No effect of citalopram on plasma levels of clozapine, risperidone and their active metabolites in patients with chronic schizophrenia

Objective: The effect of citalopram on steady-state plasma concentrations of the newer antipsychotics clozapine and risperidone was studied in 15 schizophrenic patients with residual negative symptoms. Methods: Eight patients stabilised on clozapine therapy (200 to 400 mg/day) and seven on risperidone (4 to 6 mg/day) received additional citalopram (40 mg/day) for 8 consecutive weeks. Results: There were no significant changes in plasma concentrations of clozapine, risperidone and their active metabolites during the study period, suggesting that citalopram does not affect their metabolism. An improvement in negative symptomatology, as measured by the Scale for Assessment of Negative Symptoms, was observed in two patients in each group and the drug combination was well tolerated. Conclusion: While controlled studies are needed to evaluate the clinical benefits of citalopram in chronic schizophrenia, our findings indicate that citalopram may be added to the therapy of patients on maintenance treatment with clozapine or risperidone.