 14 patients experiencing documented AEs. Patients in the completed treatment group filled 9 to 56 prescriptions while patients in the discontinued treatment group filled 6 to 70 prescriptions.Patients in the discontinued group filled more prescriptions than those who completed treatment: 793 vs 591, respectively (P = .34).
The mean (SD) number of filled prescription drugs was 24 (9) for the completed and 34 (12) for the discontinued treatment group. The 5 most filled prescriptions with paclitaxel from 336 patients with PDTS data were dexamethasone (324 prescriptions with 14 recorded AEs), diphenhydramine (296 prescriptions with 12 recorded AEs), ondansetron (277 prescriptions with 11 recorded AEs), prochlorperazine (265 prescriptions with 12 recorded AEs), and sodium chloride (232 prescriptions with 11 recorded AEs).
DISCUSSION
As a retrospective review, this study is more limited in the strength of its conclusions when compared to randomized control trials. The DoD Cancer Registry Program only contains information about cancer types, stages, treatment regimens, and physicians’ notes. Therefore, noncancer drugs are based solely on the PDTS database. In most cases, physicians' notes on AEs were not detailed. There was no distinction between initial vs later lines of therapy and dosage reductions. The change in status or appearance of a new medical condition did not indicate whether paclitaxel caused the changes to develop or directly worsen a pre-existing condition. The PDTS records prescriptions filled, but that may not reflect patients taking prescriptions.
Paclitaxel
Paclitaxel has a long list of both approved and off-label uses in malignancies as a primary agent and in conjunction with other drugs. The FDA prescribing information for Taxol and Abraxane was last updated in April 2011 and September 2020, respectively.20,21 The National Institutes of Health National Library of Medicine has the current update for paclitaxel on July 2023.19,22 Thus, the prescribed information for paclitaxel referenced in the database may not always be up to date. The combinations of paclitaxel with bevacizumab, carboplatin, or carboplatin and pembrolizumab were not in the Taxol prescribing information. Likewise, a combination of nab-paclitaxel with atezolizumab or carboplatin and pembrolizumab is missing in the Abraxane prescribing information.22-27
The generic name is not the same as a generic drug, which may have slight differences from the brand name product.71 The generic drug versions of Taxol and Abraxane have been approved by the FDA as paclitaxel injectable and paclitaxel-protein bound, respectively. There was a global shortage of nab-paclitaxel from October 2021 to June 2022 because of a manufacturing problem.72 During this shortage, data showed similar comments from physician documents that treatment switched to Taxol due to the Abraxane shortage.
Of 336 patients in the PDTS database with dispensed paclitaxel prescriptions, 276 received paclitaxel (year dispensed, 2013-2022), 27 received Abraxane (year dispensed, 2013-2022), 47 received Taxol (year dispensed, 2004-2015), 8 received both Abraxane and paclitaxel, and 6 received both Taxol and paclitaxel. Based on this information, it appears that the distinction between the drugs was not made in the PDTS until after 2015, 10 years after Abraxane received FDA approval. Abraxane was prescribed in the MHS in 2013, 8 years after FDA approval. There were a few comparison studies of Abraxane and Taxol.73-76
Safety and effectiveness in pediatric patients have not been established for paclitaxel. According to the DoD Cancer Registry Program, the youngest patient was aged 2 months. In 2021, this patient was diagnosed with corpus uteri and treated with carboplatin and Taxol in course 1; in course 2, the patient reacted to Taxol; in course 3, Taxol was replaced with Abraxane; in courses 4 to 7, the patient was treated with carboplatin only.
Discontinued Treatment
Ten patients had prescribed Taxol that was changed due to AEs: 1 was switched to Abraxane and atezolizumab, 3 switched to Abraxane, 2 switched to docetaxel, 1 switched to doxorubicin, and 3 switched to pembrolizumab (based on physician’s comments). Of the 10 patients, 7 had Taxol reaction, 2 experienced disease progression, and 1 experienced high programmed death–ligand 1 expression (this patient with breast cancer was switched to Abraxane and atezolizumab during the accelerated FDA approval phase for atezolizumab, which was later revoked). Five patients were treated with carboplatin and Taxol for cancer of the anal canal (changed to pembrolizumab after disease progression), lung not otherwise specified (changed to carboplatin and pembrolizumab due to Taxol reaction), lower inner quadrant of the breast (changed to doxorubicin due to hypersensitivity reaction), corpus uteri (changed to Abraxane due to Taxol reaction), and ovary (changed to docetaxel due to Taxol reaction). Three patients were treated with doxorubicin, cyclophosphamide, and Taxol for breast cancer; 2 patients with breast cancer not otherwise specified switched to Abraxane due to cardiopulmonary hypersensitivity and Taxol reaction and 1 patient with cancer of the upper outer quadrant of the breast changed to docetaxel due to allergic reaction. One patient, who was treated with paclitaxel, ifosfamide, and cisplatin for metastasis of the lower lobe of the lung and kidney cancer, experienced complications due to infectious colitis (treated with ciprofloxacin) and then switched to pembrolizumab after the disease progressed. These AEs are known in paclitaxel medical literature on paclitaxel AEs.19-24,77-81
Combining 2 or more treatments to target cancer-inducing or cell-sustaining pathways is a cornerstone of chemotherapy.82-84 Most combinations are given on the same day, but some are not. For 3- or 4-drug combinations, doxorubicin and cyclophosphamide were given first, followed by paclitaxel with or withouttrastuzumab, carboplatin, or pembrolizumab. Only 16 patients (2%) were treated with paclitaxel alone; therefore, the completed and discontinued treatment groups are mostly concomitant treatment. As a result, the comparisons of the completed and discontinued treatment groups were almost the same for the diagnosis. The PDTS data have a better result because 2 exclusion criteria were applied before narrowing the analysis down to paclitaxel treatment specifically.
Antidepressants and Other Drugs
Drug response can vary from person to person and can lead to treatment failure related to AEs. One major factor in drug metabolism is CYP.85 CYP2C8 is the major pathway for paclitaxel and CYP3A4 is the minor pathway. When evaluating the noncancer drugs, there were no reports of CYP2C8 inhibition or induction.Over the years, many DDI warnings have been issued for paclitaxel with different drugs in various electronic resources.
Oncologists follow guidelines to prevent DDIs, as paclitaxel is known to have severe, moderate, and minor interactions with other drugs. Among 687 patients, 261 (38%) were prescribed any of 14 antidepressants. Eight of these antidepressants (amitriptyline, citalopram, desipramine, doxepin, venlafaxine, escitalopram, nortriptyline, and trazodone) are metabolized, 3 (mirtazapine, sertraline, and fluoxetine) are metabolized and inhibited, 2 (bupropion and duloxetine) are neither metabolized nor inhibited, and 1 (paroxetine) is inhibited by CYP3A4. Duloxetine, venlafaxine, and trazodone were more commonly dispensed (84, 78, and 42 patients, respectively) than others (≤ 33 patients).
Of 32 patients with documented AEs,14 (44%) had 168 dispensed drugs in the PDTS database. Six patients (19%) were treated with doxorubicin and cyclophosphamide followed by paclitaxel for breast cancer; 6 (19%) were treated with carboplatin and paclitaxel for cancer of the lung (n = 3), corpus uteri (n = 2), and ovary (n = 1); 1 patient (3%) was treated with carboplatin and paclitaxel, then switched to carboplatin, bevacizumab, and paclitaxel, and then completed treatment with carboplatin and paclitaxel for an unspecified female genital cancer; and 1 patient (3%) was treated with cisplatin, ifosfamide, and paclitaxel for metastasis of the lower lobe lung and kidney cancer.
The 14 patients with PDTS data had 18 cancer drugs dispensed. Eleven had moderate interaction reports and 7 had no interaction reports. A total of 165 noncancer drugs were dispensed, of which 3 were antidepressants and had no interactions reported, 8 had moderate interactions reported, and 2 had minor interactions with Taxol and Abraxane, respectively (Table 6).86-129
Of 3 patients who were dispensed bupropion, nortriptyline, or paroxetine, 1 patient with breast cancer was treated with doxorubicin andcyclophosphamide, followed by paclitaxel with bupropion, nortriptyline, pegfilgrastim,dexamethasone, and 17 other noncancer drugs that had no interaction report dispensed during paclitaxel treatment. Of 2 patients with lung cancer, 1 patient was treated with carboplatin and paclitaxel with nortriptyline, dexamethasone, and 13 additional medications, and the second patient was treated with paroxetine, cimetidine, dexamethasone, and 12 other medications. Patients were dispensed up to6 noncancer medications on the same day as paclitaxel administration to control the AEs, not including the prodrugs filled before the treatments. Paroxetine and cimetidine have weak inhibition, and dexamethasone has weak induction of CYP3A4. Therefore, while 1:1 DDIs might have little or no effect with weak inhibit/induce CYP3A4 drugs, 1:1:1 or more combinations could have a different outcome (confirmed in previous publications).65-67
Dispensed on the same day may not mean taken at the same time. One patient experienced an AE with dispensed 50 mg losartan, carboplatin plus paclitaxel, dexamethasone, and 6 other noncancer drugs. Losartan inhibits paclitaxel, which can lead to negative AEs.57,66,67 However, there were no blood or plasma samples taken to confirm the losartan was taken at the same time as the paclitaxel given this was not a clinical trial.
Conclusions
This retrospective study discusses the use of paclitaxel in the MHS and the potential DDIs associated with it. The study population consisted mostly of active-duty personnel, who are required to be healthy or have controlled or nonactive medical diagnoses and be physically fit. This group is mixed with dependents and retirees that are more reflective of the average US population. As a result, this patient population is healthier than the general population, with a lower prevalence of common illnesses such as diabetes and obesity. The study aimed to identify drugs used alongside paclitaxel treatment. While further research is needed to identify potential DDIs among patients who experienced AEs, in vitro testing will need to be conducted before confirming causality. The low number of AEs experienced by only 32 of 702 patients (5%), with no deaths during paclitaxel treatment, indicates that the drug is generally well tolerated. Although this study cannot conclude that concomitant use with noncancer drugs led to the discontinuation of paclitaxel, we can conclude that there seems to be no significant DDIsidentified between paclitaxel and antidepressants. This comprehensive overview provides clinicians with a complete picture of paclitaxel use for 27 years (1996-2022), enabling them to make informed decisions about paclitaxel treatment.
Acknowledgments
The Department of Research Program funds at Walter Reed National Military Medical Center supported this protocol. We sincerely appreciate the contribution of data extraction from the Joint Pathology Center teams (Francisco J. Rentas, John D. McGeeney, Beatriz A. Hallo, and Johnny P. Beason) and the MHS database personnel (Maj Ryan Costantino, Brandon E. Jenkins, and Alexander G. Rittel). We gratefully thank you for the protocol support from the Department of Research programs: CDR Martin L. Boese, CDR Wesley R. Campbell, Maj. Abhimanyu Chandel, CDR Ling Ye, Chelsea N. Powers, Yaling Zhou, Elizabeth Schafer, Micah Stretch, Diane Beaner, and Adrienne Woodard.
Background
Paclitaxel was first derived from the bark of the yew tree (Taxus brevifolia). It was discovered as part of a National Cancer Institute program screen of plants and natural products with putative anticancer activity during the 1960s.1-9 Paclitaxel works by suppressing spindle microtube dynamics, which results in the blockage of the metaphase-anaphase transitions, inhibition of mitosis, and induction of apoptosis in a broad spectrum of cancer cells. Paclitaxel also displayed additional anticancer activities, including the suppression of cell proliferation and antiangiogenic effects. However, since the growth of normal body cells may also be affected, other adverse effects (AEs) will also occur.8-18
Two different chemotherapy drugs contain paclitaxel—paclitaxel and nab-paclitaxel—and the US Food and Drug Administration (FDA) recognizes them as separate entities.19-21 Taxol (paclitaxel) was approved by the FDA in 1992 for treating advanced ovarian cancer.20 It has since been approved for the treatment of metastatic breast cancer, AIDS-related Kaposi sarcoma (as an orphan drug), non-small cell lung cancer (NSCLC), and cervical cancers (in combination withbevacizumab) in 1994, 1997, 1999, and 2014, respectively.21 Since 2002, a generic version of Taxol, known as paclitaxel injectable, has been FDA-approved from different manufacturers. According to the National Cancer Institute, a combination of carboplatin and Taxol is approved to treat carcinoma of unknown primary, cervical, endometrial, NSCLC, ovarian, and thymoma cancers.19 Abraxane (nab-paclitaxel) was FDA-approved to treat metastatic breast cancer in 2005. It was later approved for first-line treatment of advanced NSCLC and late-stage pancreatic cancer in 2012 and 2013, respectively. In 2018 and 2020, both Taxol and Abraxane were approved for first-line treatment of metastatic squamous cell NSCLC in combination with carboplatin and pembrolizumab and metastatic triple-negative breast cancer in combination with pembrolizumab, respectively.22-26 In 2019, Abraxane was approved with atezolizumab to treat metastatic triple-negative breast cancer, but this approval was withdrawn in 2021. In 2022, a generic version of Abraxane, known as paclitaxel protein-bound, was released in the United States. Furthermore, paclitaxel-containing formulations also are being studied in the treatment of other types of cancer.19-32
One of the main limitations of paclitaxel is its low solubility in water, which complicates its drug supply. To distribute this hydrophobic anticancer drug efficiently, paclitaxel is formulated and administered to patients via polyethoxylated castor oil or albumin-bound (nab-paclitaxel). However, polyethoxylated castor oil induces complement activation and is the cause of common hypersensitivity reactions related to paclitaxel use.2,17,33-38 Therefore, many alternatives to polyethoxylated castor oil have been researched.
