Cross-titration from risperidone to clozapine utilizing clozapine serum concentrations: A case report.

Introduction: Clozapine and risperidone are second-generation antipsychotics used in the treatment of schizophrenia. There are no guidelines on cross-titration of antipsychotics and, additionally, there is a paucity of published data to support the potential utility of using serum drug levels to guide dosing in these situations.

Case report: A 68-year-old female patient with a history of schizophrenia, taking risperidone and fluoxetine, and a recent diagnosis of Parkinson's disease was admitted to the hospital after a fall at home. During the patient's hospital stay, utilizing serum clozapine levels as guidance, the patient was cross-titrated from risperidone 12 mg daily to a final dose of clozapine 75 mg daily over the span of 17 days, in the setting of multiple possible drug-drug interactions.

Discussion: There is no evidence-based guidance on transitioning patients from one antipsychotic to another especially in the setting of drug-drug interactions. In this case, the patient was successfully transitioned from risperidone to clozapine using serum clozapine levels and clinical status to guide decision-making.

Conclusions: Utilizing serum clozapine levels may be helpful in guiding dose changes during antipsychotic cross-titration, especially when multiple drug interactions are involved.