Letter on: Predicting the Number of Sites Needed to Deliver a Multicentre Clinical Trial Within a Limited Time Frame in the UK

Rosemary J Greenwood, Julie Pell, Paula Foscarini-Cragg, Katharine Wale, Ian Thomas, Charlotte A Bradbury*

*Corresponding author for this work

Research output: Contribution to journalArticle (Academic Journal)


When planning a multicentre clinical trial, it can be difficult to predict the time needed to open individual sites and this in turn impacts on the total number of sites needed, the budget and the time frame for a clinical trial to be delivered successfully. This is of particular importance for funding applications with a limited time frame and budget such as NIHR RfPB. It is more efficient and cost effective to open the total number of sites needed at the outset of a trial, rather than to respond later to slow site opening and recruitment. Here, we share our experience of successfully delivering a multicentre clinical trial for a rare disease within a limited time frame and budget by approximately doubling the number of sites initially predicted to be needed. We initially predicted 20 sites would be needed to deliver the clinical trial, but early on in the trial, the number of sites was more than doubled to allow successful recruitment of the target sample size within the desired time frame. Of the 48 ethically approved sites, the median time from ethical approval of a site to opening for recruitment was 182 days (95% confidence interval [143 to 245 days]) and ranged from 18 days to 613 days. In four (9%) of these sites, part of the delay was due to pharmacy sign off not being given when R&D had issued capacity and capability (C&C). Delays due to pharmacy sign off varied from 10 days, to over three months delay in two sites (94 days and 102 days). A mathematical solution to the problem of planning a study with a short recruitment window has been given to support the planning and costing of grants with fixed time constraints: Number of sites = Required sample size divided by (Number of eligible patients per site per month, times recruitment rate, times (the number of months accrual minus 6 months)). We expect these results to help others who are planning multicentre clinical trials in the UK. Ethical approval from NRES Committee South West (IRAS number 225959). EudraCT Number: 2017-001171-23
Original languageEnglish
Publication statusAccepted/In press - 1 Oct 2020


  • Multicentre Randomised Controlled Trials

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