Objective-This study aimed to examine the effectiveness of quetiapine and the effects of dosage relates to its effectiveness on schizophrenia and schizoaffective disorder in a naturalistic setting in Korean people. Methods-This study was a 24-week, open-label, non-comparative, naturalistic study of quetiapine in patients diagnosed with schizophrenia and schizoaffective disorder according to DSM-IV. We stratified the patients into mild [(clinical global impression severity (CGI-S) <4 at baseline)] and severe groups (CGI-S ≥4 at baseline). We investigated the response rate, defined as clinical global impression improvement (CGI-I) ≤2, in the severe group and the aggravation rate in the mild group using the last-observation-carried-forward (LOCF) and the Kaplan-Meier method (K-M). Results-During the 24 weeks, 151 (18.4%) of the participants dropped out of the study. There was a significant decrease in the mean CGI-S score, from 4.5±1.1 at baseline to 2.8± 1.1 at 24 weeks. The response rate of severe group was 54.5% (estimated by LOCF) and 73.3% (K-M estimated) at 24 weeks. All patients who completed the study had taken a mean quetiapine dosage of 507.9±245.9 mg daily. The decrease of CGI-S score in high-dose group (the maximum dose was 750 mg/d or above) was statistically significant than that in recommendeddose group (the maximum dose was less than 750 mg/d). Conclusion-This study demonstrated the long-term effectiveness of quetiapine in the treatment of schizophrenia and schizoaffective disorder in a naturalistic setting in Korean people. This study suggests that higher than recommended quetiapine dosages could be more effective in some patients.
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