Selective exclusion of treatment arms in multi-arm randomized clinical trials

In this paper we discuss a design for multi-arm randomized clinical trials (RCTs) in which clinicians and their patients can selectively exclude one of the randomized treatment arms. This approach has the advantage that it should expedite protocol development, and allow easier and faster recruitment of patients into the trial. However, to preserve the randomized nature of treatment comparisons, not all recruited patients can be included in all treatment comparisons. This dictates that treatment arms are compared in a pairwise fashion, and that the numbers of patients included in different treatment comparisons may not be equal. The total trial size of a multi-arm RCT that allowed selective exclusion of arms would be greater than the size of an equivalent standard multi-arm RCT. However, the duration of time taken to recruit the study would be reduced. The implications for the design, monitoring and analysis of such RCTs are discussed.