If you are trying to quit smoking, knowing the rate at which your body metabolizes nicotine may be the key to success, according to new research from the University of Toronto. The study findings may eventually lead to personalized cessation treatments which could significantly improve success rates.
The key is in determining how long nicotine remains in a smoker’s body between cigarettes and after quitting smoking. There are two general types: normal metabolizers and slow metabolizers.
In normal metabolizers, nicotine levels drop more quickly, putting them at risk for stronger cravings and relapse. Normal metabolizers are more likely to be helped by medications such as varenicline (brand name Champix) which can increase levels of the “feel-good” hormone dopamine and therefore lower cravings.
Normal metabolizers have much greater success after treatment with varenicline compared to the nicotine patch, both at the end of treatment and six months later.
Slow metabolizers of nicotine, however, benefit more from the nicotine patch, say the researchers. Although varenicline is just as effective as the patch for slow metabolizers, it causes more negative side effects.
“In this new trial, we’ve shown that it is possible to optimize quit rates for smokers, while minimizing side effects, by selecting treatment based on whether people break down nicotine slowly or normally,” said Dr. Rachel Tyndale, a professor of pharmacology and toxicology and psychiatry at the university and a senior scientist at the Centre for Addiction and Mental Health’s Campbell Family Mental Health Research Institute.
For the study, 1,246 smokers who were trying to quit were categorized as either slow metabolizers (662 participants) or normal metabolizers (584). They were randomized to receive one of the following for 11 weeks: the nicotine patch plus a placebo pill; varenicline plus placebo patch; or both placebo pill and patch.
All participants received behavioral counseling. The trial was conducted at four academic medical centers.
Smokers’ status as either a normal or slow metabolizer was based on a measure called the nicotine metabolite ratio (NMR). NMR is the ratio of two chemical products of nicotine, which break down at different rates based on different genetic versions of CYP2A6, a liver enzyme.
Participants’ smoking behavior was analyzed at the end of treatment, and six and 12 months later.
Among normal metabolizers, nearly 40 percent taking varenicline were still not smoking at the end of treatment, compared to 22 percent on the nicotine patch. The quit rates, as expected based on the difficulty of prolonged quitting success, decreased at six and 12 months, but the general pattern of response for both normal and slow metabolizers on the patch and varenicline remained.
“This is a much-needed, genetically-informed biomarker that could be translated into clinical practice,” said Caryn Lerman, Ph.D., professor of psychiatry and director of the Center for Interdisciplinary Research on Nicotine Addiction at the University of Pennsylvania.
“Matching a treatment choice based on the rate at which smokers metabolize nicotine could be a viable strategy to help guide choices for smokers and ultimately improve quit rates.”
At this time, there are no commercial tests for this biomarker, so right now smokers and their doctors have no way of knowing which cessation treatment will work best.
Tyndale is hopeful that the findings will lead to the development of such a test, as it would help raise treatment success for all smokers without unnecessarily exposing them to a drug which doesn’t work as well, or has avoidable side effects.
The study published is published in The Lancet Respiratory Medicine.
Source: University of Toronto