Toronto—Pharmacogenetic testing is increasingly a game-changer when it comes to selecting medications for a range of conditions.

In fact, a new Canadian study suggests that it was associated with an 89% increase in remission rates compared with treatment-as-usual (TAU) in patients with treatment-resistant depression (TRD).

The 52-week double-blind study, comparing pharmacogenetic testing-guided treatment to TAU, from the Centre for Addiction and Mental Health (CAMH) in Toronto was published recently in the journal Translational Psychiatry. It is touted as the first-of-its-kind in Canada.

The participants were 276 patients who had been previously diagnosed with TRD; this meant they did not improve after trying at least two antidepressant medications.

"Remission, or full recovery from symptoms, is one of the most challenging endpoints to achieve when treating major depressive disorder," stated senior author James Kennedy, MD, PhD, head of the Tanenbaum Centre for Pharmacogenetics at the Campbell Family Mental Health Research Institute at CAMH. "The findings from this study contribute the first randomized, controlled data in Canada to the growing body of evidence of the clinical value of combined multi-gene pharmacogenetic testing."

Pharmacogenetics uses customized genetic testing, usually with a cheek swab, to help clinicians select appropriate drugs and dosages based on their unique genetic makeup.

Background information in the study pointed out that the pharmacological treatment of depression "consists of stages of trial and error, with less than 40% of patients achieving remission during first medication trial."

The authors noted, however, that in a large, randomized-controlled trial (RCT) in the U.S. called Genomics Used to Improve Depression Decisions (GUIDED), significant improvements in response and remission rates were observed in patients who received treatment guided by combinatorial pharmacogenomic testing.

The Canadian "GAPP-MDD" RCT was a year-long, three-arm, multicenter, participant- and rater–blinded trial that evaluated clinical outcomes among patients with depression whose treatment was guided by combinatorial pharmacogenomic testing compared with TAU. Defined as the outcome was symptom improvement (change in 17-item Hamilton Depression Rating Scale [HAM-D17]) at Week 8. Secondary outcomes included response (>50% decrease in HAM-D17) and remission (HAM-D17 <7) during the same time period.

The researchers found that patients in the guided-care arm had greater symptom improvement (27.6% vs. 22.7%), response (30.3% vs. 22.7%), and remission rates (15.7% vs. 8.3%) compared with TAU, although the differences were not statistically significant. Still, the authors observed that relative improvements in response and remission rates were consistent between the GAPP-MDD (33.0% response, 89.0% remission) and GUIDED (31.0% response, 51.0% remission) trials.

"Together with GUIDED, the results from the GAPP-MDD trial indicate that combinatorial pharmacogenomic testing can be an effective tool to help guide depression treatment in the context of the Canadian healthcare setting," they wrote.

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