Since 2000, new paclitaxel formulations have emerged using nanomedicine techniques. The difference between these formulations is the drug vehicle. Different paclitaxel-based nanotechnological vehicles have been developed and approved, such as albumin-based nanoparticles, polymeric lipidic nanoparticles, polymeric micelles, and liposomes, with many others in clinical trial phases.3,37 Albumin-based nanoparticles have a high response rate (33%), whereas the response rate for polyethoxylated castor oil is 25% in patients with metastatic breast cancer.33,39-52 The use of paclitaxel dimer nanoparticles also has been proposed as a method for increasing drug solubility.33,53
Paclitaxel is metabolized by cytochrome P450 (CYP) isoenzymes 2C8 and 3A4. When administering paclitaxel with known inhibitors, inducers, or substrates of CYP2C8 or CYP3A4, caution is required.19-22 Regulations for CYP research were not issued until 2008, so potential interactions between paclitaxel and other drugs have not been extensively evaluated in clinical trials. A study of 12 kinase inhibitors showed strong inhibition of CYP2C8 and/or CYP3A4 pathways by these inhibitors, which could alter the ratio of paclitaxel metabolites in vivo, leading to clinically relevant changes.54 Differential metabolism has been linked to paclitaxel-induced neurotoxicity in patients with cancer.55 Nonetheless, variants in the CYP2C8, CYP3A4, CYP3A5, and ABCB1 genes do not account for significant interindividual variability in paclitaxel pharmacokinetics.56 In liver microsomes, losartan inhibited paclitaxel metabolism when used at concentrations > 50 µmol/L.57 Many drug-drug interaction (DDI) studies of CYP2C8 and CYP3A4 have shown similar results for paclitaxel.58-64
The goals of this study are to investigate prescribed drugs used with paclitaxel and determine patient outcomes through several Military Health System (MHS) databases. The investigation focused on (1) the functions of paclitaxel; (2) identifying AEs that patients experienced; (3) evaluating differences when paclitaxel is used alone vs concomitantly and between the completed vs discontinued treatment groups; (4) identifying all drugs used during paclitaxel treatment; and (5) evaluating DDIs with antidepressants (that have an FDA boxed warning and are known to have DDIs confirmed in previous publications) and other drugs.65-67
The Walter Reed National Military Medical Center in Bethesda, Maryland, institutionalreview board approved the study protocol and ensured compliance with the Health Insurance Portability and Accountability Act as an exempt protocol. The Joint Pathology Center (JPC) of the US Department of Defense (DoD) Cancer Registry Program and MHS data experts from the Comprehensive Ambulatory/Professional Encounter Record (CAPER) and the Pharmacy Data Transaction Service (PDTS) provided data for the analysis.
METHODS
The DoD Cancer Registry Program was established in 1986 and currently contains data from 1998 to 2024. CAPER and PDTS are part of the MHS Data Repository/Management Analysis and Reporting Tool database. Each observation in the CAPER record represents an ambulatory encounter at a military treatment facility (MTF). CAPER includes data from 2003 to 2024.
Each observation in the PDTS record represents a prescription filled for an MHS beneficiary at an MTF through the TRICARE mail-order program or a US retail pharmacy. Missing from this record are prescriptions filled at international civilian pharmacies and inpatient pharmacy prescriptions. The MHS Data Repository PDTS record is available from 2002 to 2024. The legacy Composite Health Care System is being replaced by GENESIS at MTFs.
Data Extraction Design
The study design involved a cross-sectional analysis. We requested data extraction for paclitaxel from 1998 to 2022. Data from the DoD Cancer Registry Program were used to identify patients who received cancer treatment. Once patients were identified, the CAPER database was searched for diagnoses to identify other health conditions, whereas the PDTS database was used to populate a list of prescription medications filled during chemotherapy treatment.
Data collected from the JPC included cancer treatment, cancer information, demographics, and physicians’ comments on AEs. Collected data from the MHS include diagnosis and filled prescription history from initiation to completion of the therapy period (or 2 years after the diagnosis date). For the analysis of the DoD Cancer Registry Program and CAPER databases, we used all collected data without excluding any. When analyzing PDTS data, we excluded patients with PDTS data but without a record of paclitaxel being filled, or medications filled outside the chemotherapy period (by evaluating the dispensed date and day of supply).
Data Extraction Analysis
The Surveillance, Epidemiology, and End Results Program Coding and Staging Manual 2016 and the International Classification of Diseases for Oncology, 3rd edition, 1st revision, were used to decode disease and cancer types.68,69 Data sorting and analysis were performed using Microsoft Excel. The percentage for the total was calculated by using the number of patients or data available within the paclitaxel groups divided by the total number of patients or data variables. The subgroup percentage was calculated by using the number of patients or data available within the subgroup divided by the total number of patients in that subgroup.
In alone vs concomitant and completed vs discontinued treatment groups, a 2-tailed, 2-sample z test was used to statistical significance (P < .05) using a statistics website.70 Concomitant was defined as paclitaxel taken with other antineoplastic agent(s) before, after, or at the same time as cancer therapy. For the retrospective data analysis, physicians’ notes with a period, comma, forward slash, semicolon, or space between medication names were interpreted as concurrent, whereas plus (+), minus/plus (-/+), or “and” between drug names that were dispensed on the same day were interpreted as combined with known common combinations: 2 drugs (DM886 paclitaxel and carboplatin and DM881-TC-1 paclitaxel and cisplatin) or 3 drugs (DM887-ACT doxorubicin, cyclophosphamide, and paclitaxel). Completed treatment was defined as paclitaxel as the last medication the patient took without recorded AEs; switching or experiencing AEs was defined as discontinued treatment.
RESULTS
The JPC provided 702 entries for 687 patients with a mean age of 56 years (range, 2 months to 88 years) who were treated with paclitaxel from March 1996 to October 2021. Fifteen patients had duplicate entries because they had multiple cancer sites or occurrences. There were 623 patients (89%) who received paclitaxel for FDA-approved indications. The most common types of cancer identified were 344 patients with breast cancer (49%), 91 patients with lung cancer (13%), 79 patients with ovarian cancer (11%), and 75 patients with endometrial cancer (11%) (Table 1). Seventy-nine patients (11%) received paclitaxel for cancers that were not for FDA-approved indications, including 19 for cancers of the fallopian tube (3%) and 17 for esophageal cancer (2%) (Table 2).
There were 477 patients (68%) aged > 50 years. A total of 304 patients (43%) had a stage III or IV cancer diagnosis and 398 (57%) had stage II or lower (combination of data for stages 0, I, and II; not applicable; and unknown) cancer diagnosis. For systemic treatment, 16 patients (2%) were treated with paclitaxel alone and 686 patients (98%) received paclitaxel concomitantly with additional chemotherapy: 59 patients (9%) in the before or after group, 410 patients (58%) had a 2-drug combination, 212 patients (30%) had a 3-drug combination, and 5 patients (1%) had a 4-drug combination. In addition, for doublet therapies, paclitaxel combined with carboplatin, trastuzumab, gemcitabine, or cisplatin had more patients (318, 58, 12, and 11, respectively) than other combinations (≤ 4 patients). For triplet therapies, paclitaxel combined withdoxorubicin plus cyclophosphamide or carboplatin plus bevacizumab had more patients (174 and 20, respectively) than other combinations, including quadruplet therapies (≤ 4 patients) (Table 3).
Patients were more likely to discontinue paclitaxel if they received concomitant treatment. None of the 16 patients receiving paclitaxel monotherapy experienced AEs, whereas 364 of 686 patients (53%) treated concomitantly discontinued (P < .001). Comparisons of 1 drug vs combination (2 to 4 drugs) and use for treating cancers that were FDA-approved indications vs off-label use were significant (P < .001), whereas comparisons of stage II or lower vs stage III and IV cancer and of those aged ≤ 50 years vs aged > 50 years were not significant (P = .50 andP = .30, respectively) (Table 4).
Among the 364 patients who had concomitant treatment and had discontinued their treatment, 332 (91%) switched treatments with no AEs documented and 32 (9%) experienced fatigue with pneumonia, mucositis, neuropathy, neurotoxicity, neutropenia, pneumonitis, allergic or hypersensitivity reaction, or an unknown AE. Patients who discontinued treatment because of unknown AEs had a physician’s note that detailed progressive disease, a significant decline in performance status, and another unknown adverse effect due to a previous sinus tract infection and infectious colitis (Table 5).
Management Analysis and Reporting Tool Database
MHS data analysts provided data on diagnoses for 639 patients among 687 submitteddiagnoses, with 294 patients completing and 345 discontinuing paclitaxel treatment. Patients in the completed treatment group had 3 to 258 unique health conditions documented, while patients in the discontinued treatment group had 4 to 181 unique health conditions documented. The MHS reported 3808 unique diagnosis conditions for the completed group and 3714 for the discontinued group (P = .02).
The mean (SD) number of diagnoses was 51 (31) for the completed and 55 (28) for the discontinued treatment groups (Figure). Among 639 patients who received paclitaxel, the top 5 diagnoses were administrative, including encounters for other administrative examinations; antineoplastic chemotherapy; administrative examination for unspecified; other specified counseling; and adjustment and management of vascular access device. The database does not differentiate between administrative and clinically significant diagnoses.
MHS data analysts provided data for 336 of 687 submitted patients who were prescribed paclitaxel; 46 patients had no PDTS data, and 305 patients had PDTS data without paclitaxel, Taxol, or Abraxane dispensed. Medications that were filled outside the chemotherapy period were removed by evaluating the dispensed date and day of supply. Among these 336 patients, 151 completed the treatment and 185 discontinued, with 14 patients experiencing documented AEs. Patients in the completed treatment group filled 9 to 56 prescriptions while patients in the discontinued treatment group filled 6 to 70 prescriptions.Patients in the discontinued group filled more prescriptions than those who completed treatment: 793 vs 591, respectively (P = .34).
The mean (SD) number of filled prescription drugs was 24 (9) for the completed and 34 (12) for the discontinued treatment group. The 5 most filled prescriptions with paclitaxel from 336 patients with PDTS data were dexamethasone (324 prescriptions with 14 recorded AEs), diphenhydramine (296 prescriptions with 12 recorded AEs), ondansetron (277 prescriptions with 11 recorded AEs), prochlorperazine (265 prescriptions with 12 recorded AEs), and sodium chloride (232 prescriptions with 11 recorded AEs).
DISCUSSION
As a retrospective review, this study is more limited in the strength of its conclusions when compared to randomized control trials. The DoD Cancer Registry Program only contains information about cancer types, stages, treatment regimens, and physicians’ notes. Therefore, noncancer drugs are based solely on the PDTS database. In most cases, physicians' notes on AEs were not detailed. There was no distinction between initial vs later lines of therapy and dosage reductions. The change in status or appearance of a new medical condition did not indicate whether paclitaxel caused the changes to develop or directly worsen a pre-existing condition. The PDTS records prescriptions filled, but that may not reflect patients taking prescriptions.
