Drug interactions with tobacco smoking: An update.
Polycyclic aromatic hydrocarbons in tobacco smoke are believed to be responsible for the induction of cytochrome P450 (CYP) 1A1,
CYP1A2 and possibly CYP2E1. [...] CYP1A2 is a hepatic enzyme responsible for the metabolism of a number of drugs and activation of some procarcinogens.
Caffeine demethylation, using blood clearance or urine metabolite data, has been used as an in vivo marker of CYP1A2 activity, clearly demonstrating an effect of cigarette smoking, CYP2E1 metabolises a number of drugs as well as activating some carcinogens. [...] In animal studies, nicotine induces the activity of several enzymes, including CYP2E1, CYP2A1/2A2 and CYP2B1/2B2, in the brain, but whether this effect is clinically significant is unknown. Similarly, although inhibitory effects of the smoke constituents carbon monoxide and cadmium on CYP enzymes have been observed in vitro and in animal studies, the relevance of this inhibition to humans has not yet been established. The mechanism involved in most interactions between cigarette smoking and drugs involves the induction of metabolism.
Drugs for which induced metabolism because of cigarette smoking may have clinical consequence include theophylline,
caffeine, tacrine, imipramine, haloperidol, pentazocine, propranolol, flecainide and estradiol. [...]