BACKGROUND: The authors attempted to determine if chronic exposure to clozapine can cause tardive dyskinesia. METHOD: Twenty-eight schizophrenic or schizoaffective patients with no prior history of definite tardive dyskinesia were treated with clozapine for at least 1 year, and their ongoing modified Simpson Dyskinesia Scale ratings were analyzed. These data were then compared with those of another group of similarly diagnosed patients who were treated with a conventional neuroleptic for at least 1 year. RESULTS: Two patients in the clozapine-treated group (both of whom had ratings of questionable tardive dyskinesia at baseline) were later rated by the modified Simpson Dyskinesia Scale as having mild tardive dyskinesia on at least two consecutive ratings 3 months apart. Although there was uncertainty about whether clozapine definitely caused the tardive dyskinesia in those two patients, a survival analysis comparing the clozapine-treated group with the neuroleptic-treated group showed a lower risk of tardive dyskinesia developing in the clozapine-treated group. CONCLUSION: This study was unable to definitively conclude whether clozapine causes tardive dyskinesia. However, if cases do develop, the risk of tardive dyskinesia is likely to be less with clozapine than with typical neuroleptics.
BACKGROUND: The authors attempted to determine if chronic exposure to clozapine can cause tardive dyskinesia. METHOD: Twenty-eight schizophrenic or schizoaffective patients with no prior history of definite tardive dyskinesia were treated with clozapine for at least 1 year, and their ongoing modified Simpson Dyskinesia Scale ratings were analyzed. These data were then compared with those of another group of similarly diagnosed patients who were treated with a conventional neuroleptic for at least 1 year. RESULTS: Two patients in the clozapine-treated group (both of whom had ratings of questionable tardive dyskinesia at baseline) were later rated by the modified Simpson Dyskinesia Scale as having mild tardive dyskinesia on at least two consecutive ratings 3 months apart. Although there was uncertainty about whether clozapine definitely caused the tardive dyskinesia in those two patients, a survival analysis comparing the clozapine-treated group with the neuroleptic-treated group showed a lower risk of tardive dyskinesia developing in the clozapine-treated group. CONCLUSION: This study was unable to definitively conclude whether clozapine causes tardive dyskinesia. However, if cases do develop, the risk of tardive dyskinesia is likely to be less with clozapine than with typical neuroleptics.