Role of nicotine metabolite ratio in pharmacological interventions on smoking cessation: A systematic review and meta-analyses of randomized controlled trials.
BACKGROUND AND OBJECTIVES: Emerging evidence suggests that the nicotine metabolite ratio (NMR) may influence the efficacy of smoking cessation, yet its role across pharmacotherapies remains unclear. This study aims to investigate how NMR affects cessation outcomes under different medications to guide personalized treatment. METHODS: We searched PubMed, Medline, EMBASE, and the Cochrane Central Register of Controlled Trials (inception to September 30, 2024) for randomized controlled trials on pharmacotherapy for smoking cessation with NMR data. Data were synthesized using random-effects models, with heterogeneity assessment. The primary outcome was verified smoking cessation rate at the end of treatment or the closest time-point. RESULTS: Eleven RCTs with accessible full text were included in the qualitative analyses and nine were included in the quantitative synthesis. For non-titratable nicotine replacement therapy (NRT), normal/fast metabolizers demonstrated lower odds of smoking cessation than slow metabolizers (Odds Ratio, OR=0.81, 95% confidence interval, CI=0.68-0.96; 5 studies, I²=62.5%). No significant associations were shown between normal/fast and slow metabolizers using titratable NRT (OR=1.04, 95% CI=0.95-1.14; 2 studies, I²=0%), bupropion (OR=0.67, 95% CI=0.38-1.16; 2 studies, I²=51.4%), or varenicline (OR=1.17, 95% CI=0.79-1.74; 4 studies, I²=59.8%). CONCLUSION: Current evidence demonstrates that NMR moderates' treatment efficacy among those who smoke using non-titratable NRT, with slow metabolizers achieving significantly better cessation outcomes than normal/fast metabolizers. Substantial further research is needed to determine optimal medication hierarchies across metabolic profiles.