Therapeutic Drug Monitoring of Children and Adolescents Treated with Fluoxetine

Introduction: Information about therapeutic serum levels of fluoxetine (FLX) and its major metabolite norfluoxetine (NORFLX) in children and adolescents is scarce. Methods: Therapeutic drug monitoring (TDM) of FLX was routinely performed in 71 subjects treated for a major depressive disorder (MDD) (10-60 mg/d FLX, median: 20 mg/d). Correlations between serum concentration and dosage, age, gender, smoking habits and adverse events were analysed. Results: Serum concentrations of the active moiety (FLX + NORFLX) ranged from 21 to 613 ng/mL mean concentration of 213 +/- 118 ng/mL, median: 185 ng/mL). High inter-individual variability in serum concentrations of the active moiety of FLX at each dosage level was observed and no relationship between serum concentration and clinical outcome was found. Apart from smoking, none of the factors tested had a significant effect on the serum concentration. Discussion: It was shown that serum concentrations of the active moiety of FLX in children and adolescents seem to be similar to those in adults, with a high level of inter-individual variation. The proportion of patients who showed benefits from treatment with a dose of 20 mg/d FLX was high.