Impact of patient selection and study characteristics on signal detection in placebo-controlled trials with antidepressants

An increasing rate of antidepressant trials fail due to large placebo responses. This analysis aimed to identify variables influencing signal detection in clinical trials of major depressive disorder. Patient-level data of randomized patients with a duloxetine dose ≥60 mg/day were obtained from Lilly. Total scores of the Hamilton Depression Rating scale (HAM-D) were used as efficacy endpoints. In total, 4661 patients from 14 studies were included in the analysis. The overall effect size (ES), based on the HAM-D total score at endpoint, between duloxetine and placebo was −0.272. Although no statistically significant interactions were found, the following results for factors influencing ES were seen: a very low ES (−0.157) in patients in the lowest baseline HAM-D category and in patients recruited in the last category of the recruitment period (−0.122). A higher ES in patients recruited in centers with a site-size at but not more than 2.5 times the average site-size for the study (−0.345). Study characteristics that resulted in low signal detection in our database were: <80% study completers, a HAM-D placebo response >5 points, a high variability of placebo response (SD > 7 points HAM-D), >6 post baseline visits per study, and use of an active control drug. Simpler trial designs, more homogeneous and mid-sized study sites, a primary analysis based on a higher cutoff blinded to investigators to avoid the influence of score inflation in mild patients and, if possible, studies without an active control group could lead to a better signal detection of antidepressive efficacy.