Lack of drug interactions between mirtazapine and risperidone in psychiatric patients: a pilot study

An open-label, non-randomized, pilot study has been performed in inpatients in need of treatment with an antipsychotic (risperidone) and an antidepres sant (mirtazapine) with the objective to preliminarily assess a possible ph armacokinetic interaction and the tolerability of this combination. A 1-4-w eek single drug treatment phase (risperidone 1-3 mg bid or mirtazapine 30 m g nocte) was followed by a 2-4-week combined drug treatment phase at unchan ged doses. Twelve patients were enrolled, nine of whom were treated with ri speridone in the single drug phase. Results of plasma level measurements ar e available for six patients and indicate that adding mirtazapine to risper idone does not alter steady-state plasma concentrations of risperidone and its 9-hydroxy metabolite. Data from one patient suggest that adding risperi done to mirtazapine does not result in clinically relevant changes in plasm a concentrations of either compound. The combination was well tolerated and no major or relevant adverse events were observed. Adding risperidone to m irtazapine probably does not necessitate a change of the dosage of either d rug, but more extensive investigations are needed. (C) 1999 Elsevier Scienc e B;V. All rights reserved.