Paclitaxel
Paclitaxel has a long list of both approved and off-label uses in malignancies as a primary agent and in conjunction with other drugs. The FDA prescribing information for Taxol and Abraxane was last updated in April 2011 and September 2020, respectively.20,21 The National Institutes of Health National Library of Medicine has the current update for paclitaxel on July 2023.19,22 Thus, the prescribed information for paclitaxel referenced in the database may not always be up to date. The combinations of paclitaxel with bevacizumab, carboplatin, or carboplatin and pembrolizumab were not in the Taxol prescribing information. Likewise, a combination of nab-paclitaxel with atezolizumab or carboplatin and pembrolizumab is missing in the Abraxane prescribing information.22-27
The generic name is not the same as a generic drug, which may have slight differences from the brand name product.71 The generic drug versions of Taxol and Abraxane have been approved by the FDA as paclitaxel injectable and paclitaxel-protein bound, respectively. There was a global shortage of nab-paclitaxel from October 2021 to June 2022 because of a manufacturing problem.72 During this shortage, data showed similar comments from physician documents that treatment switched to Taxol due to the Abraxane shortage.
Of 336 patients in the PDTS database with dispensed paclitaxel prescriptions, 276 received paclitaxel (year dispensed, 2013-2022), 27 received Abraxane (year dispensed, 2013-2022), 47 received Taxol (year dispensed, 2004-2015), 8 received both Abraxane and paclitaxel, and 6 received both Taxol and paclitaxel. Based on this information, it appears that the distinction between the drugs was not made in the PDTS until after 2015, 10 years after Abraxane received FDA approval. Abraxane was prescribed in the MHS in 2013, 8 years after FDA approval. There were a few comparison studies of Abraxane and Taxol.73-76
Safety and effectiveness in pediatric patients have not been established for paclitaxel. According to the DoD Cancer Registry Program, the youngest patient was aged 2 months. In 2021, this patient was diagnosed with corpus uteri and treated with carboplatin and Taxol in course 1; in course 2, the patient reacted to Taxol; in course 3, Taxol was replaced with Abraxane; in courses 4 to 7, the patient was treated with carboplatin only.
Discontinued Treatment
Ten patients had prescribed Taxol that was changed due to AEs: 1 was switched to Abraxane and atezolizumab, 3 switched to Abraxane, 2 switched to docetaxel, 1 switched to doxorubicin, and 3 switched to pembrolizumab (based on physician’s comments). Of the 10 patients, 7 had Taxol reaction, 2 experienced disease progression, and 1 experienced high programmed death–ligand 1 expression (this patient with breast cancer was switched to Abraxane and atezolizumab during the accelerated FDA approval phase for atezolizumab, which was later revoked). Five patients were treated with carboplatin and Taxol for cancer of the anal canal (changed to pembrolizumab after disease progression), lung not otherwise specified (changed to carboplatin and pembrolizumab due to Taxol reaction), lower inner quadrant of the breast (changed to doxorubicin due to hypersensitivity reaction), corpus uteri (changed to Abraxane due to Taxol reaction), and ovary (changed to docetaxel due to Taxol reaction). Three patients were treated with doxorubicin, cyclophosphamide, and Taxol for breast cancer; 2 patients with breast cancer not otherwise specified switched to Abraxane due to cardiopulmonary hypersensitivity and Taxol reaction and 1 patient with cancer of the upper outer quadrant of the breast changed to docetaxel due to allergic reaction. One patient, who was treated with paclitaxel, ifosfamide, and cisplatin for metastasis of the lower lobe of the lung and kidney cancer, experienced complications due to infectious colitis (treated with ciprofloxacin) and then switched to pembrolizumab after the disease progressed. These AEs are known in paclitaxel medical literature on paclitaxel AEs.19-24,77-81
Combining 2 or more treatments to target cancer-inducing or cell-sustaining pathways is a cornerstone of chemotherapy.82-84 Most combinations are given on the same day, but some are not. For 3- or 4-drug combinations, doxorubicin and cyclophosphamide were given first, followed by paclitaxel with or withouttrastuzumab, carboplatin, or pembrolizumab. Only 16 patients (2%) were treated with paclitaxel alone; therefore, the completed and discontinued treatment groups are mostly concomitant treatment. As a result, the comparisons of the completed and discontinued treatment groups were almost the same for the diagnosis. The PDTS data have a better result because 2 exclusion criteria were applied before narrowing the analysis down to paclitaxel treatment specifically.
Antidepressants and Other Drugs
Drug response can vary from person to person and can lead to treatment failure related to AEs. One major factor in drug metabolism is CYP.85 CYP2C8 is the major pathway for paclitaxel and CYP3A4 is the minor pathway. When evaluating the noncancer drugs, there were no reports of CYP2C8 inhibition or induction.Over the years, many DDI warnings have been issued for paclitaxel with different drugs in various electronic resources.
Oncologists follow guidelines to prevent DDIs, as paclitaxel is known to have severe, moderate, and minor interactions with other drugs. Among 687 patients, 261 (38%) were prescribed any of 14 antidepressants. Eight of these antidepressants (amitriptyline, citalopram, desipramine, doxepin, venlafaxine, escitalopram, nortriptyline, and trazodone) are metabolized, 3 (mirtazapine, sertraline, and fluoxetine) are metabolized and inhibited, 2 (bupropion and duloxetine) are neither metabolized nor inhibited, and 1 (paroxetine) is inhibited by CYP3A4. Duloxetine, venlafaxine, and trazodone were more commonly dispensed (84, 78, and 42 patients, respectively) than others (≤ 33 patients).
Of 32 patients with documented AEs,14 (44%) had 168 dispensed drugs in the PDTS database. Six patients (19%) were treated with doxorubicin and cyclophosphamide followed by paclitaxel for breast cancer; 6 (19%) were treated with carboplatin and paclitaxel for cancer of the lung (n = 3), corpus uteri (n = 2), and ovary (n = 1); 1 patient (3%) was treated with carboplatin and paclitaxel, then switched to carboplatin, bevacizumab, and paclitaxel, and then completed treatment with carboplatin and paclitaxel for an unspecified female genital cancer; and 1 patient (3%) was treated with cisplatin, ifosfamide, and paclitaxel for metastasis of the lower lobe lung and kidney cancer.
The 14 patients with PDTS data had 18 cancer drugs dispensed. Eleven had moderate interaction reports and 7 had no interaction reports. A total of 165 noncancer drugs were dispensed, of which 3 were antidepressants and had no interactions reported, 8 had moderate interactions reported, and 2 had minor interactions with Taxol and Abraxane, respectively (Table 6).86-129
Of 3 patients who were dispensed bupropion, nortriptyline, or paroxetine, 1 patient with breast cancer was treated with doxorubicin andcyclophosphamide, followed by paclitaxel with bupropion, nortriptyline, pegfilgrastim,dexamethasone, and 17 other noncancer drugs that had no interaction report dispensed during paclitaxel treatment. Of 2 patients with lung cancer, 1 patient was treated with carboplatin and paclitaxel with nortriptyline, dexamethasone, and 13 additional medications, and the second patient was treated with paroxetine, cimetidine, dexamethasone, and 12 other medications. Patients were dispensed up to6 noncancer medications on the same day as paclitaxel administration to control the AEs, not including the prodrugs filled before the treatments. Paroxetine and cimetidine have weak inhibition, and dexamethasone has weak induction of CYP3A4. Therefore, while 1:1 DDIs might have little or no effect with weak inhibit/induce CYP3A4 drugs, 1:1:1 or more combinations could have a different outcome (confirmed in previous publications).65-67
Dispensed on the same day may not mean taken at the same time. One patient experienced an AE with dispensed 50 mg losartan, carboplatin plus paclitaxel, dexamethasone, and 6 other noncancer drugs. Losartan inhibits paclitaxel, which can lead to negative AEs.57,66,67 However, there were no blood or plasma samples taken to confirm the losartan was taken at the same time as the paclitaxel given this was not a clinical trial.
Conclusions
This retrospective study discusses the use of paclitaxel in the MHS and the potential DDIs associated with it. The study population consisted mostly of active-duty personnel, who are required to be healthy or have controlled or nonactive medical diagnoses and be physically fit. This group is mixed with dependents and retirees that are more reflective of the average US population. As a result, this patient population is healthier than the general population, with a lower prevalence of common illnesses such as diabetes and obesity. The study aimed to identify drugs used alongside paclitaxel treatment. While further research is needed to identify potential DDIs among patients who experienced AEs, in vitro testing will need to be conducted before confirming causality. The low number of AEs experienced by only 32 of 702 patients (5%), with no deaths during paclitaxel treatment, indicates that the drug is generally well tolerated. Although this study cannot conclude that concomitant use with noncancer drugs led to the discontinuation of paclitaxel, we can conclude that there seems to be no significant DDIsidentified between paclitaxel and antidepressants. This comprehensive overview provides clinicians with a complete picture of paclitaxel use for 27 years (1996-2022), enabling them to make informed decisions about paclitaxel treatment.
Acknowledgments
The Department of Research Program funds at Walter Reed National Military Medical Center supported this protocol. We sincerely appreciate the contribution of data extraction from the Joint Pathology Center teams (Francisco J. Rentas, John D. McGeeney, Beatriz A. Hallo, and Johnny P. Beason) and the MHS database personnel (Maj Ryan Costantino, Brandon E. Jenkins, and Alexander G. Rittel). We gratefully thank you for the protocol support from the Department of Research programs: CDR Martin L. Boese, CDR Wesley R. Campbell, Maj. Abhimanyu Chandel, CDR Ling Ye, Chelsea N. Powers, Yaling Zhou, Elizabeth Schafer, Micah Stretch, Diane Beaner, and Adrienne Woodard.
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Retrospective Evaluation of Drug-Drug Interactions With Erlotinib and Gefitinib Use in the Military Health System
Most cancer treatment regimens include the administration of several chemotherapeutic agents. Drug-drug interactions (DDIs) can increase the risk of fatal adverse events and reduce therapeutic efficacy.1,2 Erlotinib, gefitinib, afatinib, osimertinib, and icotinib are epidermal growth factor receptor–tyrosine kinase inhibitors (EGFR-TKIs) that have proven efficacy for treating advanced non–small cell lung cancer (NSCLC). Erlotinib strongly inhibits cytochrome P450 (CYP) isoenzymes CYP 1A1, moderately inhibits CYP 3A4 and 2C8, and induces CYP 1A1 and 1A2.2 Gefitinib weakly inhibits CYP 2C19 and 2D6.2 CYP 3A4 inducers and inhibitors affect metabolism of both erlotinib and gefitinib.3,4
Erlotinib and gefitinib are first-generation EGFR-TKIs and have been approved for NSCLC treatment by the US Food and Drug Administration (FDA). These agents have been used since the early 2000s and increase the possibility of long-term response and survival.2,5,6 EGFR-TKIs have a range of potential DDIs, including interactions with CYP-dependent metabolism, uridine diphosphate-glucuronosyltransferase, and transporter proteins.2 Few retrospective studies have focused on the therapeutic efficacy of erlotinib, gefitinib,or the combination of these agents.7-14
DDIs from cancer and noncancer therapies could lead to treatment discontinuation and affect patient outcomes. The goals for this study were to perform a broad-scale retrospective analysis focused on investigating prescribed drugs used with erlotinib and gefitinib and determine patient outcomes as obtained through several Military Health System (MHS) databases. Our investigation focused on (1) the functions of these drugs; (2) identifying adverse effects (AEs) that patients experienced; (3) evaluating differences when these drugs are used alone vs concomitantly, and between the completed vs discontinued treatment groups; (4) identifying all drugs used during erlotinib or gefitinib treatment; and (5) evaluating DDIs with antidepressants.
This retrospective study was performed at the Department of Research Programs at Walter Reed National Military Medical Center (WRNMMC) in Bethesda, Maryland. The WRNMMC Institutional Review Board approved the study protocol and ensured compliance with the Health Insurance Portability and Accountability Act as an exempt protocol. The Joint Pathology Center of the US Department of Defense (DoD) Cancer Registry and MHS data experts from the Comprehensive Ambulatory/Professional Encounter Record (CAPER) and the Pharmacy Data Transaction Service (PDTS) provided data for the analysis.
Methods
The DoD Cancer Registry Program was established in 1986 by the Assistant Secretary of Defense for Health Affairs. The registry currently contains data from 1998 to 2023. CAPER and PDTS are part of the MHS Data Repository/Management Analysis and Reporting Tool database. Each observation in the CAPER record represents an ambulatory encounter at a military treatment facility (MTF). CAPER records are available from 2003 to 2023.
