Assessing equivalence of inhaled drugs

The move to disease management has led to an increase in the practice of drug or formulation substitution on the basis of equivalence. Well established guidelines are available for judging equivalence between oral, but not inhaled, formulations. This article describes the criteria by which equivalence can be assessed and concludes that although traditional issues such as adequate sample size are important, studies also need to be designed in such a way as to avoid the possibility of falsely concluding clinical equivalence.