Equivalence trials in SLE research: issues to consider

In contrast to the objective of most clinical trials, which is to demonstrate superiority of an experimental treatment over a standard or placebo, the aim of an equivalence trial is to show that two treatments are equivalent in outcome or only marginally different. This would be of interest when an experimental treatment offers advantages such as reduced toxicity, ease of administration, or cost relative to the standard. Demonstrating equivalence may also be a goal when evaluating the safety of certain drugs because similarity in the risks of an adverse event in subjects exposed and unexposed to the drug is an indication of its safety. The classical formulation of the null hypothesis of treatment equality that is used in superiority trials is not applicable to equivalence trials because absolute equivalence between treatment groups cannot be proven. The strategy in equivalence trials is to define a maximum difference between treatment groups that is clinically acceptable and then assess whether there is sufficient evidence from the trial to conclude that the true treatment difference is within this acceptable range. In this paper, we discuss issues surrounding the planning, conduct, and analysis of equivalence trials in the context of SLE, with examples from the SELENA study.