Smoking cessation efficacy and safety of varenicline, an alpha4beta2 nicotinic receptor partial agonist.

BACKGROUND: Varenicline, an alpha4beta2 nicotinic receptor partial agonist, has the potential to relieve nicotine craving and withdrawal symptoms while reducing the reinforcing effects of nicotine. Phase 3 studies have evaluated the effects of varenicline on inducing smoking cessation and maintaining smoking abstinence.

SUBJECTS AND METHODS: Two identically designed randomized, double-blind, smoking cessation studies recruited smokers of 10 or more cigarettes daily who were motivated to quit. Treatment with varenicline 1 mg twice daily was compared with treatment with bupropion 150 mg twice daily or matching placebo for 12 weeks, followed by a 40-week nontreatment observation period. In a third study that investigated maintenance of abstinence, smokers were treated with 12 weeks of open-label varenicline 1 mg twice daily. Subjects who did not smoke during the last week of treatment were eligible to be randomized to varenicline or placebo for an additional 12 weeks, followed by a 28-week nontreatment observation period. Brief smoking cessation counseling was given at clinic visits or telephone contacts scheduled regularly during the entire duration of the 3 studies. Measurement of carbon monoxide in expired breath was used to verify the subjects' reports of nonsmoking.

RESULTS: In the 2 smoking cessation studies, varenicline significantly increased the 4-week continuous abstinence rate during weeks 9 to 12 relative to placebo and bupropion. The continuous abstinence rate during weeks 9 to 52 was also increased compared with placebo and with bupropion (statistically significant in one of the studies). In the maintenance study, smokers who quit after an initial course of open-label varenicline had greater long-term efficacy when they received an additional 12 weeks of varenicline than when they received placebo. In all 3 studies, varenicline was safe and well tolerated, with overall treatment discontinuation rates similar to that of placebo. Nausea was the adverse event that occurred more frequently in subjects receiving varenicline but was mostly mild in intensity.

CONCLUSION: The results of these studies demonstrate a new order of efficacy in medical therapy for smoking cessation. Varenicline proved to be more effective than bupropion in inducing cessation. Furthermore, varenicline prevented relapse in smokers who had progressed toward cessation by quitting for at least 1 week.