Efficacy of olanzapine in comparison with clozapine for treatment-resistant schizophrenia: evidence from a systematic review and meta-analyses

Introduction. Clozapine is considered the gold standard for the treatment of patients with treatment-resistant schizophrenia (TRS); however, randomized controlled trials (RCT) of olanzapine showed efficacy similar to clozapine in patients with TRS. Methods. A systematic review was conducted comparing clozapine with olanzapine in patients with TRS. Meta-analyses were performed for single outcome measures. Response to treatment was measured by the percentage of responders, or mean change or endpoint values of psychotic symptoms scales. Effect sizes were shown as relative risks (RR), or standardized mean differences, with 95% confidence intervals. Findings. Seven RCT were included, comprising 648 patients. Five meta-analyses were performed. Olanzapine and clozapine had similar effects on dropout rates (RR=0.93, CI95% = 0.77-1.12), PANSS total endpoints (SMD=0.21, CI95% = -0.04-0.46), and PANSS total mean changes (SMD=0.08, CI95% = -0.01-0.027). Clozapine was superior to olanzapine for PANSS positive (SMD=0.51, CI95% = 0.17-0.86) and negative (SMD=0.50, CI95% = 0.16-0.85) subscales. There was a trend toward high doses of olanzapine producing higher effect sizes for this drug. Conclusions. The results of this study suggest that clozapine is significantly more efficacious than olanzapine in improving positive and negative symptoms in TRS patients.