A review of current practice in the design and assessment of internal pilots in UK NIHR clinical trials

BACKGROUND: Internal pilots provide useful information which can help to optimise the running of the main trial. Although some recommendations exist in the literature for the design of internal pilots, little is known about current practice in terms of the specification and also the assessment of progression criteria. The aim of the review is to provide an overview of current practice. METHODS: A cohort of clinical trials with an internal pilot, funded by the National Institute for Health Research (NIHR), Health Technology Assessment programme (HTA), extracted in 2017 was reviewed. Data were extracted from: project descriptions; summary of changes from the first stage; feedback about the full application; monitoring notes; progress report history and protocols, for information about the design and assessment of internal pilots. RESULTS: Fifty-seven studies were reviewed. An internal pilot was first proposed in the early stages of the trial in the majority of cases. Target number for recruitment, rate of randomisation, retention/primary outcome ascertainment rate, rate of treatment adherence and consent rate were included as progression criteria. All but one study was permitted to continue to the main trial; however, 25% did not strictly meet the progression criteria. Changes were made to the design of the main trial for 25% of studies, mainly in terms of conduct of recruitment. CONCLUSIONS: This review provides insight into the process of designing and assessing internal pilots. Progression criteria are sometimes not met; however, committees involved in the reviewing process will recommend continuation to the main trial, usually accompanied by a second review or close monitoring. Recommendations are made to optimise the process. ELECTRONIC SUPPLEMENTARY MATERIAL: The online version of this article (10.1186/s13063-019-3669-9) contains supplementary material, which is available to authorized users.