Quetiapine Cimetidine

After single-dose administration, the mean bioavailability of quetiapine is 9% with significant interindividual variation. If a CYP 3A4 inhibitor (e.g., cimetidine, ketoconazole, nefazodone, grapefruit juice, or erythromycin) is added to quetiapine, increased side effects (e.g., sedation or orthostasis) may occur. Fluoxetine may also decrease clearance of a medication such as quetiapine metabolized through CYP 3A4. However, with fluoxetine, it is the long-acting metabolite norfluoxetine, and not fluoxetine, that is the primary inhibitor of 3 A4 metabolism. If an enzyme inducer such as carbamazepine or St. lohn s wort is added to quetiapine, then decreased antipsychotic effects may occur. ... 

Quetiapine dose not appear to interact to a clinically relevant extent with cimetidine, fluoxetine, imipramine or lorazepam. Isolated cases of adverse outcomes have been reported with diphenhydramine, iovastatin and mirtazapine. 

Quetiapine 150 mg three times daily was given to 7 psychotic men with cimetidine 400 mg three times daily for 4 days. There were some slight alterations in the pharmacokinetics of the quetiapine, but these were within the intraindividual changes seen and so were not considered significant. There would therefore appear to be no reason for avoiding concurrent use. 

Strakowski SM Keck PE, Wong YWJ, Thyrum PT, Yeh C. The effect of multiple doses of cimetidine on die steady-state pharmacokinetics of quetiapine in men widi selected psychotic disorders. J Clin Psychopharmacol (2002) 22,201 -5. 

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