Each observation in the PDTS record represents an outpatient prescription filled for an MHS beneficiary at MTFs through the TRICARE mail-order program or a retail pharmacy in the United States. Missing from this record are prescriptions filled at civilian pharmacies outside the United States and inpatient pharmacy prescriptions. The MHS Data Repository PDTS record is available from 2002 to 2023. The Composite Health Care System—the legacy system—is being replaced by GENESIS at MTFs.
Data Extraction Design
The study design involved a cross-sectional analysis. We requested data extraction for erlotinib and gefitinib from 1998 to 2021. Data from the DoD Cancer Registry were used to identify patients who received cancer treatment. Once patients were identified, the CAPER database was searched for diagnoses to identify other health conditions, while the PDTS database was used to populate a list of prescription medications filled during chemotherapy treatment.
Data collected from the Joint Pathology Center included cancer treatment (alone or concomitant), cancer information (cancer types and stages), demographics (sex, age at diagnosis), and physicians’ comments on AEs. Collected data from the MHS include diagnosis and filled prescription history from initiation to completion of the therapy period (or a buffer of 6 months after the initial period). We used all collected data in this analysis. The only exclusion criterion was a provided physician’s note commenting that the patient did not use erlotinib or gefitinib.
Data Extraction Analysis
The Surveillance, Epidemiology, and End Results Program Coding and Staging Manual 2016 and the International Classification of Diseases for Oncology (ICD-O) were used to decode disease and cancer types.15,16 Data sorting and analysis were performed using Microsoft Excel. The percentage for the total was calculated by using the total number of patients or data available within the gefitinib and erlotinib groups divided by total number of patients or data variables. The subgroup percentage was calculated by using the number of patients or data available within the subgroup divided by the total number of patients in that subgroup.
In alone vs concomitant and completed vs discontinued treatment groups, a 2-tailed, 2-sample z test was used to calculate P to determine statistical significance (P < .05) using a statistics website.17 Concomitant was defined as erlotinib or gefitinib taken with other medication(s) before, after, or at the same time as cancer therapy. For the retrospective data analysis, physicians’ notes with “.”, “,”, “/”, “;”, (period, comma, forward slash, semicolon) or space between medication names were interpreted as concurrent, while “+”, “-/+” (plus, minus/plus), or and between drug names were interpreted as combined. Completed treatment was defined as erlotinib or gefitinib as the last medication the patient took without recorded AEs; switching or experiencing AEs was defined as discontinued treatment.
Results
Erlotinib
The Joint Pathology Center provided 387 entries for 382 patients aged 21 to 93 years (mean, 65 years) who were treated systemically with erlotinib from January 1, 2001, to December 31, 2020. Five patients had duplicate entries because they had different cancer sites. There were 287 patients (74%) with lung cancer, 61 (16%) with pancreatic cancer, and 39 (10%) with other cancers. For lung cancer, there were 118 patients (30%) for the upper lobe, 78 (20%) for the lower lobe, and 60 (16%) not otherwise specified (NOS). Other lung cancer sites had fewer patients: 21 (5%) middle lobe lung, 6 (2%) overlapping lung lesion(s), and 4 (1%) main bronchus of the lung. For pancreatic cancer, there were 27 patients (7%) for the head of the pancreas, 10 (3%) pancreas NOS, 9 (2%) body of the pancreas, 9 (2%) tail of the pancreas, 4 (1%) overlapping lesions of the pancreas, 1 (< 1%) pancreatic duct, and 1 (< 1%) other specified parts of the pancreas
There were 342 patients (88%) who were aged > 50 years; 186 male patients (48%) and 201 female patients (52%). There were 293 patients (76%) who had a cancer diagnosis of stage III or IV disease and 94 (24%) who had a cancer diagnosis of stage ≤ II (combination of data for stage 0, 1, and 2, not applicable, and unknown). For their systemic treatment, 161 patients (42%) were treated with erlotinib alone and 226 (58%) received erlotinib concomitantly with additional chemotherapy.
Patients were more likely to discontinue erlotinib for chemotherapy if they received concomitant treatment. Among the patients receiving erlotinib monotherapy, 5% stopped the treatment, whereas 51% of patients treated concomitantly discontinued (P < .001). 
Among the 123 patients who discontinued their treatment, 101 switched treatment with no AEs notes, 22 died or experienced fatigue with blurry vision, constipation, nonspecific gastrointestinal effects, grade-4 diarrhea (as defined by the Common Terminology Criteria for Adverse Events), or developed a pleural fluid, pneumonitis, renal failure, skin swelling and facial rash, and unknown AEs of discontinuation. Patients who discontinued treatment because of unknown AEs had physicians’ notes that detailed emergency department visits, peripheral vascular disease, progressive disease, and treatment cessation, but did not specify the exact symptom(s) that led to discontinuation. The causes of death are unknown because they were not detailed in the available notes or databases. The overall results in this retrospective review cannot establish causality between taking erlotinib or gefitinib and death.
Gefitinib
In September 2021, the Joint Pathology Center provided 33 entries for 33 patients who were systemically treated with gefitinib from January 1, 2002, to December 31, 2017. The patient ages ranged from 49 to 89 years with a mean age of 66 years. There were 31 (94%) and 2 (6%) patients with lung and other cancers, respectively. The upper lobe, lower lobe, and lung NOS had the most patients: 14 (42%), 8 (24%), and 6 (18%), respectively.
There were 31 patients (94%) who were aged > 50 years; 15 were male (45%) and 18 were female (55%). There were 26 patients (79%) who had a cancer diagnosis of stage III or IV disease. Nineteen patients (58%) were treated with gefitinib alone, and 14 (42%) were treated with gefitinib concomitantly with additional chemotherapy. Thirty-one patients (94%) were treated for lung cancer (Table 2). Thirty-three patients are a small sample size to determine whether patients were likely to stop gefitinib if used concomitantly with other drugs. Among the patients treated with gefitinib monotherapy, 5% (n = 1) stopped treatment, whereas 29% (n = 4) of patients treated concomitantly discontinued treatment (P = .06). All comparisons for gefitinib yielded insignificant P values. Physicians’ notes indicated that the reasons for gefitinib discontinuation were life-altering pruritis and unknown (progressive disease outcome) (Table 3).
Management Analysis and Reporting Tool Database
MHS data analysts provided data on diagnoses for 348 patients among 415 submitted, with 232 and 112 patients completing and discontinuing erlotinib or gefitinib treatment, respectively. Each patient had 1 to 104 (completed treatment group) and 1 to 157 (discontinued treatment group) unique health conditions documented. The MHS reported 1319 unique-diagnosis conditions for the completed group and 1266 for the discontinued group. Patients with additional health issues stopped chemotherapy use more often than those without; P < .001 for the completed group (232 patients, 1319 diagnoses) vs the discontinued group (112 patients, 1266 diagnoses). The mean (SD) number of diagnoses was 19 (17) for the completed and 30 (22) for the discontinued treatment groups (Figure).
MHS data was provided for patients who filled erlotinib (n = 240) or gefitinib (n = 18). Among the 258 patients, there were 179 and 79 patients in the completed and discontinued treatment groups, respectively. Each patient filled 1 to 75 (for the completed treatment group) and 3 to 103 (for the discontinued treatment group) prescription drugs. There were 805 unique-filled prescriptions for the completed and 670 for the discontinued group. Patients in the discontinued group filled more prescriptions than those who completed treatment; P < .001 for the completed group (179 patients,805 drugs) vs the discontinued group (79 patients, 670 drugs).
The mean (SD) number of filled prescription drugs was 19 (11) for the completed group and 29 (18) for the discontinued treatment group. The 5 most filled prescriptions with erlotinib from 258 patients with PDTS data were ondansetron (151 prescriptions, 10 recorded AEs), dexamethasone (119 prescriptions, 9 recorded AEs), prochlorperazine (105 prescriptions, 15 recorded AEs), oxycodone (99 prescriptions, 1 AE), and docusate (96 prescriptions, 7 recorded AEs).
Discussion
The difference between erlotinib and gefitinib data can be attributed to the FDA approval date and gefitinib’s association with a higher frequency of hepatotoxicity.18-20 The FDA designated gefitinib as an orphan drug for EGFR mutation–positive NSCLC treatment. Gefitinib first received accelerated approval in 2003 for the treatment of locally advanced or metastatic NSCLC. Gefitinib then was voluntarily withdrawn from the market following confirmatory clinical trials that did not verify clinical benefit.
The current approval is for a different patient population—previously untreated, metastatic EGFR exon 19 or 21 L858R mutation—than the 2003 approval.4,6 There was no record of gefitinib use after 2017 in our study.
Erlotinib is a reversible EGFR-TKI that is approved by the FDA as first-line (maintenance) or second-line treatment (after progression following at least 1 earlier chemotherapy regimen) for patients with metastatic NSCLC who harbor EGFR exon 19 deletions or exon 21 L858R substitution mutations, as detected by an FDA-approved test.3 Since 2005, the FDA also approved erlotinib for first-line treatment of patients with locally advanced, unresectable, or metastatic pancreatic cancer in combination with gemcitabine.3 Without FDA indication, erlotinib is used for colorectal, head and neck, ovarian carcinoma, pancreatic carcinoma, and breast cancer.21
Erlotinib and gefitinib are not considered first-line treatments in EGFR exon 19 or 21–mutated NSCLC because osimertinib was approved in 2018. Targeted therapies for EGFR mutation continue to advance at a fast pace, with amivantamab and mobocertinib now FDA approved for EGFR exon 20 insertion–mutated NSCLC.
Erlotinib Use
Thirty-nine patients (10%) in this study were prescribed erlotinib for off-label indications. Erlotinib was used alone or in combination with bevacizumab, capecitabine, cisplatin, denosumab, docetaxel, gemcitabine, and the MEK-inhibitor selumetinib. Erlotinib combined with cisplatin, denosumab, docetaxel, and gemcitabine had no recorded AEs, with 10 data entries for gemcitabine and 1 for other drugs. Three patients received bevacizumab and erlotinib, and 1 patient (diagnosed with kidney NOS) showed rash or facial swelling/erythema and diffuse body itching then stable disease after 2 cycles.
One patient (diagnosed with cancer located at the pancreas head) was bridged with capecitabine and erlotinib when going on a vacation, then received FOLFIRINOX (a combination chemotherapy regimen containing folinic acid [leucovorin], fluorouracil, irinotecan, and oxaliplatin), which led to significant fatigue, blurry vision, and constipation. One patient was treated for lung NOS with the MEK-inhibitor selumetinib plus erlotinib and developed pneumonitis following treatment.
Because oncologists followed guidelines and protocols in systemic treatment, DDIs of erlotinib concurrently (before or after) and in combination with cancer drugs were unlikely. Further investigation is needed for several 1:1:1 DDIs with noncancer drugs. A retrospective overview is not a randomized clinical study; therefore, analysis is limited. Data from the MHS were obtained solely from notes from physicians who treated the patients; therefore, exact information explaining whether a patient completed treatment or had to withdraw could not be extrapolated (ie, blood/plasma samples were not obtained to confirm).
Discontinued Treatment
The reasons for treatment discontinuation with erlotinib or gefitinib varied among patients, with no consistent AE or cause. Most data were for switching treatments after discontinuing treatment with erlotinib (101 of 123 patients) and gefitinib (2 of 5 patients). This is not surprising given the widely recognized pillars of therapy for NSCLC: chemotherapy, target therapy, and immunotherapy.22 From the MHS records, the reasons patients switched treatment of erlotinib or gefitinib were not listed or listed as due to negative EGFR testing, lack of responsiveness, or enrollment in a different treatment.
Physicians’ notes on AEs were not detailed in most cases. Notes for gastrointestinal effects, life-altering pruritis, intolerance, peripheral vascular disease, pneumonitis, and progressive disease described the change in status or appearance of a new medical condition but did not indicate whether erlotinib or gefitinib caused the changes or worsened a pre-existing condition.
The causes of AEs were not described in the available notes or the databases. This retrospective data analysis only focused on identifying drugs involved with erlotinib and gefitinib treatment; further mapping of DDIs among patients experiencing AEs needs to be performed, then in vitro data testing before researchers can reach a conclusion.
DDIs With Antidepressants
We used the PDTS database to evaluate patients who experienced AEs, excluding patients who switched treatment. Thirteen patients filled a prescription for erlotinib and reported taking 220 cancer and noncancer prescription drugs. One patient (pruritis) was taking gefitinib along with 16 noncancer prescription drugs.
