The effect of coadministration of duloxetine on steady-state serum concentration of risperidone and aripiprazole: a study based on therapeutic drug monitoring data.

Previous studies have categorized duloxetine as a moderate inhibitor of CYP2D6. The aim of the present study was to investigate the potential interactions between duloxetine and the two CYP2D6 substrates risperidone and aripiprazole in psychiatric patients. Serum concentration data from patients treated with risperidone (n = 8) or aripiprazole (n = 7) in combination with duloxetine were retrieved from therapeutic drug monitoring files at the Center for Psychopharmacology, Diakonhjemmet Hospital, Oslo, Norway. The degree of interaction was assessed by comparing the data with a control group of CYP2D6-genotyped patients (homozygous "extensive metabolizers") using oral risperidone or aripiprazole without duloxetine. Coadministration of duloxetine did not significantly increase the concentration of the parent drug or the parent drug/metabolite ratio of either risperidone or aripiprazole. The present study therefore indicates that duloxetine may safely be used concomitantly with risperidone or aripiprazole.