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Objective: The aim of this study was to investigate the effectiveness, tolerability, and safety of quetiapine in adolescents with schizophrenia, schizophreniform, and schizoaffective disorders in a prospective open-label study.

Method: A total of 56 subjects (all-subjects-treated, AST), ages 12–17, received 200–800 mg of quetiapine per day (forced titration to 400 mg within week 1; median study dose 600 mg/day at week 6) in Germany, 2002 through 2004. Primary outcome measure was the change of Positive and Negative Syndrome Scale (PANSS) total score (based on the intent-to-treat (ITT) population, n = 52), secondary outcome measures were changes of PANSS subscales, severity of illness, subjective wellbeing, and safety/tolerability (the latter based on the AST population). Correlates of PANSS response (=50% reduction in PANSS total score) and discontinuation due to lack of effectiveness were analyzed by Cox regression analyses.

Results: Twenty seven subjects (48%) completed the study; 17 subjects (30%) were discontinued due to lack of effectiveness. A significant reduction of PANSS total score (last observation carried forward, LOCF; p < 0.0001; effect size = 0.92) and of secondary effectiveness outcomes were detected. In all, 34.6% fulfilled the PANSS response criterion, correlated with the degree of PANSS total change within week 1. Somnolence (21.4%) and fatigue (17.9%) were the most frequent adverse events. A significant mean weight gain (6.2 kg) and mean decrease in total serum thyroxine (2.5 ng/dl) were detected.

Conclusions: In this sample of mostly drug-naïve patients with early-onset schizophrenia spectrum disorders, significant reductions in PANSS total and positive scores were detected. Controlled studies are needed to confirm these findings. The significant weight gain with its potentially severe medical consequences must be weighed against quetiapine's effectiveness.