Long-Term Response to Clozapine and Its Clinical Correlates in the Treatment of Tardive Movement Syndromes: A Naturalistic Observational Study in Patients With Psychotic Disorders

Purpose Given that switching to clozapine is an important treatment option for tardive movement syndrome (TMS), its effect and clinical correlates have not been fully explored yet. This study investigated the improvement of TMS after switching to clozapine and factors associated with the response in a naturalistic outpatient setting. Methods Subjects were 35 patients with schizophrenia or bipolar disorder receiving only clozapine as an antipsychotic drug for more than 12 months. Their prior antipsychotics were switched to clozapine after the onset of tardive dyskinesia and/or tardive dystonia. Tardive movement syndrome and clinical characteristics were assessed through direct examination and review of hospital records. Findings Offending antipsychotics administered at the time of TMS onset were second-generation antipsychotics in 88.6% of patients. Tardive movement syndrome symptoms were remitted in 65.7% of patients after switching to clozapine. Younger age, younger age at onset of TMS, and lower baseline Abnormal Involuntary Movement Scale score were significantly associated with remission of TMS. Female sex and good antipsychotic effects of clozapine showed a trend of association with better response. Implications Clozapine seems to be an excellent treatment option for TMS in the era of second-generation antipsychotics, especially for younger patients with mild tardive dyskinesia. Clinical trials comparing the effect of switching antipsychotics to clozapine with add-on therapy of new drugs targeting TMS are difficult to design in ordinary clinical settings. Therefore, more naturalistic observational studies are warranted to identify predictors of TMS response to clozapine.