Selective serotonin reuptake inhibitors and other antidepressants have been implicated in CYP 2D6 inhibition and DDIs.48,49 Losartan is a widely used antihypertensive drug with a favorable DDI profile
Our data showed that 16 antidepressants (amitriptyline, bupropion, citalopram, desvenlafaxine, duloxetine, escitalopram, imipramine, fluoxetine, fluvoxamine, mirtazapine, nortriptyline, paroxetine, phenelzine, sertraline, trazodone, and venlafaxine) were recorded with concomitant erlotinib or gefitinib from initiation to completion of therapy or a buffer of 6 months from the first diagnosis date. Based on the date dispensed and days’ supply, only escitalopram could be used in combination with gefitinib treatment. The one patient who filled a prescription for gefitinib and escitalopram completed treatment without recorded AEs. PDTS database confirmed that patients experienced AEs with 5 antidepressants (amitriptyline, mirtazapine, paroxetine, trazodone, and venlafaxine) with concomitant erlotinib use.
Based on the date dispensed and days’ supply, only trazodone could be used in combination with erlotinib. PDTS database showed that cancer drugs (erlotinib and megestrol) and 39 noncancer drugs (including acetaminophen, azithromycin, dexamethasone, hydrocortisone, and polyethylene glycol) were filled by 1 patient whose physician noted skin rash. Another limitation of using databases to reflect clinical practice is that although megestrol is listed as a cancer drug by code in the PDTS database, it is not used for nonendometrial or gynecologic cancers. However, because of the PDTS database classification, megestrol is classified as a cancer drug in this retrospective review.
This retrospective review found no significant DDIs for erlotinib or gefitinib, with 1 antidepressant taken by 1 patient for each respective treatment. The degree of inhibition and induction for escitalopram and trazodone are categorized as weak, minimal, or none; therefore, while 1:1 DDIs might be little or no effect, 1:1:1 combination DDIs could have a different outcome. This retrospective data collection cannot be linked to the in vitro hepatocyte DDIs from erlotinib and gefitinib in previous studies.51,52
Conclusions
This retrospective study describes erlotinib and gefitinib use in the MHS and their potential for DDIs. Because of military service requirements, people who are qualified to serve must be healthy or have either controlled or nonactive medical diagnoses and be physically fit. Consequently, our patient population had fewer common medical illnesses, such as diabetes and obesity, compared with the general population. Most noncancer drugs mentioned in this study are not known CYP metabolizers; therefore, recorded AEs alone cannot conclusively determine whether there is a DDI among erlotinib or gefitinib and noncancer drugs. Antidepressants generally are safe but have boxed warnings in the US for increased risk of suicidal ideation in young people.53,54 This retrospective study did not find statistically significant DDIs for erlotinib or gefitinib with antidepressants. Based on this retrospective data analysis, future in vitro testing is needed to assess DDIs for erlotinib or gefitinib and cancer or noncancer drugs identified in this study.
Acknowledgments
The Department of Research Program funds at Walter Reed National Military Medical Center supported this protocol. We sincerely appreciate the contribution of data extraction from the Joint Pathology Center teams (Francisco J. Rentas, John D. McGeeney, Kimberly M. Greenfield, Beatriz A. Hallo, and Johnny P. Beason) and the MHS database personnel (Maj Ryan Costantino, Lee Ann Zarzabal, Brandon Jenkins, and Alex Rittel). We gratefully thank you for the protocol support from the Department of Research programs: CDR Wesley R. Campbell, CDR Ling Ye, Yaling Zhou, Elizabeth Schafer, Robert Roogow, Micah Stretch, Diane Beaner, Adrienne Woodard, David L. Evers, and Paula Amann.
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12. Nakamura H, Azuma M, Namisato S, et al. A retrospective study of gefitinib effective cases in non-small cell lung cancer patients with poor performance status. J. Clin. Oncol. 2004 22:14_suppl, 8177-8177. doi:10.1200/jco.2004.22.90140.8177
13. Pui C, Gregory C, Lunqing Z, Long LJ, Tou CH, Hong CT. Retrospective analysis of gefitinib and erlotinib in EGFR-mutated non-small-cell lung cancer patients. J Lung Health Dis. 2017;1(1):16-24. doi:10.29245/2689-999X/2017/1.1105
14. Yoshida T, Yamada K, Azuma K, et al. Comparison of adverse events and efficacy between gefitinib and erlotinib in patients with non-small-cell lung cancer: a retrospective analysis. Med Oncol. 2013;30(1):349. doi:10.1007/s12032-012-0349-y
15. Adamo M, Dickie L, Ruhl J. SEER program coding and staging manual 2016. National Cancer Institute; 2016. Accessed June 28, 2023. https://seer.cancer.gov/archive/manuals/2016/SPCSM_2016_maindoc.pdf
16. World Health Organization. International classification of diseases for oncology (ICD-O) 3rd ed, 1st revision. World Health Organization; 2013. Accessed June 28, 2023. https://apps.who.int/iris/handle/10665/96612
17. Z Score Calculator for 2 population proportions. Social science statistics. Accessed April 25, 2023. https://www.socscistatistics.com/tests/ztest/default2.aspx
18. Takeda M, Okamoto I, Nakagawa K. Pooled safety analysis of EGFR-TKI treatment for EGFR mutation-positive non-small cell lung cancer. Lung Cancer. 2015;88(1):74-79. doi:10.1016/j.lungcan.2015.01.026
19. Burotto M, Manasanch EE, Wilkerson J, Fojo T. Gefitinib and erlotinib in metastatic non-small cell lung cancer: a meta-analysis of toxicity and efficacy of randomized clinical trials. Oncologist. 2015;20(4):400-410. doi:10.1634/theoncologist.2014-0154
20. Yang Z, Hackshaw A, Feng Q, et al. Comparison of gefitinib, erlotinib and afatinib in non-small cell lung cancer: a meta-analysis. Int J Cancer. 2017;140(12):2805-2819. doi:10.1002/ijc.30691
21. Mack JT. Erlotinib. xPharm: The comprehensive pharmacology reference, 2007. Accessed June 28, 2023. https://www.sciencedirect.com/topics/chemistry/erlotinib
22. Melosky B. Rapidly changing treatment algorithms for metastatic nonsquamous non-small-cell lung cancer. Curr Oncol. 2018;25(suppl 1):S68-S76. doi:10.3747/co.25.3839
23. Xeloda (capecitabine). Prescribing Information. Hoffmann-La Roche, Genetech; 2015. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2015/020896s037lbl.pdf
24. Paraplatin (carboplatin). Prescribing Information. Bristol-Myers Squibb; 2010. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/020452s005lbl.pdf
25. Gemzar (gemcitabine). Prescribing Information. Eli Lilly and Company; 1996. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/020509s064lbl.pdf
26. Megace (megestrol). Prescribing Information. Par Pharmaceutical, Bristol-Myers Squibb; 2013. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/021778s016lbl.pdf
27. Taxol (paclitaxel). Prescribing Information. BASF Aktiengesellschaft, Bristol-Myers Squibb; 2011. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2011/020262s049lbl.pdf
28. Abraxane (paclitaxel). Prescribing Information. Celgene; 2020. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/021660s047lbl.pdf
29. Alima (pemetrexed). Prescribing Information. Sindan Pharma, Actavis Pharma; 2020. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/208419s000lbl.pdf
30. Tagrisso (Osimertinib). Prescribing Information. AstraZeneca; 2020. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/208065s021lbl.pdf
31. Elavil (amitriptyline). Prescribing Information. Sandoz; 2014. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2014/085966s095,085969s084,085968s096,085971s075,085967s076,085970s072lbl.pdf
32. Lexapro (escitalopram). Prescribing Information. H. Lundbeck, Allergan; 2017. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/021323s047lbl.pdf
33. Remeron (mirtazapine). Prescribing Information. Merck; 2020. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/020415s029,%20021208s019lbl.pdf
34. Paxil (paroxetine). Prescribing Information. Apotex; 2021. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2021/020031s077lbl.pdf
35. Desyrel (trazodone). Prescribing Information. Pragma Pharmaceuticals; 2017. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2017/018207s032lbl.pdf
36. Effexor (venlafaxine). Prescribing Information. Norwich Pharmaceuticals, Almatica Pharma; 2022. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2022/215429s000lbl.pdf
37. Sofran (ondansetron). Prescribing Information. GlaxoSmithKline; 2010. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2010/020007s040,020403s018lbl.pdf
38. Hemady (dexamethasone). Prescribing Information. Dexcel Pharma; 2019. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/211379s000lbl.pdf
39. Levaquin (levofloxacin). Prescribing Information. Janssen Pharmaceuticals; 2020. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/020634s073lbl.pdf
40. Percocet (Oxycodone and Acetaminophen). Prescribing Information. Endo Pharmaceuticals; 2006. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2006/040330s015,040341s013,040434s003lbl.pdf
41. Docusate Sodium usage information. Spirit Pharmaceuticals; 2010. Accessed June 29, 2023. https://dailymed.nlm.nih.gov/dailymed/fda/fdaDrugXsl.cfm?setid=84ee7230-0bf6-4107-b5fa-d6fa265139d0
42. Golytely (polyethylene glycol 3350). Prescribing Information. Sebela Pharmaceuticals; 2020. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/019011s031lbl.pdf
43. Zithomax (azithromycin). Prescribing Information. Pliva, Pfizer; 2013. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2013/050710s039,050711s036,050784s023lbl.pdf
44. Acetaminophen. Prescribing Information. Fresenius Kabi; 2020. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2020/204767s003lbl.pdf
45. Compazine (prochlorperazine). Prescribing Information. GlaxoSmithKline; 2004. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2005/010571s096lbl.pdf
46. Rayos (prednisone). Prescribing Information. Horizon Pharma; 2012. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2012/202020s000lbl.pdf
47. Cortef (hydrocortisone). Prescribing Information. Pfizer; 2019. Accessed June 29, 2023. https://www.accessdata.fda.gov/drugsatfda_docs/label/2019/008697s036lbl.pdf
48. Brown CH. Overview of drug–drug interactions with SSRIs. US Pharm. 2008;33(1):HS-3-HS-19. Accessed June 28, 2023. https://www.uspharmacist.com/article/overview-of-drugdrug-interactions-with-ssris
49. Jin X, Potter B, Luong TL, et al. Pre-clinical evaluation of CYP 2D6 dependent drug-drug interactions between primaquine and SSRI/SNRI antidepressants. Malar J. 2016;15(1):280. doi:10.1186/s12936-016-1329-z
50. Sica DA, Gehr TW, Ghosh S. Clinical pharmacokinetics of losartan. Clin Pharmacokinet. 2005;44(8):797-814. doi:10.2165/00003088-200544080-00003
51. Luong TT, Powers CN, Reinhardt BJ, Weina PJ. Pre-clinical drug-drug interactions (DDIs) of gefitinib with/without losartan and selective serotonin reuptake inhibitors (SSRIs): citalopram, fluoxetine, fluvoxamine, paroxetine, sertraline, and venlafaxine. Curr Res Pharmacol Drug Discov. 2022;3:100112. doi:10.1016/j.crphar.2022.100112
52. Luong TT, McAnulty MJ, Evers DL, Reinhardt BJ, Weina PJ. Pre-clinical drug-drug interaction (DDI) of gefitinib or erlotinib with Cytochrome P450 (CYP) inhibiting drugs, fluoxetine and/or losartan. Curr Res Toxicol. 2021;2:217-224. doi:10.1016/j.crtox.2021.05.006
53. Lu CY, Zhang F, Lakoma MD, et al. Changes in antidepressant use by young people and suicidal behavior after FDA warnings and media coverage: quasi-experimental study. BMJ. 2014;348:g3596. Published 2014 Jun 18. doi:10.1136/bmj.g359654. Friedman RA. Antidepressants’ black-box warning--10 years later. N Engl J Med. 2014;371(18):1666-1668. doi:10.1056/NEJMp1408480
Most cancer treatment regimens include the administration of several chemotherapeutic agents. Drug-drug interactions (DDIs) can increase the risk of fatal adverse events and reduce therapeutic efficacy.1,2 Erlotinib, gefitinib, afatinib, osimertinib, and icotinib are epidermal growth factor receptor–tyrosine kinase inhibitors (EGFR-TKIs) that have proven efficacy for treating advanced non–small cell lung cancer (NSCLC). Erlotinib strongly inhibits cytochrome P450 (CYP) isoenzymes CYP 1A1, moderately inhibits CYP 3A4 and 2C8, and induces CYP 1A1 and 1A2.2 Gefitinib weakly inhibits CYP 2C19 and 2D6.2 CYP 3A4 inducers and inhibitors affect metabolism of both erlotinib and gefitinib.3,4
Erlotinib and gefitinib are first-generation EGFR-TKIs and have been approved for NSCLC treatment by the US Food and Drug Administration (FDA). These agents have been used since the early 2000s and increase the possibility of long-term response and survival.2,5,6 EGFR-TKIs have a range of potential DDIs, including interactions with CYP-dependent metabolism, uridine diphosphate-glucuronosyltransferase, and transporter proteins.2 Few retrospective studies have focused on the therapeutic efficacy of erlotinib, gefitinib,or the combination of these agents.7-14
DDIs from cancer and noncancer therapies could lead to treatment discontinuation and affect patient outcomes. The goals for this study were to perform a broad-scale retrospective analysis focused on investigating prescribed drugs used with erlotinib and gefitinib and determine patient outcomes as obtained through several Military Health System (MHS) databases. Our investigation focused on (1) the functions of these drugs; (2) identifying adverse effects (AEs) that patients experienced; (3) evaluating differences when these drugs are used alone vs concomitantly, and between the completed vs discontinued treatment groups; (4) identifying all drugs used during erlotinib or gefitinib treatment; and (5) evaluating DDIs with antidepressants.
