In Vitro Testing of Dry Powder Inhalers

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Abstract
There is increasing focus on the development of dry powder inhalers (DPIs) for the delivery of therapeutic entities to the lungs. In vitro testing of metered-dose inhalers (MDIs) has evolved through the years and general tests and methods have been published through USP general chapter , monographs, and guidelines issued by the FDA. In contrast, very few guidelines have been established for the testing of dry powder inhaler systems. In fact, these systems may prove to be more difficult to propose general tests for because they are based on different principles leading to a greater diversity in the number of types of devices and formulations in comparison to the MDIs. To form absolute standards at this stage will be difficult and this paper will present a comparison of the in vitro test methods of MDIs to some of the DPIs that are commercially available and suggests some guidelines to follow.