Cytisine as a Smoking Cessation Agent: Improving Adherence Through a Better Understanding of Pharmacokinetics and Dose Response

A number of pharmacotherapies are available for smoking cessation in New Zealand including nicotine replacement therapy, bupropion, an antidepressant medication and varenicline. Of these, varenicline is the most effective, but also the most expensive. Varenicline acts like nicotine and stimulates nicotine receptors in the brain, but to a lesser extent, and simultaneously block nicotine binding to its receptors and thus reduces the rewarding effects of cigarette smoking. Cytisine (Tabex® and Desmoxan®) is a plant alkaloid and also acts in a similar way to varenicline but is significantly cheaper. It has been used for more than 50 years in some parts of eastern and central Europe as an aid to quit smoking, but is not approved for use in many countries such as New Zealand, Australia, the UK or the US. Randomised, placebo-controlled trials have shown that cytisine is more effective than placebo and nicotine replacement therapy (NRT)for smoking cessation. However there is a paucity of pre-clinical data on cytisine. In particular, there are limited data on the pharmacokinetic and the dose response characteristics of cytisine. Furthermore, the current dosing regimen recommended by the manufacturer is complex and has no clear basis in empirical research.

Complexity of dosing has been shown to be a key factor in determining adherence. Therefore, a simpler regimen would likely maximise the effectiveness of treatment through improved adherence to the treatment regimen. The investigators therefore propose to undertake two studies to investigate the influence of dose, dosing frequency and dosing duration on the pharmacokinetics and tolerability of cytisine and cigarette craving in smokers.