new research suggests.
CYP2D6 and CYP2C19, from the cytochrome P450 family, are involved in the metabolism and elimination of various molecules, including medications. Variants in the genes encoding these enzymes affect the speed at which drugs are metabolized, altering their pharmacokinetic profiles.
The researchers studied 125 patients with MDD and used CYP2D6 and CYP2C19 genotyping to determine the presence of actionable phenotypes in line with Food and Drug Administration labeling.
They found that, in many cases, pharmacogenetic testing could have predicted poor response to the initial treatment selection and could have helped guide subsequent choices to improve outcomes.
In addition, a pharmacoeconomic evaluation that combined direct and indirect costs resulting from MDD with the prevalence of CYP2D6 and CYP2C19 phenotypes showed that testing for functional variants in both genes would be cost effective at a national level.
Had psychiatrists who treated patients in the study known about their metabolizing profiles, it “might have contributed to switches in medication” and could have reduced “delays in response,” said lead researcher Alessio Squassina, PhD, associate professor of pharmacology at the University of Cagliari (Italy).
The findings were presented at the European Psychiatric Association 2022 Congress.
Highly variable response rates
Dr. Squassina noted that the response to antidepressants is a “highly variable trait,” and while it is known that genetics play a role, their contribution is “still not completely understood.”
He explained that the use of pharmacogenetics, which leverages genetic information to guide treatment decision-making, has increased significantly.
While regulatory bodies, including the FDA, have been “very active” in defining strict criteria for interpreting the information from pharmacogenetic tests, there remains some “discrepancy” in their clinical utility.
Dr. Squassina said the FDA provides guidance on use of genetic testing on the labels of 34 psychiatric medications. Of these, 79% relate to CYP2D6, 12% relate to CYP2C19, and 9% relate to other genes.
These labels provide guidance on when genetic testing is recommended or required, as well as potentially clinically actionable gene-drug associations in patients with certain functional alleles.
However, Dr. Squassina noted that the distribution of such alleles is not the same across Europe, so it’s possible that a psychiatrist in Italy may be less likely to treat a patient with a phenotype affecting response to treatment or risk of adverse events than one in Norway or Sweden.
For the study, the investigators examined the frequency of CYP2D6 and CYP2C19 phenotypes in psychiatric patients in Sardinia and their relationship with pharmacologic treatment and cost-effectiveness.
They set out to recruit 200 patients with MDD who had a documented 5-year medical and treatment history, including alterations in treatment, adverse events, hospitalizations, suicide, and symptom scores, as well as sociodemographic variables.
An interim analysis of the first 125 patients recruited to the study showed that the most common CYP2D6 phenotype was normal metabolizers (NM), at 60.5%, followed by intermediate metabolizers (IM), at 28.2%, ultrarapid metabolizers (UR), at 8.9%, and poor metabolizers (PM), at 2.4%.
For CYP2C19, the most common phenotype was NM (49%), followed by IM (29.0%), UR (25.0%), and PM (4.0%). While there were differences in the overall European averages, they were not significant.
To highlight the potential impact that pharmacogenetic testing could have had on patient care and outcome, Dr. Squassina highlighted two cases.
The first concerned a patient with a CYP2D6 IM and CYP2C19 UR phenotype, who did not respond to escitalopram. The FDA drug label indicates this phenotype is actionable and recommends an alternative drug.
The patient was subsequently switched to venlafaxine. The FDA drug label on venlafaxine notes that patients with this phenotype are likely to have a suboptimal response to this drug, and again, this patient did not respond to treatment.
Another patient with a CYP2D6 NM and CYP2C19 IM phenotype was also prescribed escitalopram. The FDA label on this drug notes that patients with this phenotype can try venlafaxine but may not respond. Indeed, this patient did not respond and was switched to venlafaxine and started responding.
“The psychiatrists [in these cases] may made have made different [drug] choices if they had known the genotypes in advance,” Dr. Squassina said.