Background: The clearest advantage of new generation, atypical antipsychotics is a reduced risk of extrapyramidal side-effects (EPS), compared with conventional compounds. These findings might have been biased by the use of the high-potency antipsychotic haloperidol as a comparator in most of the trials. We aimed to establish whether the new drugs induce fewer EPS than low-potency conventional antipsychotics.
Methods: We did a meta-analysis of all randomised controlled trials in which new generation antipsychotics had been compared with low-potency (equivalent or less potent than chlorpromazine) conventional drugs. We included studies that met quality criteria A or B in the Cochrane Collaboration Handbook, and assessed quality with the Jadad scale. The primary outcome of interest was the number of patients who had at least one EPS. We used risk differences and 95% CIs as measures of effect size.
Findings: We identified 31 studies with a total of 2320 participants. Of the new generation drugs, only clozapine was associated with significantly fewer EPS (RD=-0.15, 95% CI -0.26 to -0.4, p=0.008) and higher efficacy than low-potency conventional drugs. Reduced frequency of EPS seen with olanzapine was of borderline significance (-0.15, -0.31 to -0.01, p=0.07). Only one inconclusive trial of amisulpride, quetiapine, and risperidone and no investigations of ziprasidone and sertindole were identified, but some evidence indicates that zotepine and remoxipride do not lead to fewer EPS than low-potency antipsychotics. Mean doses less than 600 mg/day of chlorpromazine or its equivalent had no higher risk of EPS than new generation drugs. As a group, new generation drugs were moderately more efficacious than low-potency antipsychotics, largely irrespective of the comparator doses used.
Interpretation: Optimum doses of low-potency conventional antipsychotics might not induce more EPS than new generation drugs. Potential advantages in efficacy of the new generation drugs should be a factor in clinical treatment decisions to use these rather than conventional drugs.