Evolution of dry powder inhaler design, formulation, and performance.

Many companies are now prioritizing the development of dry powder inhalers (DPIs) above pressurized formulations of asthma drugs. A well-designed DPI and an appropriate powder formulation can optimize the effectiveness of inhaled drug therapy. A DPI must be able to deliver medications effectively for most patients, and an ideal inhaler would provide a dose that does not vary with inspiratory flow rate. Recent regulatory guidelines, among which the U.S. FDA draft guidance is the most stringent, demand consistent dose delivery from an inhaler throughout its life and consistency of doses from one inhaler to another. However, the properties of free micronized powders often interfere with drug handling and with drug delivery reducing dose consistency. Recent advances in formulation technology can increase lung dose and reduce its variability. While a perfect DPI may never exist, both device and formulation technology are evolving to rectify perceived deficiencies in earlier systems.