Therapeutic drug monitoring (TDM) — the practice of using laboratory testing to measure blood levels of drugs — has garnered growing interest among rheumatologists in managing patients on disease-modifying antirheumatic drugs (DMARDs), but that hasn’t exactly translated to widespread practice.
While TDM has made some inroads with patients taking monoclonal antibodies, specifically infliximab, its uptake has encountered a number of headwinds, not the least of which is a lack of evidence and clinical guidelines, uneven access and standards of assays, and even an uncertainty about how to interpret laboratory results.
“In some fields, such as neurology, TDM is accepted for antiepileptics,” Michelle Petri, MD, MPH, director of the Johns Hopkins Lupus Center, Baltimore, told Medscape Medical News. “In rheumatology, though, TDM is underutilized and not adequately championed by the American College of Rheumatology.”
Johns Hopkins University
Dr. Michelle Petri
She noted that TDM is most acutely needed for management of systemic lupus erythematosus, where nonadherence is a major problem. “Whole blood hydroxychloroquine monitoring has proven beneficial for identifying nonadherence, but also to pinpoint patients who are on too much, a risk factor for retinopathy,” Petri said.
“The state of therapeutic drug monitoring in general has been interesting when you think about its use in autoimmune disease because it’s very much used in gastroenterology and it’s been much less used in rheumatology,” Zachary Wallace, MD, codirector of the Rheumatology & Allergy Clinical Epidemiology Research Center at Massachusetts General Hospital in Boston, told Medscape Medical News. “Some of that may have to do with the interpretation of the availability of evidence, but I think it’s something clinicians will come across more and more often in their practice and wondering what its role might be,” he added.
Dr. Zachary S. Wallace
The movement to precision medicine also portends to grow interest in TDM in rheumatology, said Stephen Balevic, MD, PhD, a rheumatologist and pharmacologist at Duke University and director of pharmacometrics at the Duke Clinical Research Institute, Durham, North Carolina.
Duke University
Dr. Stephen Balevic
“It’s a very exciting time for rheumatologists to begin thinking outside box on what it means to study precision medicine, and I think pharmacology is one of the most overlooked aspects of precision medicine in our community,” he told Medscape Medical News.
That may be because older DMARDs, namely hydroxychloroquine and methotrexate, came to market when regulatory requirements were different than they are today, Balevic said. “Many of the older conventional DMARDs were discovered incidentally and never really had the traditional pharmacokinetic-pharmacodynamic trials to determine optimal dosing, or perhaps that was extrapolated from other populations,” he said.
So, the “one-size-fits-all” approach does not work for prescribing older or even some of the newer DMARDs for rheumatologic disorders, Balevic said.
Reactive vs Proactive TDM
Among the few trials that examined TDM in rheumatology patients are the NOR-DRUM A and B trials in Norway. Marthe Brun, MD, PhD, a rheumatologist at the Center for Treatment of Rheumatic and Musculoskeletal Diseases at Diakonhjemmet Hospital in Oslo, Norway, and a coauthor of the NOR-DRUM trials, told Medscape Medical News that the trials found an overall benefit to TDM during infliximab maintenance therapy. The trials included not only patients with inflammatory arthritis (rheumatoid arthritis, psoriatic arthritis, and spondyloarthritis) but also patients with inflammatory bowel disease and psoriasis, Brun said.
Nicolas Tourrenc
Dr. Marthe Brun
Brun explained that two types of TDM exist: Reactive and proactive. “Reactive TDM is when you use it to find the reason for a patient having a flare or disease worsening,” she told Medscape Medical News. “Proactive TDM would be regular testing to keep a patient within a therapeutic range to avoid flare because of low drug concentrations.”
Gastroenterologists are more inclined than rheumatologists and dermatologists to use reactive TDM, she said. “There have been no recommendations regarding proactive TDM because of the lack of data.”
In Europe, Wallace noted that European Alliance of Associations for Rheumatology (EULAR) recommendations consider the use of TDM in specific clinical scenarios, such as when treatment fails or to evaluate immunogenicity of a reaction, but they are limited. The American College of Rheumatology (ACR) does not have any recommendations for the use of TDM.
Based on the NOR-DRUM trials, rheumatologists in Norway have published their own guidelines for TDM for infliximab in rheumatologic disease, but they are in Norwegian and have not yet been taken up by EULAR, Brun noted. Publication of those recommendations in English is pending, she said.
“But for other subcutaneously administered TNF inhibitors, there’s a lack of data,” Brun added.
The State of the Evidence
NOR-DRUM A did not support the use of proactive TDM in the 30-week induction period as a way to improve disease remission in patients with chronic immune-mediated inflammatory disease. NOR-DRUM B, which evaluated TDM over a year, found the approach was more likely to lead to sustained disease control for that period.
Brun’s group recently published an analysis of the trials. “We did not find an overall effect during the initial phase of the treatment, the first 30 weeks,” she told Medscape Medical News.
“Then we looked at subgroups, and we found that the patients that developed antidrug antibodies [ADAs] had an effect, and ADA are associated with poorer outcomes as well as infusion reactions for patients treated with infliximab.
“So, it’s probably a benefit to be able to detect these ADA early before the patient experiences a disease flare or infusion reaction,” Brun added. “It facilitates for the clinician to take action to, for example, increase the dosing or switch therapy.”
However, the quality of the data supporting TDM in rheumatology is limited, Balevic said. “There’s very good observational data, but we have very few clinical trials that actually leverage TDM,” he said.
NOR-DRUM is the exception, he said. “Ideally, we need more of these dose-optimization trials to help guide clinical practice,” he said. But it stands alone.
Wallace noted several take-home messages from the NOR-DRUM trials, namely that using TDM to prevent ADA may be more effective during the maintenance phase of treatment than the induction phase. However, he said, the evidence is still emerging.
“It’s reasonable to say that we’re at an early stage of the evidence,” he said. “If you look at the large trials that have been done in rheumatology, they’ve combined patients with many different types of conditions, and a lot of our recommendations in rheumatology are disease-specific — in rheumatoid arthritis, in vasculitis. There’s a lack of data in specific diseases to guide or examine what the role of TDM might be.”
In the meantime, no fewer than four clinical trials evaluating TDM with tumor necrosis factor (TNF) inhibitors in rheumatologic diseases are ongoing or have completed but not yet released results, according to Wallace. Three Adalimumab Drug Optimization in Rheumatoid Arthritis trials are underway: The first is evaluating drug tapering vs disease activity score; the second is testing low or usual drug concentration; and the third is studying switches to etanercept or a non-TNF inhibitor drug (abatacept, rituximab, tocilizumab, or sarilumab) in patients failing treatment. Another trial called Tocilizumab Drug Levels to Optimized Treatment in RA is randomizing patients with high drug levels to dose maintenance or dose reduction. All four trials are sponsored by the Reade Rheumatology Research Institute, Amsterdam, the Netherlands.
Until clearer answers emerge from clinical trials, a number of barriers to and questions about the potential for TDM in rheumatology persist.