Delayed respiratory depression after risperidone overdose.

Risperidone is an atypical antipsychotic drug used for the treatment of schizophrenia. Both positive and negative symptoms are prominent with its use. Metabolism occurs mainly in the liver, where risperidone is changed by CUP2D6 to an active metabolite, 9-hydroxyrisperidone. The half-lives of risperidone and its metabolite are 3 and 7 h, respectively. Genetic polymorphism is seen in the 6%-8% of white patients who are considered poor metabolizers. In poor metabolizers, the half-life extends to 20-30 h. We present an unusual case of unanticipated delayed respiratory depression after risperidone overdose.