Efficacy claims for new drugs without clinical trial outcome data: problems and pitfalls

The definition of efficacy of a cardiovascular treatment is frequently based on its impact on surrogate endpoints. These can be laboratory results, physical signs or images that are used in clinical trials as a substitute for clinically relevant endpoints, representing how patients feel, function or survive and that supposedly predict treatment efficacy. Similar efficacy claims can be made for different drugs, based on their similar effects on the same endpoints. This approach involves generalization from one therapeutic class to another or, within the same class, from one molecule to another, thus implying that the benefits of a non-evaluated drug will be the same as those of another that has been carefully evaluated. Such generalization is more common when dealing with two drugs from the same class that are similar in chemical composition, but is less reliable when the two drugs belong to different classes. In this article we discuss the legitimacy of efficacy and safety claims for new cardiovascular drugs without outcome data from large clinical trials, based on the similarity of effects found with similar drugs that have clinical trial outcome data.