A systematic review 1 including 7 studies with a total of 419 subjects was abstracted in DARE. In 2 trials (n=120) clozapine was associated with an improvement in the Clinical Global Impression Severity Scale (CGI-S) (weighted mean difference [WMD] -1.1, 95% CI -1.24 to -0.97) and Unified Parkinson's Disease Rating Scale (UPDRS) total and motor score ( (WMD -2.39, 95% CI -3.58 to -1.20 and WMD -1.74, 95% CI -2.57 to -0.92, respectively) compared with placebo. Both studies reported an improvement in psychotic symptoms with clozapine compared with placebo. There was no difference between clozapine and placebo in early withdrawals. In one trial comparing clozapine with quetiapine (40 completed patients) there were no differences between clozapine and quetiapine for clinical efficacy, motor functioning or adverse events. In 2 trials (n=89) with quetiapine and placebo there were no differences in efficacy, safety or early withdrawals. In 2 trials (n=170) with olanzapine and placebo, olanzapine had an increased risk of early withdrawal due to adverse events (RR 7.18, 95% CI 1.76 to 29.24) and worsening of Parkinson's symptoms (UPDRS, SMD 0.59, 95% CI 0.40 to 0.78).
Comment: The quality of evidence is downgraded by study quality (inadequate allocation concealment) and imprecise results (part of studies small)
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