Internal pilot
TSC, VTE
RECRUITMENT, STAGGERED
There will be an internal pilot of feasibility at the end of 6 months of recruitment (beginning of month 7 to end of month 12 of the overall study timeline). We will start recruiting the (minimum) 50 sites at four sites per month. The 100% recruitment rate to meet the sample size is 20 participants per centre month (accounting for the staggered site set-up). This equates to a target of 1440 participants at the end of the 6-month internal pilot. A stringent criterion of <5% failure to receive allocated intervention is set as a marker of crossover between trial arms. Regarding follow-up, a marker of <15% lost to follow-up would be indicative of green progression. The amber criteria is set at 75%–99% of recruitment. This equates to a minimum of 1080 participants across the 6-month internal pilot period and an associated mean recruitment rate of 15 participants per centre month. We have set an amber criterion for site set-up independent of total recruitment number, hence, even if the total participant number is at 100%, if the number of sites set-up is <24 then this would stimulate a review of the site set-up strategy. Any amber criteria would prompt a review of the trial methodology and recruitment strategy. The red criteria, that is, consideration of stopping the trial early, is set at <75% recruitment and is equivalent to achieving fewer than 1080 participants across the 6-month internal pilot period. An independent threshold for site set-up has been set at <18 sites. The TSC will meet at the end of month 13 (allowing 1 month of processing time after the 6 months of recruitment) with blinded estimation of the rate of VTE for each arm. This will confirm the sample size or lead to a sample size re-estimation.