Recruitment across two decades of NIH-funded Alzheimer's disease clinical trials

BackgroundTimely accrual of a representative sample is a key factor in whether Alzheimer's disease (AD) clinical trials successfully answer the scientific questions under study. Studies in other fields have observed that, over time, recruitment to trials has become increasingly reliant on larger numbers of sites, with declines in the average per-site recruitment rate. Here, we examined the trends in recruitment over a 20-year period of NIH-funded AD clinical trials conducted by the Alzheimer's Disease Cooperative Study (ADCS), a temporally consistent network of sites devoted to interventional research.MethodsWe performed retrospective analyses of eleven ADCS randomized clinical trials. To examine the recruitment planning, we calculated the expected number of participants to be enrolled per site for each trial. To examine the actual trial recruitment rates, we quantified the number of participants enrolled per site per month.ResultsNo effects of time were observed on recruitment planning or overall recruitment rates across trials. No trial achieved an overall recruitment rate greater than one subject per site per month. We observed the fastest recruitment rates in trials with no competition and the slowest in trials that overlapped in time. The highest recruitment rates were consistently seen early within trials and declined over the course of studies.ConclusionsTrial recruitment projections should plan for fewer than one participant randomized per site per month and consider the number of other AD trials being conducted concurrently.

Automated summary

This study analyzed the recruitment trends of 11 Alzheimer's disease clinical trials conducted over a 20-year period. The study found that there were no significant changes in recruitment planning or overall recruitment rates over time. None of the trials achieved a recruitment rate of more than one participant per site per month. Trials with no competition had the fastest recruitment rates, while trials that overlapped in time had the slowest rates. The study suggests that recruitment projections should plan for less than one participant per site per month and consider the number of other trials being conducted concurrently.