Pharmacogenetic testing, which is used to classify how patients with major depressive disorder (MDD) metabolize medications, reduces adverse drug-gene interactions, new research shows.
In addition, among the intervention group, the rate of remission over 24 weeks was significantly greater.
“These tests can be helpful in rethinking choices of antidepressants, but clinicians should not expect them to be helpful for every patient,” study investigator David W. Oslin, MD, Corporal Michael J. Crescenz VA Medical Center and professor of psychiatry at Perelman School of Medicine, University of Pennsylvania, Philadelphia, said in an interview.
The findings were published online in JAMA.
Less trial and error
Pharmacogenomic testing can provide information to inform drug selection or dosing for patients with a genetic variation that alters pharmacokinetics or pharmacodynamics. Such testing may be particularly useful for patients with MDD, as fewer than 40% of these patients achieve clinical remission after an initial treatment with an antidepressant, the investigators note.
“To get to a treatment that works for an individual, it’s not unusual to have to try two or three or four antidepressants,” said Dr. Oslin. “If we could reduce that variance a little bit with a test like this, that would be huge from a public health perspective.”
The study included 676 physicians and 1,944 adults with MDD (mean age, 48 years; 24% women) who were receiving care at 22 Department of Veterans Affairs medical centers. Eligible patients were set to start a new antidepressant monotherapy, and all underwent a pharmacogenomic test using a cheek swab.
Investigators randomly assigned patients to receive test results when available (pharmacogenomic-guided group) or 24 weeks later (usual-care group). For the former group, clinicians were asked to initiate treatment when test results were available, typically within 2-3 days. For the latter group, they were asked to initiate treatment on a day of randomization.
Assessments included the 9-item Patient Health questionnaire (PHQ-9), scores for which range from 0-27 points, with higher scores indicating worse symptoms.
Of the total patient population, 79% completed the 24-week assessment.
Researchers characterized antidepressant medications on the basis of drug-gene interaction categories: no known interactions, moderate interactions, and substantial interactions.
The co-primary outcomes were treatment initiation within 30 days, determined on the basis of drug-gene interaction categories, and remission from depression symptoms, defined as a PHQ-9 score of less than or equal to 5.
Raters who were blinded to clinical care and study randomization assessed outcomes at 4, 8, 12, 18, and 24 weeks.
Significant impact?
Results showed that the pharmacogenomic-guided group was more likely to receive an antidepressant that had no potential drug-gene interaction, as opposed to one with a moderate/substantial interaction (odds ratio, 4.32; 95% confidence interval, 3.47-5.39; P < .001).
The usual-care group was more likely to receive a drug with mild potential drug-gene interaction (no/moderate interaction vs. substantial interaction: OR, 2.08; 95% CI, 1.52-2.84; P = .005).
For the intervention group, the estimated rates of receiving an antidepressant with no, moderate, and substantial drug-gene interactions were 59.3%, 30.0%, and 10.7%, respectively. For the usual-care group, the estimates were 25.7%, 54.6%, and 19.7%.
The finding that 1 in 5 patients who received usual care were initially given a medication for which there were significant drug-gene interactions means it is “not a rare event,” said Dr. Oslin. “If we can make an impact on 20% of the people we prescribe to, that’s actually pretty big.”
Rates of remission were greater in the pharmacogenomic-guided group over 24 weeks (OR, 1.28; 95% CI, 1.05-1.57; P = .02; absolute risk difference, 2.8%; 95% CI, 0.6%-5.1%).
The secondary outcomes of response to treatment, defined as at least a 50% decrease in PHQ-9 score, also favored the pharmacogenomic-guided group. This was also the case for the secondary outcome of reduction in symptom severity on the PHQ-9 score.
Some physicians have expressed skepticism about pharmacogenomic testing, but the study provides additional evidence of its usefulness, Dr. Oslin noted.
“While I don’t think testing should be standard of practice, I also don’t think we should put barriers into the testing until we can better understand how to target the testing” to those who will benefit the most, he added.
The tests are available at a commercial cost of about $1,000 – which may not be that expensive if testing has a significant impact on a patient’s life, said Dr. Oslin.