Early Onset of Antipsychotic Action in Schizophrenia: Evaluating the Possibility of Shorter Acute Efficacy Trials

Extended placebo-controlled clinical trials in schizophrenia research pose an ethical challenge. This study examines factors that have implications for the design and duration of placebo-controlled acute efficacy trials: Does early response discriminate active drug (AD) from placebo, and are the early differences sustained over time? A post hoc pooled analysis of 2 randomized 6-week double-blind clinical trials was performed comparing patients with schizophrenia treated with placebo or low-dose olanzapine (1 mg/d; placebo/low dose [PBO] group, n = 170) to patients treated with a 10- to 20-mg/d dose of haloperidol or medium- to high-dose olanzapine (7.5 to 17.5 mg/d; AD group, n = 252). Mixed-model repeated-measure analysis tested for group differences. Power analysis was undertaken to compare study designs with shorter durations. At 2 weeks, the mean reduction in the Brief Psychiatric Rating Scale total score was significantly greater for the AD group (-10.1) compared with the PBO group (-4.1; P < 0.001); this difference was sustained until the study ended (6 weeks). A higher proportion of early treatment responders were observed for the AD group (52%) compared with the PBO group (29%; P < 0.001). Early nonresponse to placebo or drug was predictive of subsequent nonresponse (negative predictive value: PBO = 95%, AD = 84%). Power analysis indicates that the placebo-drug differences are robust at 2 weeks. Treatment responders from the AD and the PBO groups followed a similar response path. Early response to antipsychotic treatment discriminated AD from placebo. Reducing placebo-controlled clinical trials from 6 weeks to 2 to 4 weeks was found to be a viable option for efficacy identification in acutely ill patients.