Smoking and drug interactions

Abstract

When patients enter hospital they may have to stop smoking abruptly if the hospital has a 'no smoking' policy. Abrupt smoking cessation can affect the metabolism of drugs. Cigarette smoking induces the activity of human cytochromes P450 (CYP) 1A2 and 2B6. These enzymes metabolise several clinically important drugs, including clozapine, olanzapine and methadone. Decreased CYP1A2 activity after smoking cessation increases the risk of adverse drug reactions, with reports of increased toxicity from clozapine and olanzapine. Predicting the required dose reduction of drugs metabolised by CYP1A2 after smoking cessation is challenging. Therapeutic drug monitoring should be used when possible. Nicotine replacement therapy does not influence CYP1A2 activity.