Sometimes, it is not possible to demonstrate superiority but may be sufficient to demonstrate efficacy and safety equivalence, particularly if the marketing strategy is based on price.
Equivalence trials usually require very large sample sizes due to small efficacy differences between the two treatments. Equivalence trials typically do not include a placebo group; therefore, both treatments should have previously demonstrated superior efficacy to placebo, which may be difficult to achieve when the standard-of-care drug has not been stringently evaluated for efficacy and is used to treat a condition for which it is not approved (Makuch 1989). In addition, equivalence trials require the trialist to choose a clinically relevant treatment difference to determine the appropriate sample size, which is often difficult to do (Makuch 1986).
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