Therapeutic Drug Monitoring in Children and Adolescents Under Pharmacotherapy With Olanzapine in Daily Clinical Practice.

Background: The relationship between daily dose, serum concentrations, and clinical outcomes of olanzapine as well as the influencing factors thereof in children and adolescents treated for different psychiatric disorders were investigated in daily clinical practice. In addition, it was examined whether the current recommended therapeutic range (TR) for adult patients with psychotic disorders is valid for minors.

Methods: The Competence Network for Therapeutic Drug Monitoring (www.tdm-kjp.com) routinely collects demographic and clinical outcome data as well as serum concentrations of children and adolescents treated with psychotropics. The therapeutic effect is documented using the Clinical Global Impression Scale subscale for Global Improvement. Adverse drug reactions (ADRs) are assessed using the Udvalg for Kliniske Undersogelser-Side Effect Rating Scale.

Results: One hundred fifteen patients (mean age = 15.9 years; range = 10.4-18.8 years; 40.9% male) were included. The majority (72.1%) was cotreated with other psychotropic drugs. A positive medium linear relationship (r = 0.619; P < 0.001) between olanzapine dose (mean = 11.64 mg/d) and serum concentration (mean = 35.65 ng/mL) was found with a marked interindividual variability of serum concentrations. Neither relationship between olanzapine serum concentration and treatment response (clinical benefit documented in 80%) nor ADRs (documented in 53.3%, in 7.5% judged as severe) was detected. Most of the patients with psychotic and eating disorders (68.8% and 71.8%, respectively) had an olanzapine serum concentration within the TR suggested for adults.

Conclusions: There are several limitations of this study because of the naturalistic design, and our results should therefore be interpreted with caution. As most of the patients showed a clinical benefit under olanzapine concentrations within the TR for adults and only a minority had severe ADRs, it is reasonable to conclude a similar TR for children, adolescents, and adults.