Is the nicotine metabolite ratio a useful tool to improve the effectiveness, safety, and adherence to quitting smoking? Systematic review of the literature and meta-analysis.

Introduction: We have carried out a systematic review of the literature (SRL) and a meta-analysis (MA) to answer: 1. Validity of the nicotine metabolite ratio (NMR) in improving the effectiveness of pharmacological treatments (PT) for smoking cessation (SC). 2. Validity of the NMR to improve the safety of the use of these PT? and 3. Validity of NMR in improving adherence to these PT?

Method: We carried out an SRL (six databases) and an MA for responding to the questions.

Results: PT for SC (any treatment) is more effective in smoking subjects with slow NMR compared with fast NMR. Varenicline (VR) is equally effective in fast and slow NMR (RR 1.04 [CI 95% 0.75, 1.44]). When we compared those smokers who were treated to quit smoking with VR or nicotine replacement therapy (NRT) in fast metabolizers, we found that abstinence was in favor of those who were treated with VR (RR 1.40 [CI 95% 1.02, 1.91]). Those who were treated to quit smoking with NRT presented better results in slow Metabolizers (RR 0.70 [CI 95% 0.58, 0.83]). NMR increases the safety and adherence of treatments.

Conclusions: We suggest that NMR is a good biomarker in the personalization of smoking cessation.