This retrospective study was performed at the Department of Research Programs at Walter Reed National Military Medical Center (WRNMMC) in Bethesda, Maryland. The WRNMMC Institutional Review Board approved the study protocol and ensured compliance with the Health Insurance Portability and Accountability Act as an exempt protocol. The Joint Pathology Center of the US Department of Defense (DoD) Cancer Registry and MHS data experts from the Comprehensive Ambulatory/Professional Encounter Record (CAPER) and the Pharmacy Data Transaction Service (PDTS) provided data for the analysis.
Methods
The DoD Cancer Registry Program was established in 1986 by the Assistant Secretary of Defense for Health Affairs. The registry currently contains data from 1998 to 2023. CAPER and PDTS are part of the MHS Data Repository/Management Analysis and Reporting Tool database. Each observation in the CAPER record represents an ambulatory encounter at a military treatment facility (MTF). CAPER records are available from 2003 to 2023.
Each observation in the PDTS record represents an outpatient prescription filled for an MHS beneficiary at MTFs through the TRICARE mail-order program or a retail pharmacy in the United States. Missing from this record are prescriptions filled at civilian pharmacies outside the United States and inpatient pharmacy prescriptions. The MHS Data Repository PDTS record is available from 2002 to 2023. The Composite Health Care System—the legacy system—is being replaced by GENESIS at MTFs.
Data Extraction Design
The study design involved a cross-sectional analysis. We requested data extraction for erlotinib and gefitinib from 1998 to 2021. Data from the DoD Cancer Registry were used to identify patients who received cancer treatment. Once patients were identified, the CAPER database was searched for diagnoses to identify other health conditions, while the PDTS database was used to populate a list of prescription medications filled during chemotherapy treatment.
Data collected from the Joint Pathology Center included cancer treatment (alone or concomitant), cancer information (cancer types and stages), demographics (sex, age at diagnosis), and physicians’ comments on AEs. Collected data from the MHS include diagnosis and filled prescription history from initiation to completion of the therapy period (or a buffer of 6 months after the initial period). We used all collected data in this analysis. The only exclusion criterion was a provided physician’s note commenting that the patient did not use erlotinib or gefitinib.
Data Extraction Analysis
The Surveillance, Epidemiology, and End Results Program Coding and Staging Manual 2016 and the International Classification of Diseases for Oncology (ICD-O) were used to decode disease and cancer types.15,16 Data sorting and analysis were performed using Microsoft Excel. The percentage for the total was calculated by using the total number of patients or data available within the gefitinib and erlotinib groups divided by total number of patients or data variables. The subgroup percentage was calculated by using the number of patients or data available within the subgroup divided by the total number of patients in that subgroup.
In alone vs concomitant and completed vs discontinued treatment groups, a 2-tailed, 2-sample z test was used to calculate P to determine statistical significance (P < .05) using a statistics website.17 Concomitant was defined as erlotinib or gefitinib taken with other medication(s) before, after, or at the same time as cancer therapy. For the retrospective data analysis, physicians’ notes with “.”, “,”, “/”, “;”, (period, comma, forward slash, semicolon) or space between medication names were interpreted as concurrent, while “+”, “-/+” (plus, minus/plus), or and between drug names were interpreted as combined. Completed treatment was defined as erlotinib or gefitinib as the last medication the patient took without recorded AEs; switching or experiencing AEs was defined as discontinued treatment.
Results
Erlotinib
The Joint Pathology Center provided 387 entries for 382 patients aged 21 to 93 years (mean, 65 years) who were treated systemically with erlotinib from January 1, 2001, to December 31, 2020. Five patients had duplicate entries because they had different cancer sites. There were 287 patients (74%) with lung cancer, 61 (16%) with pancreatic cancer, and 39 (10%) with other cancers. For lung cancer, there were 118 patients (30%) for the upper lobe, 78 (20%) for the lower lobe, and 60 (16%) not otherwise specified (NOS). Other lung cancer sites had fewer patients: 21 (5%) middle lobe lung, 6 (2%) overlapping lung lesion(s), and 4 (1%) main bronchus of the lung. For pancreatic cancer, there were 27 patients (7%) for the head of the pancreas, 10 (3%) pancreas NOS, 9 (2%) body of the pancreas, 9 (2%) tail of the pancreas, 4 (1%) overlapping lesions of the pancreas, 1 (< 1%) pancreatic duct, and 1 (< 1%) other specified parts of the pancreas
There were 342 patients (88%) who were aged > 50 years; 186 male patients (48%) and 201 female patients (52%). There were 293 patients (76%) who had a cancer diagnosis of stage III or IV disease and 94 (24%) who had a cancer diagnosis of stage ≤ II (combination of data for stage 0, 1, and 2, not applicable, and unknown). For their systemic treatment, 161 patients (42%) were treated with erlotinib alone and 226 (58%) received erlotinib concomitantly with additional chemotherapy.
Patients were more likely to discontinue erlotinib for chemotherapy if they received concomitant treatment. Among the patients receiving erlotinib monotherapy, 5% stopped the treatment, whereas 51% of patients treated concomitantly discontinued (P < .001).
Among the 123 patients who discontinued their treatment, 101 switched treatment with no AEs notes, 22 died or experienced fatigue with blurry vision, constipation, nonspecific gastrointestinal effects, grade-4 diarrhea (as defined by the Common Terminology Criteria for Adverse Events), or developed a pleural fluid, pneumonitis, renal failure, skin swelling and facial rash, and unknown AEs of discontinuation. Patients who discontinued treatment because of unknown AEs had physicians’ notes that detailed emergency department visits, peripheral vascular disease, progressive disease, and treatment cessation, but did not specify the exact symptom(s) that led to discontinuation. The causes of death are unknown because they were not detailed in the available notes or databases. The overall results in this retrospective review cannot establish causality between taking erlotinib or gefitinib and death.
Gefitinib
In September 2021, the Joint Pathology Center provided 33 entries for 33 patients who were systemically treated with gefitinib from January 1, 2002, to December 31, 2017. The patient ages ranged from 49 to 89 years with a mean age of 66 years. There were 31 (94%) and 2 (6%) patients with lung and other cancers, respectively. The upper lobe, lower lobe, and lung NOS had the most patients: 14 (42%), 8 (24%), and 6 (18%), respectively.
There were 31 patients (94%) who were aged > 50 years; 15 were male (45%) and 18 were female (55%). There were 26 patients (79%) who had a cancer diagnosis of stage III or IV disease. Nineteen patients (58%) were treated with gefitinib alone, and 14 (42%) were treated with gefitinib concomitantly with additional chemotherapy. Thirty-one patients (94%) were treated for lung cancer (Table 2). Thirty-three patients are a small sample size to determine whether patients were likely to stop gefitinib if used concomitantly with other drugs. Among the patients treated with gefitinib monotherapy, 5% (n = 1) stopped treatment, whereas 29% (n = 4) of patients treated concomitantly discontinued treatment (P = .06). All comparisons for gefitinib yielded insignificant P values. Physicians’ notes indicated that the reasons for gefitinib discontinuation were life-altering pruritis and unknown (progressive disease outcome) (Table 3).
Management Analysis and Reporting Tool Database
MHS data analysts provided data on diagnoses for 348 patients among 415 submitted, with 232 and 112 patients completing and discontinuing erlotinib or gefitinib treatment, respectively. Each patient had 1 to 104 (completed treatment group) and 1 to 157 (discontinued treatment group) unique health conditions documented. The MHS reported 1319 unique-diagnosis conditions for the completed group and 1266 for the discontinued group. Patients with additional health issues stopped chemotherapy use more often than those without; P < .001 for the completed group (232 patients, 1319 diagnoses) vs the discontinued group (112 patients, 1266 diagnoses). The mean (SD) number of diagnoses was 19 (17) for the completed and 30 (22) for the discontinued treatment groups (Figure).
MHS data was provided for patients who filled erlotinib (n = 240) or gefitinib (n = 18). Among the 258 patients, there were 179 and 79 patients in the completed and discontinued treatment groups, respectively. Each patient filled 1 to 75 (for the completed treatment group) and 3 to 103 (for the discontinued treatment group) prescription drugs. There were 805 unique-filled prescriptions for the completed and 670 for the discontinued group. Patients in the discontinued group filled more prescriptions than those who completed treatment; P < .001 for the completed group (179 patients,805 drugs) vs the discontinued group (79 patients, 670 drugs).
The mean (SD) number of filled prescription drugs was 19 (11) for the completed group and 29 (18) for the discontinued treatment group. The 5 most filled prescriptions with erlotinib from 258 patients with PDTS data were ondansetron (151 prescriptions, 10 recorded AEs), dexamethasone (119 prescriptions, 9 recorded AEs), prochlorperazine (105 prescriptions, 15 recorded AEs), oxycodone (99 prescriptions, 1 AE), and docusate (96 prescriptions, 7 recorded AEs).
Discussion
The difference between erlotinib and gefitinib data can be attributed to the FDA approval date and gefitinib’s association with a higher frequency of hepatotoxicity.18-20 The FDA designated gefitinib as an orphan drug for EGFR mutation–positive NSCLC treatment. Gefitinib first received accelerated approval in 2003 for the treatment of locally advanced or metastatic NSCLC. Gefitinib then was voluntarily withdrawn from the market following confirmatory clinical trials that did not verify clinical benefit.
The current approval is for a different patient population—previously untreated, metastatic EGFR exon 19 or 21 L858R mutation—than the 2003 approval.4,6 There was no record of gefitinib use after 2017 in our study.
Erlotinib is a reversible EGFR-TKI that is approved by the FDA as first-line (maintenance) or second-line treatment (after progression following at least 1 earlier chemotherapy regimen) for patients with metastatic NSCLC who harbor EGFR exon 19 deletions or exon 21 L858R substitution mutations, as detected by an FDA-approved test.3 Since 2005, the FDA also approved erlotinib for first-line treatment of patients with locally advanced, unresectable, or metastatic pancreatic cancer in combination with gemcitabine.3 Without FDA indication, erlotinib is used for colorectal, head and neck, ovarian carcinoma, pancreatic carcinoma, and breast cancer.21
Erlotinib and gefitinib are not considered first-line treatments in EGFR exon 19 or 21–mutated NSCLC because osimertinib was approved in 2018. Targeted therapies for EGFR mutation continue to advance at a fast pace, with amivantamab and mobocertinib now FDA approved for EGFR exon 20 insertion–mutated NSCLC.
Erlotinib Use
Thirty-nine patients (10%) in this study were prescribed erlotinib for off-label indications. Erlotinib was used alone or in combination with bevacizumab, capecitabine, cisplatin, denosumab, docetaxel, gemcitabine, and the MEK-inhibitor selumetinib. Erlotinib combined with cisplatin, denosumab, docetaxel, and gemcitabine had no recorded AEs, with 10 data entries for gemcitabine and 1 for other drugs. Three patients received bevacizumab and erlotinib, and 1 patient (diagnosed with kidney NOS) showed rash or facial swelling/erythema and diffuse body itching then stable disease after 2 cycles.
