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Superiority and equivalence in thrombolytic drugs: an interpretation.

Streptokinase and alteplase both reduce mortality from acute myocardial infarction. Newer thrombolytic drugs (reteplase and tenecteplase) have putative advantages, such as ease of delivery and better fibrin specificity, although they are more expensive. A systematic review and meta‐analysis identified the clinical efficacy and adverse effects of these drugs.1 But this can only compare drugs where there are direct trial comparisons. Inevitably, we need to make indirect comparisons also, as well as to interpret the results of the direct comparisons. We present an interpretation and consider its strengths and weaknesses.

Broadly, ‘superiority studies’, where one drug is thought likely to be better than another, assume a null hypothesis that there is no difference, which may then be disproved. Such studies are usually analysed by intention to treat (ITT, i.e. to analyse all patients according to their initial randomized allocation, and not whether they ever received the therapy or changed at some point to the alternative therapy). The null hypothesis and ITT are conservative, and limit the chances of a type 1 error, i.e. ascribing a difference where none exists.2

Equivalence trials examine whether a new therapy is as effective as an existing standard. Equivalence studies might also be used to compare adverse effects, or costs of two effective drugs. In a randomized trial, the two drugs are unlikely to produce exactly the same results (this would be the case even if we compared one drug to itself). We must therefore define ‘equivalence’ a priori , i.e. what is the range of apparent difference in efficacy between two therapies, within which the therapies may be considered clinically equivalent. This is an arbitrary decision.

For thrombolytics, the efficacy is usually recorded as 30‐ or 35‐day mortality. The American College of Chest Physicians (ACCP)3 and others4 have suggested that the …