Japan approved clozapine for treatment-resistant schizophrenia in June 2009. The aim of this study was to evaluate clozapine's efficacy and tolerability in Japanese patients. A twelve-week, single-arm clinical trial of clozapine in treatment-resistant schizophrenia inpatients, was conducted under real-world conditions using raters masked for type of antipsychotic. Thirty-eight patients were recruited, with 33 (86.8%) completing the trial. At week 12, clozapine was associated with significant improvement in the Positive and Negative Syndrome Scale (PANSS) total (p < 0.0001), PANSS positive (p < 0.0001), negative (p = 0.0055) and general subscale scores (p < 0.0001). Significant improvements occurred in all PANSS scores by week 4, the first post-baseline psychopathology rating. Altogether, 50.0% of patients showed ≥20% reduction in PANSS total score, 20.6% had ≥30% reduction and 14.7% had >40% reduction. Eighteen patients (47.4%) were discharged before week 12. However, all patients experienced ≥1 adverse event. Two of 38 patients (5.2%) dropped out due to moderate leucopenia and one of them developed agranulocytosis after stopping clozapine. However, both patients recovered. Eight adverse events (hypersalivation, fatigue, sedation, constipation, insomnia, nausea/vomiting, chest pain and leucopenia) were observed in 34-79% of patients. These findings suggest that clozapine is beneficial in Japanese treatment-resistant schizophrenia patients. However, attention should be paid to patients' adverse events.
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