Attrition and discontinuation in amyotrophic lateral sclerosis clinical trials: a meta-analysis

Objectives: Attrition due to adverse events and disease progression impacts the integrity and generalizability of clinical trials. The aim of this study is to provide evidence-based estimates of attrition for clinical trials in amyotrophic lateral sclerosis (ALS), and identify study-related predictors, through a comprehensive systematic review and meta-analysis. Methods: We systematically reviewed the literature to identify all randomized, placebo-controlled clinical trials in ALS and determined the number of patients who discontinued the study per randomized arm. Subsequently, we meta-analyzed attrition rates across studies, evaluated the difference between study arms, and explored the impact of study-level characteristics. Finally, a meta-regression model predicting study discontinuation for future clinical trials was translated into a web application. Results: In total, 60 randomized placebo-controlled clinical trials were included in the meta-analysis, randomizing 14,493 patients with ALS. Attrition varied significantly between studies, ranging from 3.1% to 75.7% of all randomized patients, with a pooled effect of 32.0% (90% prediction interval 6.1% to 66.3%). Attrition was similar between the intervention and placebo arm (odds ratio 1.08, 95% CI 0.89 to 1.31, p = 0.43). The follow-up duration was identified as the sole study-level predictor (0.032, 95% CI 0.026 to 0.039, p < 0.001), resulting in predicted attrition of 19.3% for 6-month, 36.4% for 12-month, and 55.6% for 18-month clinical trials. Conclusions: ALS clinical trials encounter high attrition, which increases with the follow-up duration. These findings underscore the need to refine our strategies to manage attrition, preserving the integrity and generalizability of ALS clinical trials.