Placebo-Controlled, Antidepressant Clinical Trials Cannot Be Shortened to Less Than 4 Weeks’ Duration

Abstract

In double-blind, randomized, placebo-controlled clinical trials for major depressive disorder (MDD), the impact of study duration on outcome has not been adequately studied. Our aim was to examine whether placebo-controlled antidepressant trials in MDD could be shortened to less than 4 weeks. In order to accomplish this, we examined the relationship between a "positive" or "negative" finding early on (weeks 1-4), and outcome at end point. MEDLINE/PubMed publication databases were searched for randomized, double-blind, placebo-controlled trials of antidepressants for adults with MDD published between January 1, 1980, and July 1, 2009 (inclusive). One hundred seventy-five articles were found eligible. We obtained required measures during the required time points for 101 articles (57.7%). Final inclusion of articles was determined by consensus among the authors. One hundred eighty-two drug-placebo comparisons from 104 clinical trials were pooled (29,213 patients). The strength of the relationship between early and end point outcome increased progressively. However, only at week 4 did the diagnostic odds ratio (27.44) indicate strong concordance between early and end point outcome. The specificity of early outcome as a predictor of end point outcome did not vary substantially from visit to visit (0.91-0.92), while the sensitivity increased proportionally with each visit (from 0.17 to 0.72). The present analysis suggests that antidepressant clinical trials cannot be shortened to less than 4 weeks' duration, primarily due to the increased risk of erroneously concluding that an effective treatment is ineffective. Four weeks is the minimum adequate length of a trial in order to reliably detect drug versus placebo differences.