Therapeutic drug monitoring in children and adolescents treated with quetiapine for different psychiatric disorders: results of the TDM-VIGIL pharmacovigilance study.

Although quetiapine is increasingly used off-label in children and adolescents with various psychiatric disorders, there is little evidence on the relationship between quetiapine dose and serum concentration, and therapeutic reference ranges (TRR) have not yet been established for this age group. The aim of this study was to evaluate whether the TRR described for adults is applicable to minors. In addition, the study aimed to investigate the relationship between the daily dose, serum concentration and clinical outcome. The clinical course of 77 patients (females = 78%) aged between 12 and 17 years treated with quetiapine in the multicentre pharmacovigilance study TDM-VIGIL was systematically followed, and serum concentrations were measured. A positive mean correlation was observed between the weight-adjusted daily dose and serum concentration (rs = 0.580, p < 0.001). Most patients (84.7%) experienced no ADRs or ADRs not significantly interfering with the patients' functioning. A positive linear relationship between the therapeutic response and serum concentration was found (rs = 0.238, p = 0.006). Only 38.5% of all quetiapine serum concentrations were within the recommended TRR described for adults. Using two different calculation methods, mean ± SD and IQR, our data hinted at considerably lower TRR for minors of about 14-291 ng/ml and 53-234 ng/ml respectively, compared to the suggested TRR for adults. This study has the potential to contribute to the definition of a TRR for quetiapine in minors. However, further controlled studies with larger sample sizes are needed to verify the preliminary results.