Relationship Between Daily Dose, Serum Concentration, and Clinical Response to Quetiapine in Children and Adolescents with Psychotic and Mood Disorders.

In child and adolescent psychiatry, therapeutic drug monitoring (TDM) is strongly recommended. However, therapeutic ranges (TR) are defined only for adults. The objectives of this naturalistic study were to assess the relationships between serum quetiapine concentration, daily dose, and clinical outcomes as well as the determinants of pharmacokinetic variability. Furthermore, it was elucidated whether the recommended TR for adult patients with psychotic disorders is valid for children and adolescents. TDM was performed in 180 pediatric patients treated with quetiapine. Psychopathological changes were assessed by the Clinical Global Impression - Improvement scale (CGI-I). Adverse drug reactions (ADRs) were assessed by using a short form of the Udvalg for Kliniske Undersogelser (UKU) side effect rating scale. A weak positive linear relationship between daily dose (mean 349.9±248.9 mg/day) and serum concentration of quetiapine (r=0.496, p<0.001) was found (mean age 15.6±1.9 years, 45.6% male, 31.1% monotherapy), but no relationship between serum concentration and clinical outcome was found. Dose variation accounted for only 12.5% (r=0.125) of the variability of serum concentrations. No effects by gender, age, body weight, smoking habits, and co-medication were found. The majority of patients with psychotic (67.8%) and mood disorders (74.5%) showed a serum concentration below the suggested lower limit (100 ng/mL) of the TR for adults. There are several limitations of this study because of the naturalistic design, and our results should therefore be interpreted with caution. Notwithstanding, our data suggest that the lower limit of the TR for quetiapine is lower than the limit in adult patients.