Serum concentrations of Duloxetine and Clinical Effects

The aim of this study was to relate serum concentrations of duloxetine and clinical effects in patients treated with the new antidepressant. Duloxetine concentrations were measured using a chromatographic method. Assessment of clinical effects comprised the clinical global impressions (CGI) scale and the UKU side effects scale. We analysed 48 serum samples obtained from 29 inpatients with major depression. The patients were treated with 30 to 120mg duloxetine per day and received no other psychotropic medication. Their mean age was 51 years and the mean daily dose was 70mg. The mean steady state serum concentration of duloxetine and the 25th to 75th percentile range were 56ng/ml and 26 to 71ng/ml, respectively. According to CGI 77.5% of the patients improved at least moderately. Receiver operating characteristics analyses revealed significantly more patients who had very much improved when serum concentrations of duloxetine were 65ng/ml or higher than in the group of patients exhibiting lower concentrations of the drug. Only three patients reported mild adverse reactions such as sleepiness or gastrointestinal disturbances which were not associated with high serum concentrations of duloxetine. The data taken together indicate that therapeutic drug monitoring of duloxetine could be helpful for treatment. A duloxetine concentration of 65ng/ml can be assigned as a preliminary lower threshold value for optimal response which needs to be confirmed in a larger patient sample.