Explanation

In a randomised trial, a key goal is to have comparable study groups that differ only by the intervention being evaluated. Bias can arise when the trial groups receive different concomitant care, e.g., additional interventions that may impact trial outcomes.(247)

Trials may differ in what is meant by the “intervention being evaluated”. In some trials (with a marked explanatory approach), the “intervention” may be defined narrowly as the experimental intervention tested. In other trials (with a more pragmatic approach), the “intervention being evaluated” may be defined as the experimental intervention plus allowed concomitant interventions and procedures, e.g., rescue interventions. Also, in some multicentre trials, an intervention is added to “usual care”, which may differ considerably in content between centres (Item 15a).

Reviews of two samples of 108 and 292 trial protocols from 2016 found that 69% and 81% respectively reported the concomitant care that was permitted.(9, 10)

The protocol should list the relevant concomitant care that is allowed (including rescue interventions) and prohibited during the conduct of the trial. “Relevant” concomitant care refers to concomitant care and interventions that could affect the trial outcome. Plans for recording any allowed and prohibited concomitant care during the trial should also be reported.

Summary of key elements to address

● Relevant concomitant care that is allowed (e.g., rescue interventions) or prohibited during the trial

● Any plans to record concomitant care received, including “usual care”