FDA and CPMP rulings on subgroup analyses

The extent to which subgroup analyses should affect the interpretation and conclusions in a trial report is a contentious matter, and guidelines regarding this issue have been established by the US Food and Drug Administration (FDA) and the EU Committee for Proprietary Medicinal Products (CPMP). Subgroup analyses should be set out in the protocol of clinical trials. The treatment effect itself may vary within a subgroup or covariate. In some cases, interactions are anticipated or are of particular a priori interest; hence a subgroup analysis or a statistical model including interactions is part of the planned analysis. However, subgroup or interaction analyses are often merely exploratory and should be clearly identified as such in the protocol. When exploratory, these analyses should be interpreted cautiously. Market approval of a compound is based on the overall trial results, and, importantly, no drug has so far been approved or not-approved either in the US or in the EU on the basis of subgroup analysis. However, subgroup analysis can influence the approval or can even be required, and therefore it can influence the labelling of the Summary Characteristics of a Product. Two examples in heart failure are given by the Val-HeFT trial comparing valsartan to placebo and the MERIT-HF trial comparing metoprolol to placebo, from which some remarkable regulatory issues arose that were debated by the FDA and CPMP.