Retrospective evaluation of the effect of omeprazole on clozapine metabolism.

Objective: To study the effect of the replacement of omeprazole by pantoprazole on clozapine metabolism in 13 psychiatric patients, who used both clozapine and omeprazole.

Method: Retrospective study of the medical files.

Results: In comparison to smokers, a significant rise of the serum clozapine levels was observed in all non-smoking patients, whilst the daily dose of clozapine remained unchanged. This effect was probably caused by the discontinuation of enzyme induction of the cytochrome P450 enzyme 1A2 by omeprazole in non-smokers, whereas CYP1A2 remained induced in patients who smoked.

Conclusion: Omeprazole only influenced clozapine metabolism in non-smokers. In none of the patients an adjustment of the clozapine dose was required.