One patient (diagnosed with cancer located at the pancreas head) was bridged with capecitabine and erlotinib when going on a vacation, then received FOLFIRINOX (a combination chemotherapy regimen containing folinic acid [leucovorin], fluorouracil, irinotecan, and oxaliplatin), which led to significant fatigue, blurry vision, and constipation. One patient was treated for lung NOS with the MEK-inhibitor selumetinib plus erlotinib and developed pneumonitis following treatment.
Because oncologists followed guidelines and protocols in systemic treatment, DDIs of erlotinib concurrently (before or after) and in combination with cancer drugs were unlikely. Further investigation is needed for several 1:1:1 DDIs with noncancer drugs. A retrospective overview is not a randomized clinical study; therefore, analysis is limited. Data from the MHS were obtained solely from notes from physicians who treated the patients; therefore, exact information explaining whether a patient completed treatment or had to withdraw could not be extrapolated (ie, blood/plasma samples were not obtained to confirm).
Discontinued Treatment
The reasons for treatment discontinuation with erlotinib or gefitinib varied among patients, with no consistent AE or cause. Most data were for switching treatments after discontinuing treatment with erlotinib (101 of 123 patients) and gefitinib (2 of 5 patients). This is not surprising given the widely recognized pillars of therapy for NSCLC: chemotherapy, target therapy, and immunotherapy.22 From the MHS records, the reasons patients switched treatment of erlotinib or gefitinib were not listed or listed as due to negative EGFR testing, lack of responsiveness, or enrollment in a different treatment.
Physicians’ notes on AEs were not detailed in most cases. Notes for gastrointestinal effects, life-altering pruritis, intolerance, peripheral vascular disease, pneumonitis, and progressive disease described the change in status or appearance of a new medical condition but did not indicate whether erlotinib or gefitinib caused the changes or worsened a pre-existing condition.
The causes of AEs were not described in the available notes or the databases. This retrospective data analysis only focused on identifying drugs involved with erlotinib and gefitinib treatment; further mapping of DDIs among patients experiencing AEs needs to be performed, then in vitro data testing before researchers can reach a conclusion.
DDIs With Antidepressants
We used the PDTS database to evaluate patients who experienced AEs, excluding patients who switched treatment. Thirteen patients filled a prescription for erlotinib and reported taking 220 cancer and noncancer prescription drugs. One patient (pruritis) was taking gefitinib along with 16 noncancer prescription drugs.
Selective serotonin reuptake inhibitors and other antidepressants have been implicated in CYP 2D6 inhibition and DDIs.48,49 Losartan is a widely used antihypertensive drug with a favorable DDI profile
Our data showed that 16 antidepressants (amitriptyline, bupropion, citalopram, desvenlafaxine, duloxetine, escitalopram, imipramine, fluoxetine, fluvoxamine, mirtazapine, nortriptyline, paroxetine, phenelzine, sertraline, trazodone, and venlafaxine) were recorded with concomitant erlotinib or gefitinib from initiation to completion of therapy or a buffer of 6 months from the first diagnosis date. Based on the date dispensed and days’ supply, only escitalopram could be used in combination with gefitinib treatment. The one patient who filled a prescription for gefitinib and escitalopram completed treatment without recorded AEs. PDTS database confirmed that patients experienced AEs with 5 antidepressants (amitriptyline, mirtazapine, paroxetine, trazodone, and venlafaxine) with concomitant erlotinib use.
Based on the date dispensed and days’ supply, only trazodone could be used in combination with erlotinib. PDTS database showed that cancer drugs (erlotinib and megestrol) and 39 noncancer drugs (including acetaminophen, azithromycin, dexamethasone, hydrocortisone, and polyethylene glycol) were filled by 1 patient whose physician noted skin rash. Another limitation of using databases to reflect clinical practice is that although megestrol is listed as a cancer drug by code in the PDTS database, it is not used for nonendometrial or gynecologic cancers. However, because of the PDTS database classification, megestrol is classified as a cancer drug in this retrospective review.
This retrospective review found no significant DDIs for erlotinib or gefitinib, with 1 antidepressant taken by 1 patient for each respective treatment. The degree of inhibition and induction for escitalopram and trazodone are categorized as weak, minimal, or none; therefore, while 1:1 DDIs might be little or no effect, 1:1:1 combination DDIs could have a different outcome. This retrospective data collection cannot be linked to the in vitro hepatocyte DDIs from erlotinib and gefitinib in previous studies.51,52
Conclusions
This retrospective study describes erlotinib and gefitinib use in the MHS and their potential for DDIs. Because of military service requirements, people who are qualified to serve must be healthy or have either controlled or nonactive medical diagnoses and be physically fit. Consequently, our patient population had fewer common medical illnesses, such as diabetes and obesity, compared with the general population. Most noncancer drugs mentioned in this study are not known CYP metabolizers; therefore, recorded AEs alone cannot conclusively determine whether there is a DDI among erlotinib or gefitinib and noncancer drugs. Antidepressants generally are safe but have boxed warnings in the US for increased risk of suicidal ideation in young people.53,54 This retrospective study did not find statistically significant DDIs for erlotinib or gefitinib with antidepressants. Based on this retrospective data analysis, future in vitro testing is needed to assess DDIs for erlotinib or gefitinib and cancer or noncancer drugs identified in this study.
Acknowledgments
The Department of Research Program funds at Walter Reed National Military Medical Center supported this protocol. We sincerely appreciate the contribution of data extraction from the Joint Pathology Center teams (Francisco J. Rentas, John D. McGeeney, Kimberly M. Greenfield, Beatriz A. Hallo, and Johnny P. Beason) and the MHS database personnel (Maj Ryan Costantino, Lee Ann Zarzabal, Brandon Jenkins, and Alex Rittel). We gratefully thank you for the protocol support from the Department of Research programs: CDR Wesley R. Campbell, CDR Ling Ye, Yaling Zhou, Elizabeth Schafer, Robert Roogow, Micah Stretch, Diane Beaner, Adrienne Woodard, David L. Evers, and Paula Amann.
Most cancer treatment regimens include the administration of several chemotherapeutic agents. Drug-drug interactions (DDIs) can increase the risk of fatal adverse events and reduce therapeutic efficacy.1,2 Erlotinib, gefitinib, afatinib, osimertinib, and icotinib are epidermal growth factor receptor–tyrosine kinase inhibitors (EGFR-TKIs) that have proven efficacy for treating advanced non–small cell lung cancer (NSCLC). Erlotinib strongly inhibits cytochrome P450 (CYP) isoenzymes CYP 1A1, moderately inhibits CYP 3A4 and 2C8, and induces CYP 1A1 and 1A2.2 Gefitinib weakly inhibits CYP 2C19 and 2D6.2 CYP 3A4 inducers and inhibitors affect metabolism of both erlotinib and gefitinib.3,4
Erlotinib and gefitinib are first-generation EGFR-TKIs and have been approved for NSCLC treatment by the US Food and Drug Administration (FDA). These agents have been used since the early 2000s and increase the possibility of long-term response and survival.2,5,6 EGFR-TKIs have a range of potential DDIs, including interactions with CYP-dependent metabolism, uridine diphosphate-glucuronosyltransferase, and transporter proteins.2 Few retrospective studies have focused on the therapeutic efficacy of erlotinib, gefitinib,or the combination of these agents.7-14
DDIs from cancer and noncancer therapies could lead to treatment discontinuation and affect patient outcomes. The goals for this study were to perform a broad-scale retrospective analysis focused on investigating prescribed drugs used with erlotinib and gefitinib and determine patient outcomes as obtained through several Military Health System (MHS) databases. Our investigation focused on (1) the functions of these drugs; (2) identifying adverse effects (AEs) that patients experienced; (3) evaluating differences when these drugs are used alone vs concomitantly, and between the completed vs discontinued treatment groups; (4) identifying all drugs used during erlotinib or gefitinib treatment; and (5) evaluating DDIs with antidepressants.
This retrospective study was performed at the Department of Research Programs at Walter Reed National Military Medical Center (WRNMMC) in Bethesda, Maryland. The WRNMMC Institutional Review Board approved the study protocol and ensured compliance with the Health Insurance Portability and Accountability Act as an exempt protocol. The Joint Pathology Center of the US Department of Defense (DoD) Cancer Registry and MHS data experts from the Comprehensive Ambulatory/Professional Encounter Record (CAPER) and the Pharmacy Data Transaction Service (PDTS) provided data for the analysis.
Methods
The DoD Cancer Registry Program was established in 1986 by the Assistant Secretary of Defense for Health Affairs. The registry currently contains data from 1998 to 2023. CAPER and PDTS are part of the MHS Data Repository/Management Analysis and Reporting Tool database. Each observation in the CAPER record represents an ambulatory encounter at a military treatment facility (MTF). CAPER records are available from 2003 to 2023.
Each observation in the PDTS record represents an outpatient prescription filled for an MHS beneficiary at MTFs through the TRICARE mail-order program or a retail pharmacy in the United States. Missing from this record are prescriptions filled at civilian pharmacies outside the United States and inpatient pharmacy prescriptions. The MHS Data Repository PDTS record is available from 2002 to 2023. The Composite Health Care System—the legacy system—is being replaced by GENESIS at MTFs.
Data Extraction Design
The study design involved a cross-sectional analysis. We requested data extraction for erlotinib and gefitinib from 1998 to 2021. Data from the DoD Cancer Registry were used to identify patients who received cancer treatment. Once patients were identified, the CAPER database was searched for diagnoses to identify other health conditions, while the PDTS database was used to populate a list of prescription medications filled during chemotherapy treatment.
Data collected from the Joint Pathology Center included cancer treatment (alone or concomitant), cancer information (cancer types and stages), demographics (sex, age at diagnosis), and physicians’ comments on AEs. Collected data from the MHS include diagnosis and filled prescription history from initiation to completion of the therapy period (or a buffer of 6 months after the initial period). We used all collected data in this analysis. The only exclusion criterion was a provided physician’s note commenting that the patient did not use erlotinib or gefitinib.
Data Extraction Analysis
The Surveillance, Epidemiology, and End Results Program Coding and Staging Manual 2016 and the International Classification of Diseases for Oncology (ICD-O) were used to decode disease and cancer types.15,16 Data sorting and analysis were performed using Microsoft Excel. The percentage for the total was calculated by using the total number of patients or data available within the gefitinib and erlotinib groups divided by total number of patients or data variables. The subgroup percentage was calculated by using the number of patients or data available within the subgroup divided by the total number of patients in that subgroup.
In alone vs concomitant and completed vs discontinued treatment groups, a 2-tailed, 2-sample z test was used to calculate P to determine statistical significance (P < .05) using a statistics website.17 Concomitant was defined as erlotinib or gefitinib taken with other medication(s) before, after, or at the same time as cancer therapy. For the retrospective data analysis, physicians’ notes with “.”, “,”, “/”, “;”, (period, comma, forward slash, semicolon) or space between medication names were interpreted as concurrent, while “+”, “-/+” (plus, minus/plus), or and between drug names were interpreted as combined. Completed treatment was defined as erlotinib or gefitinib as the last medication the patient took without recorded AEs; switching or experiencing AEs was defined as discontinued treatment.
Results
Erlotinib
The Joint Pathology Center provided 387 entries for 382 patients aged 21 to 93 years (mean, 65 years) who were treated systemically with erlotinib from January 1, 2001, to December 31, 2020. Five patients had duplicate entries because they had different cancer sites. There were 287 patients (74%) with lung cancer, 61 (16%) with pancreatic cancer, and 39 (10%) with other cancers. For lung cancer, there were 118 patients (30%) for the upper lobe, 78 (20%) for the lower lobe, and 60 (16%) not otherwise specified (NOS). Other lung cancer sites had fewer patients: 21 (5%) middle lobe lung, 6 (2%) overlapping lung lesion(s), and 4 (1%) main bronchus of the lung. For pancreatic cancer, there were 27 patients (7%) for the head of the pancreas, 10 (3%) pancreas NOS, 9 (2%) body of the pancreas, 9 (2%) tail of the pancreas, 4 (1%) overlapping lesions of the pancreas, 1 (< 1%) pancreatic duct, and 1 (< 1%) other specified parts of the pancreas
There were 342 patients (88%) who were aged > 50 years; 186 male patients (48%) and 201 female patients (52%). There were 293 patients (76%) who had a cancer diagnosis of stage III or IV disease and 94 (24%) who had a cancer diagnosis of stage ≤ II (combination of data for stage 0, 1, and 2, not applicable, and unknown). For their systemic treatment, 161 patients (42%) were treated with erlotinib alone and 226 (58%) received erlotinib concomitantly with additional chemotherapy.
