Recruitment in randomized clinical trials: The MeMeMe experience

Recruitment is essential for the success of clinical trials. We are conducting a randomized clinical trial to test the effect of a Mediterranean dietary intervention with or without 1700 mg/day of metformin for the prevention of age-related chronic diseases, the MeMeMe trial (Trial registration number: EudraCT number: 2012-005427-32 ClinicalTrials.gov ID: NCT02960711). MeMeMe recruiting experience, highlighting strengths, limitations encountered and results is reported.

Statistical analysis focused on the reasons for withdrawal according to the recruitment method ("active" versus "passive" criterion) and the time of withdrawal. Logistic regression models were used to explore the associations between the risk of withdrawal and sex, recruitment method, randomization arm, and with markers of compliance to the intervention, such as one-year change in body weight.

Out of 2035 volunteers, 660 (32.4%) were recruited "actively" and 1375 (67.6%) "passively". Among people who dropped out of the trial after randomization, there were 19.5% for the "active" and 22.0% for the "passive" method (p = 0.28). The risk of withdrawal was significantly higher in women (OR:1.91; 95% CI:1.17-3.12; p = 0.01), in volunteers older at recruitment (OR:1.25; 95% CI:1.07-1.45; p = 0.004), and in those with a higher BMI at baseline (OR:1.23; 95% CI:1.07-1.43; p = 0.004). Volunteers who lost at least 2 kg (the median weight change) in the first year of intervention were significantly less (53%) likely to withdraw from the trial (OR:0.48; 95% CI:0.30-0.75; p = 0.001).

Our findings suggest that the "passive" recruitment method was more effective than the "active" one to advance recruitment. The benefits of "passive" recruitment hardly outweighed the drawbacks.

Trial registration number: EudraCT number: 2012-005427-32. ClinicalTrials.gov ID: NCT02960711.