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Drug interactions affecting clozapine levels

  • Harvinder Singh (a1), William R. Dubin (a2) and Satinderpal Kaur (a3)


Clozapine is used in combination with psychotropic medication and a wide variety of non-psychotropic medications. This article reviews the literature on clozapine drug interactions and the effect these have on serum level changes in clozapine. A total of 54 articles with a total of 109 individual case reports were obtained by manual and computerised literature search from January 1970 to May 2013. Psychotropic medications most likely to increase clozapine levels include: fluvoxamine, lamotrigine, aripiprazole and the discontinuation of levomepromazine and carbamazepine. Non-psychotropic medications associated with increase in clozapine levels include: erythromycin, ciprofloxacin, omeprazole, cimetidine, OCP containing ethinylestradiol, amiodarone, aluminum hydroxide and isoniazid. Rifampin and St John's wort resulted in low clozapine levels. Smoking cessation also increased clozapine levels. The role of routine clozapine monitoring in clinical practice requires further clarification. In the absence of recommendations for routine clozapine level monitoring, clinical judgment should always be used in addition to diagnostic testing. Clinicians must maintain increased clinical vigilance for adverse side effects when clozapine is combined with other medications.

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Corresponding author

Correspondence to: Dr Harvinder Singh, Department of Psychiatry, Temple University Hospital, Episcopal Campus, MAB Building, 100 East Lehigh Avenue, Philadelphia, PA 19125, USA. E-mail:


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Drug interactions affecting clozapine levels

  • Harvinder Singh (a1), William R. Dubin (a2) and Satinderpal Kaur (a3)


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