Evaluation of an Interchangeability Switch in Patients Treated With Clozapine: A Retrospective Review

Objective: To report the findings of a switch from brand-name to generic clozapine in a Canadian outpatient population.

Method: The medical records of 58 outpatients diagnosed with schizophrenia and other psychotic disorders and stabilized on brand-name clozapine therapy were reviewed retrospectively. Patients were switched from brand-name to generic clozapine on their next dispensing supply after September 29, 2003. Data regarding clozapine dose regimens, physicians’ visits, hospitalizations, and adverse events were collected from the patients’ charts for the 6 months preceding and the 6 months after the switch from brand-name to generic clozapine. Relevant measurement changes in those data associated with the switch are evaluated.

Results: No significant changes in dose, number of physician’s visits, or hospitalization rates were observed as a consequence of the switch from brand-name to generic clozapine. In addition, there were no reported increases in the frequency of the most common adverse events, including decreases in white blood cell counts. None of the patients received a “nonrechallengeable” status, and no discontinuation of clozapine therapy occurred for any reason (toxicity or treatment failure) in the 6 months after the formulation switch.

Conclusion: In the current outpatient population, retrospective evaluation of the conversion from brand-name clozapine to the first generic alternative available on the Canadian market did not reveal any significant treatment changes.