Patients were more likely to discontinue erlotinib for chemotherapy if they received concomitant treatment. Among the patients receiving erlotinib monotherapy, 5% stopped the treatment, whereas 51% of patients treated concomitantly discontinued (P < .001).
Among the 123 patients who discontinued their treatment, 101 switched treatment with no AEs notes, 22 died or experienced fatigue with blurry vision, constipation, nonspecific gastrointestinal effects, grade-4 diarrhea (as defined by the Common Terminology Criteria for Adverse Events), or developed a pleural fluid, pneumonitis, renal failure, skin swelling and facial rash, and unknown AEs of discontinuation. Patients who discontinued treatment because of unknown AEs had physicians’ notes that detailed emergency department visits, peripheral vascular disease, progressive disease, and treatment cessation, but did not specify the exact symptom(s) that led to discontinuation. The causes of death are unknown because they were not detailed in the available notes or databases. The overall results in this retrospective review cannot establish causality between taking erlotinib or gefitinib and death.
Gefitinib
In September 2021, the Joint Pathology Center provided 33 entries for 33 patients who were systemically treated with gefitinib from January 1, 2002, to December 31, 2017. The patient ages ranged from 49 to 89 years with a mean age of 66 years. There were 31 (94%) and 2 (6%) patients with lung and other cancers, respectively. The upper lobe, lower lobe, and lung NOS had the most patients: 14 (42%), 8 (24%), and 6 (18%), respectively.
There were 31 patients (94%) who were aged > 50 years; 15 were male (45%) and 18 were female (55%). There were 26 patients (79%) who had a cancer diagnosis of stage III or IV disease. Nineteen patients (58%) were treated with gefitinib alone, and 14 (42%) were treated with gefitinib concomitantly with additional chemotherapy. Thirty-one patients (94%) were treated for lung cancer (Table 2). Thirty-three patients are a small sample size to determine whether patients were likely to stop gefitinib if used concomitantly with other drugs. Among the patients treated with gefitinib monotherapy, 5% (n = 1) stopped treatment, whereas 29% (n = 4) of patients treated concomitantly discontinued treatment (P = .06). All comparisons for gefitinib yielded insignificant P values. Physicians’ notes indicated that the reasons for gefitinib discontinuation were life-altering pruritis and unknown (progressive disease outcome) (Table 3).
Management Analysis and Reporting Tool Database
MHS data analysts provided data on diagnoses for 348 patients among 415 submitted, with 232 and 112 patients completing and discontinuing erlotinib or gefitinib treatment, respectively. Each patient had 1 to 104 (completed treatment group) and 1 to 157 (discontinued treatment group) unique health conditions documented. The MHS reported 1319 unique-diagnosis conditions for the completed group and 1266 for the discontinued group. Patients with additional health issues stopped chemotherapy use more often than those without; P < .001 for the completed group (232 patients, 1319 diagnoses) vs the discontinued group (112 patients, 1266 diagnoses). The mean (SD) number of diagnoses was 19 (17) for the completed and 30 (22) for the discontinued treatment groups (Figure).
MHS data was provided for patients who filled erlotinib (n = 240) or gefitinib (n = 18). Among the 258 patients, there were 179 and 79 patients in the completed and discontinued treatment groups, respectively. Each patient filled 1 to 75 (for the completed treatment group) and 3 to 103 (for the discontinued treatment group) prescription drugs. There were 805 unique-filled prescriptions for the completed and 670 for the discontinued group. Patients in the discontinued group filled more prescriptions than those who completed treatment; P < .001 for the completed group (179 patients,805 drugs) vs the discontinued group (79 patients, 670 drugs).
The mean (SD) number of filled prescription drugs was 19 (11) for the completed group and 29 (18) for the discontinued treatment group. The 5 most filled prescriptions with erlotinib from 258 patients with PDTS data were ondansetron (151 prescriptions, 10 recorded AEs), dexamethasone (119 prescriptions, 9 recorded AEs), prochlorperazine (105 prescriptions, 15 recorded AEs), oxycodone (99 prescriptions, 1 AE), and docusate (96 prescriptions, 7 recorded AEs).
Discussion
The difference between erlotinib and gefitinib data can be attributed to the FDA approval date and gefitinib’s association with a higher frequency of hepatotoxicity.18-20 The FDA designated gefitinib as an orphan drug for EGFR mutation–positive NSCLC treatment. Gefitinib first received accelerated approval in 2003 for the treatment of locally advanced or metastatic NSCLC. Gefitinib then was voluntarily withdrawn from the market following confirmatory clinical trials that did not verify clinical benefit.
The current approval is for a different patient population—previously untreated, metastatic EGFR exon 19 or 21 L858R mutation—than the 2003 approval.4,6 There was no record of gefitinib use after 2017 in our study.
Erlotinib is a reversible EGFR-TKI that is approved by the FDA as first-line (maintenance) or second-line treatment (after progression following at least 1 earlier chemotherapy regimen) for patients with metastatic NSCLC who harbor EGFR exon 19 deletions or exon 21 L858R substitution mutations, as detected by an FDA-approved test.3 Since 2005, the FDA also approved erlotinib for first-line treatment of patients with locally advanced, unresectable, or metastatic pancreatic cancer in combination with gemcitabine.3 Without FDA indication, erlotinib is used for colorectal, head and neck, ovarian carcinoma, pancreatic carcinoma, and breast cancer.21
Erlotinib and gefitinib are not considered first-line treatments in EGFR exon 19 or 21–mutated NSCLC because osimertinib was approved in 2018. Targeted therapies for EGFR mutation continue to advance at a fast pace, with amivantamab and mobocertinib now FDA approved for EGFR exon 20 insertion–mutated NSCLC.
Erlotinib Use
Thirty-nine patients (10%) in this study were prescribed erlotinib for off-label indications. Erlotinib was used alone or in combination with bevacizumab, capecitabine, cisplatin, denosumab, docetaxel, gemcitabine, and the MEK-inhibitor selumetinib. Erlotinib combined with cisplatin, denosumab, docetaxel, and gemcitabine had no recorded AEs, with 10 data entries for gemcitabine and 1 for other drugs. Three patients received bevacizumab and erlotinib, and 1 patient (diagnosed with kidney NOS) showed rash or facial swelling/erythema and diffuse body itching then stable disease after 2 cycles.
One patient (diagnosed with cancer located at the pancreas head) was bridged with capecitabine and erlotinib when going on a vacation, then received FOLFIRINOX (a combination chemotherapy regimen containing folinic acid [leucovorin], fluorouracil, irinotecan, and oxaliplatin), which led to significant fatigue, blurry vision, and constipation. One patient was treated for lung NOS with the MEK-inhibitor selumetinib plus erlotinib and developed pneumonitis following treatment.
Because oncologists followed guidelines and protocols in systemic treatment, DDIs of erlotinib concurrently (before or after) and in combination with cancer drugs were unlikely. Further investigation is needed for several 1:1:1 DDIs with noncancer drugs. A retrospective overview is not a randomized clinical study; therefore, analysis is limited. Data from the MHS were obtained solely from notes from physicians who treated the patients; therefore, exact information explaining whether a patient completed treatment or had to withdraw could not be extrapolated (ie, blood/plasma samples were not obtained to confirm).
Discontinued Treatment
The reasons for treatment discontinuation with erlotinib or gefitinib varied among patients, with no consistent AE or cause. Most data were for switching treatments after discontinuing treatment with erlotinib (101 of 123 patients) and gefitinib (2 of 5 patients). This is not surprising given the widely recognized pillars of therapy for NSCLC: chemotherapy, target therapy, and immunotherapy.22 From the MHS records, the reasons patients switched treatment of erlotinib or gefitinib were not listed or listed as due to negative EGFR testing, lack of responsiveness, or enrollment in a different treatment.
Physicians’ notes on AEs were not detailed in most cases. Notes for gastrointestinal effects, life-altering pruritis, intolerance, peripheral vascular disease, pneumonitis, and progressive disease described the change in status or appearance of a new medical condition but did not indicate whether erlotinib or gefitinib caused the changes or worsened a pre-existing condition.
The causes of AEs were not described in the available notes or the databases. This retrospective data analysis only focused on identifying drugs involved with erlotinib and gefitinib treatment; further mapping of DDIs among patients experiencing AEs needs to be performed, then in vitro data testing before researchers can reach a conclusion.
DDIs With Antidepressants
We used the PDTS database to evaluate patients who experienced AEs, excluding patients who switched treatment. Thirteen patients filled a prescription for erlotinib and reported taking 220 cancer and noncancer prescription drugs. One patient (pruritis) was taking gefitinib along with 16 noncancer prescription drugs.
Selective serotonin reuptake inhibitors and other antidepressants have been implicated in CYP 2D6 inhibition and DDIs.48,49 Losartan is a widely used antihypertensive drug with a favorable DDI profile
Our data showed that 16 antidepressants (amitriptyline, bupropion, citalopram, desvenlafaxine, duloxetine, escitalopram, imipramine, fluoxetine, fluvoxamine, mirtazapine, nortriptyline, paroxetine, phenelzine, sertraline, trazodone, and venlafaxine) were recorded with concomitant erlotinib or gefitinib from initiation to completion of therapy or a buffer of 6 months from the first diagnosis date. Based on the date dispensed and days’ supply, only escitalopram could be used in combination with gefitinib treatment. The one patient who filled a prescription for gefitinib and escitalopram completed treatment without recorded AEs. PDTS database confirmed that patients experienced AEs with 5 antidepressants (amitriptyline, mirtazapine, paroxetine, trazodone, and venlafaxine) with concomitant erlotinib use.
Based on the date dispensed and days’ supply, only trazodone could be used in combination with erlotinib. PDTS database showed that cancer drugs (erlotinib and megestrol) and 39 noncancer drugs (including acetaminophen, azithromycin, dexamethasone, hydrocortisone, and polyethylene glycol) were filled by 1 patient whose physician noted skin rash. Another limitation of using databases to reflect clinical practice is that although megestrol is listed as a cancer drug by code in the PDTS database, it is not used for nonendometrial or gynecologic cancers. However, because of the PDTS database classification, megestrol is classified as a cancer drug in this retrospective review.
This retrospective review found no significant DDIs for erlotinib or gefitinib, with 1 antidepressant taken by 1 patient for each respective treatment. The degree of inhibition and induction for escitalopram and trazodone are categorized as weak, minimal, or none; therefore, while 1:1 DDIs might be little or no effect, 1:1:1 combination DDIs could have a different outcome. This retrospective data collection cannot be linked to the in vitro hepatocyte DDIs from erlotinib and gefitinib in previous studies.51,52
Conclusions
This retrospective study describes erlotinib and gefitinib use in the MHS and their potential for DDIs. Because of military service requirements, people who are qualified to serve must be healthy or have either controlled or nonactive medical diagnoses and be physically fit. Consequently, our patient population had fewer common medical illnesses, such as diabetes and obesity, compared with the general population. Most noncancer drugs mentioned in this study are not known CYP metabolizers; therefore, recorded AEs alone cannot conclusively determine whether there is a DDI among erlotinib or gefitinib and noncancer drugs. Antidepressants generally are safe but have boxed warnings in the US for increased risk of suicidal ideation in young people.53,54 This retrospective study did not find statistically significant DDIs for erlotinib or gefitinib with antidepressants. Based on this retrospective data analysis, future in vitro testing is needed to assess DDIs for erlotinib or gefitinib and cancer or noncancer drugs identified in this study.
Acknowledgments
The Department of Research Program funds at Walter Reed National Military Medical Center supported this protocol. We sincerely appreciate the contribution of data extraction from the Joint Pathology Center teams (Francisco J. Rentas, John D. McGeeney, Kimberly M. Greenfield, Beatriz A. Hallo, and Johnny P. Beason) and the MHS database personnel (Maj Ryan Costantino, Lee Ann Zarzabal, Brandon Jenkins, and Alex Rittel). We gratefully thank you for the protocol support from the Department of Research programs: CDR Wesley R. Campbell, CDR Ling Ye, Yaling Zhou, Elizabeth Schafer, Robert Roogow, Micah Stretch, Diane Beaner, Adrienne Woodard, David L. Evers, and Paula Amann.
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