Efficacy of bupropion and varenicline genetic markers in choosing pharmacological treatment for smoking cessation, and implications for combining drugs: A randomized controlled trial - GENTSMOKING.

INTRODUCTION: Smoking cessation is the best strategy for reducing tobacco-related morbimortality. The goal of this randomized controlled trial was to test whether using the genetically favorable markers to choose a smoking cessation drug treatment (precision medicine) was superior to using the most effective drug (varenicline) in terms of abstinence rates. Additionally, combination therapy was tested when monotherapy failed.

METHODS: This partially blind, single-center study randomized (1:1) 361 participants into two major groups. In the genetic group (n=184), CYP2B6 rs2279343 (genotype AA) participants started treatment with bupropion, and CHRNA4 rs1044396 (genotype CT or TT) participants started treatment with varenicline; when genetic favorable to both, participants started treatment with bupropion, and when favorable to neither, on both drugs. In the control group (n=177), participants started treatment with varenicline, regardless of genetic markers. Drug treatment lasted 12 weeks. Efficacy endpoints were abstinence rates at Weeks 4, and Weeks 8-12, biochemically validated by carbon monoxide in exhaled air. Participants who did not achieve complete abstinence at Week 4, regardless of group, were given the choice to receive combination therapy.

RESULTS: Abstinence rates were 42.9% (95% CI: 36-64) in the control group versus 30.4% (95% CI: 23-37) in the genetic group at Week 4 (p=0.01); and 74% (95% CI: 67-80) versus 52% (95% CI: 49-64) at Week 12 (p<0.001), respectively. The strategy of combining drugs after Week 4 increased abstinence rates in both groups and the significant difference between genetic and control groups was maintained.

CONCLUSIONS: Results show that using these selected genetic markers was inferior to starting treatment with varenicline (control group), which is currently the most effective smoking cessation drug; moreover, the addition of bupropion in cases of varenicline monotherapy failure improves the efficacy rate until the end of treatment.

CLINICAL TRIAL IDENTIFIER: NCT03362099.