Clinical effects of a randomized switch of patients from clozaril to generic clozapine

Clozapine was discovered in 1959 but withheld from the United States market after several deaths due to agranulocytosis. The medication was approved in the United States in 1989 on a compassionate-use basis and was first marketed in 1990 as Clozaril. In 1999, following approval by the U.S. Food and Drug Administration, Zenith Goldline Pharmaceuticals (ZGP) introduced a generic form of clozapine.

After 5 weeks of data collection (phase I), 24 patients were randomly assigned to group A and 21 patients to group B. Patients had DSM-IV diagnoses of schizophrenia, schizoaffective disorder, bipolar disorder with psychosis, or atypical psychosis with mood disorder. In phase II, group A received a mean daily dose of 630 mg of generic clozapine, and group B continued to receive Clozaril at a mean daily dose of 610 mg, each for 8 weeks. In phase III, group A was reassigned to Clozaril, and group B was switched to generic clozapine, each for 8 weeks. At the end of phase III, group B resumed Clozaril. Efficacy was measured with the Clinical Global Impressions-Improvement (CGI-I) scale, the Brief Psychiatric Rating Scale (BPRS), and the Beck Depression Inventory (BDI).

Five patients experienced relapse when they were switched from Clozaril to generic clozapine. Eleven patients worsened short of full relapse, 9 while receiving ZGP generic clozapine and 2 while receiving Clozaril. CGI-I scores and BPRS scores favored patients receiving Clozaril significantly. Only BDI scores favored patients receiving generic clozapine significantly.

Until more studies have been performed, clinicians and administrators should carefully monitor stable Clozaril-treated patients who are being switched to generic clozapine.