Efficacy of olanzapine and ziprasidone for the treatment of schizophrenia: a systematic review.

It is difficult to determine the relative efficacy of atypical antipsychotics for the treatment of schizophrenia, based on the available literature. The purpose of this article is to review and compare the efficacy of two atypical antipsychotics: olanzapine and ziprasidone.This review focused on randomised trials in which these two antipsychotics were compared with placebo, conventional antipsychotics and each other. Common efficacy measures were the Brief Psychiatric Rating Scale, Positive and Negative Syndrome Scale and Schedule for Assessment of Negative Symptoms. When sufficient data were available, the mean treatment effect (with 95% confidence intervals) was computed and presented. Olanzapine was consistently found to be significantly superior to placebo and comparable with, or superior to, haloperidol for the treatment of overall, positive and negative schizophrenic symptoms. Ziprasidone appears to have significantly greater efficacy than placebo for overall and negative symptoms, but it remains uncertain whether ziprasidone is comparable in efficacy with conventional antipsychotics such as haloperidol. Two unpublished clinical trials have directly compared olanzapine and ziprasidone. One of these trials found no significant efficacy differences between the two drugs, whereas the results of the other study favoured olanzapine. Compared with ziprasidone, olanzapine has a larger body of evidence supporting its efficacy, and a greater proportion of findings for olanzapine have been published, allowing for greater scrutiny of results. Both drugs appear to be superior to placebo for the treatment of overall and negative symptoms of schizophrenia, but olanzapine generally compares more favourably with conventional antipsychotics. Firm conclusions regarding the comparison between olanzapine and ziprasidone require additional published trials on ziprasidone, particularly in direct comparison with olanzapine.