Serum concentrations of selective serotonin reuptake inhibitors and atypical antipsychotics in children and adolescents: data from routine clinical care

Therapeutic reference ranges (TRRs) for selective serotonin reuptake inhibitors (SSRIs) and atypical antipsychotics are established for adults. In children and adolescents, however, knowledge on TRRs of psychotropic drugs is scarce. The aim of this study was to determine serum concentrations in children and adolescents to provide guidance for the definition of therapeutic reference ranges in this age group. Within the routine therapeutic drug monitoring service of a German child and adolescent psychiatric university hospital, serum concentrations of citalopram, fluoxetine, fluvoxamine, sertraline, aripiprazole, clozapine, olanzapine, quetiapine or risperidone in children and adolescents were collected between 1999 und 2022 and retrospectively analyzed. The 25th to 75th interquartile ranges (IQRs) were calculated and compared with the TRRs defined for adults. In total, 618 serum level concentrations were examined. The IQRs found for fluvoxamine (75-203 ng/ml), sertraline (25-54 ng/ml), olanzapine (13-57 ng/ml), and aripiprazole (93-245 ng/ml) were similar to published therapeutic ranges for adults. Citalopram (18-51 ng/ml), clozapine (180-419 ng/ml), risperidone plus 9-hydroxyrisperidone (11-35 ng/ml), aripiprazole plus dehydroaripiprazole (118-313 ng/ml) and quetiapine (34-234 ng/ml) exhibit somewhat lower ranges in children and adolescents when compared to adults. The IQR found for fluoxetin (102-263 ng/ml) could not be compared with that of adults due to methodological differences. Our results contribute to the knowledge of serum concentrations of SSRIs and atypical antipsychotics in children and adolescents. The differences found in some substances compared to adults clearly indicate that age- and substance-specific therapeutic ranges need to be defined for children and adolescents.