The effects of the atypical antipsychotics clozapine, remoxipride and risperidone on the contractile characteristics of rat skeletal muscle in vitro.

The therapeutic use of the atypical antipsychotics clozapine, remoxipride and risperidone has been reported to be associated with a reduced occurrence of the extrapyramidal side-effects seen during therapy with classical (or typical) antipsychotics such as trifluoperazine and haloperidol. The aim of this study was to determine the effects of the atypical antipsychotics clozapine, remoxipride and risperidone on rat skeletal muscle in vitro. Remoxipride and risperidone did not produce contracture in muscle. Clozapine induced a small muscle contracture at high concentrations. Pre-treatment of muscle with trifluoperazine or haloperidol in vitro caused the muscle to display contracture responses to halothane, and haloperidol also potentiated a contracture response to caffeine. Pre-treatment of muscle with remoxipride and risperidone did not induce contracture in response to halothane and did not potentiate caffeine contracture. Clozapine pre-treatment caused muscle fibre bundles to display a small halothane-induced contracture and caused significant potentiation of caffeine-induced contracture.