Objective: To examine the pharmacokinetic implications and potential clinical effects of tobacco smoking cessation in patients on stable clozapine or olanzapine treatment.
Data sources: A literature search of MEDLINE (1950-November 2009) and EMBASE (1980-November 2009) was conducted using the search terms smoking, tobacco, cigarette, cannabis, smoking cessation, cytochrome P450, antipsychotic, clozapine, and olanzapine. In addition, reference lists from publications identified were searched manually.
Study selection and data extraction: English-language articles and human studies were identified, yielding 111 returns. Articles that reported clinical outcomes following smoking cessation were selected. Pharmacokinetic data for these drugs were reviewed and articles that provided relevant background information were also included.
Data synthesis: Pharmacokinetic studies have demonstrated more rapid clearance of olanzapine and lower clozapine and norclozapine (desmethylclozapine) concentrations in smokers compared to nonsmokers. These studies also found that smokers require higher doses of these agents than nonsmokers. There are case reports of adverse clinical outcomes following smoking cessation in patients being treated with olanzapine and clozapine. Reports that included serum concentrations consistently found elevations following smoking cessation, and dosage reductions of 30-40% were required to achieve pre-cessation concentrations. Worsening psychiatric symptoms, somnolence, hypersalivation, extreme fatigue, extrapyramidal effects, and seizures have all been reported following smoking cessation in this patient group.
Conclusions: Pharmacists need to be aware of potential risks associated with smoking cessation in patients stabilized on clozapine or olanzapine. Toxicity as a result of recent smoking reduction or cessation may be a reason for hospital admission. For hospitalized patients, pharmacists should obtain information concerning smoking status, including cessation attempts. Nonspecific signs and symptoms of elevated clozapine or olanzapine concentrations should be considered in relation to clinical status while the patient is hospitalized. Measurement of baseline serum clozapine concentrations and/or empiric dosage adjustment in patients expected to have a prolonged hospital stay with forced smoking cessation may be appropriate.