Clinical equivalence testing of inhaled bronchodilators.
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There are no standardized methods to demonstrate in-vivo bioequivalence of inhaled bronchodilators. The most practical method of showing therapeutic equivalence in vivo is by estimating their relative potencies (RP) in clinical efficacy studies. The RP of bronchodilators may be estimated by comparing either their bronchodilator or bronchoprotective properties. Bronchodilator studies are easier to perform and may better model the physiologic effect of many agents, including inhaled beta-agonists. However, it may be difficult to demonstrate steep dose-response for these outcomes, except in cumulative study designs. Bioequivalence trials may be especially challenging when involving pressurized metered-dose inhalers, as a single actuation - the lowest feasible dose to include in the evaluation, may already produce bronchodilation that is at or near the plateau of the dose-response curve. Protection against bronchoconstriction induced by a direct inhaled stimulus like methacholine or histamine affords a reliable and practical method of comparing inhaled bronchodilators and estimating their RP. Inhalational bronchoprovocation testing allows for easier repeatability and quantitation of the stimulus necessary to produce a predetermined degree of bronchoconstriction, and the degree of protection afforded by the bronchoprotection agent. RP studies using adequate methodology are necessary to compare long-acting bronchodilators and both short- and long-acting bronchodilators in patients who are also on inhaled corticosteroids.
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