Planning and monitoring of equivalence studies.

Demonstrating therapeutic equivalence of two treatments is the goal of many clinical trials. For instance, when the toxicity of an effective standard treatment is of concern, much effort is devoted to developing new therapies that would be both as effective and less toxic. In this paper we review the special characteristics of these trials and describe sequential monitoring of equivalence studies using repeated confidence intervals. We show how sequential monitoring may be of particular value in this setting and critically discuss the choice of some important design parameters. We also provide tables for use when planning a sequential equivalence trial.