Relation between dosage, serum concentration and therapeutic response of quetiapine in children and adolescents with different psychiatric disorders in clinical practice

Introduction: Quetiapine is used frequently in the treatment of children and adolescents with different psychiatric disorders despite not being licensed for this age group. The aim of this observational study was to examine the relationship between dosage, serum concentration and therapeutic response in children and adolescents treated with quetiapine in daily clinical practice. Methods: Steady state trough serum concentrations of quetiapine were measured in 122 children and adolescents as part of a routine TDM-program. The therapeutic effect was assessed by the Clinical Global Impression Improvement subscale (CGI-I) and side effects by the Udvalg for Kliniske Undersogelser-side effect rating scale (UKU). Results: A weak linear relationship between the bodyweight adjusted daily dose (mean (SD); 6.1 (4.1)mg/kg) and serum concentration (mean (SD); 78.5 (93.1) ng/ml) of quetiapine was found (Pearson r²=0.13). The majority (77.9%) of the measured serum concentrations were below, 20.5% within and 1.6% above the therapeutic window (100–500ng/ml) suggested for adults. Serum concentrations were not significantly influenced by gender, smoking-habits or co-medication. 43% of the patients showed very good or good improvement, 48% little improvement, 7% no change and only 2% deteriorated. 45.1% of the patients had side effects; most of them mild. However, no correlation between serum concentration and neither the therapeutic nor side effects was found. Discussion: Our results suggest a lower therapeutic window of quetiapine for children and adolescents and higher dosing than in adult psychiatric patients. Further studies with greater sample sizes and diagnosis-specific as well as age-specific psychometric instruments are needed to confirm our findings.