Aims: Nicotine nasal spray and transdermal nicotine are effective aids to smoking cessation, and are being evaluated for treatment of other medical diseases. Wide variation in levels of nicotine and its metabolite, cotinine, have been observed with such therapies. This study aimed primarily to assess sources of individual variability in nicotine and metabolite plasma levels from these dosing systems and from cigarette smoking.
Methods: Twelve cigarette smokers, studied on a clinical research ward, received four treatments of 5 days duration each, including (1) cigarette smoking, 16 cigarettes/day; (2) transdermal nicotine, 15 mg/day; (3) nicotine nasal spray, 24-1 mg doses/day; (4) placebo nicotine nasal spray, 24 doses/day. On a different occasion, the disposition kinetics of nicotine and cotinine were determined via infusion of deuterium-labeled nicotine and continine. Plasma levels of nicotine, cotinine, and 3'-hydroxycotinine and daily intake of nicotine during various treatments were examined, as well as pharmacokinetic factors that determined plasma nicotine and continine levels.
Results: There was considerable individual variation in plasma nicotine and cotinine levels and in the daily of nicotine absorbed from various delivery systems, with most variability with nicotine nasal spray (fivefold) and least for transdermal nicotine (two-to threefold). Plasma nicotine levels were determined most strongly by nicotine clearance. Continine levels were determined most strongly by dose of nicotine and, to a lesser extent, the clearance of cotinine and fractional conversion of nicotine to continine.
Conclusions: Plasma levels of nicotine and cotinine produced by nicotine therapies are highly variable, due to both wide variability in individual pharmacokinetics and in dose delivery from the products. To compensate for individual differences in clearance, individualization of nicotine dosing based on therapeutic drug monitoring with comparison to nicotine or continine levels during cigarette smoking prior to treatment may be necessary to optimize nicotine therapy. This study also validates a recently proposed method for estimating absolute bioavailability of a drug using drug and metabolite pharmacokinetic data, and presents novel data on plasma levels of the metabolite trans-3'-hydroxycotinine in people.