A comparison of dry powder inhaler dose delivery characteristics using a power criterion

A novel method is described that compares the in vitro drug delivery characteristics of different dry powder inhalers (DPIs) based on the power supplied by the air flow. Power is defined as the rate at which work is done by the air flow and is equal to the product of pressure gradient and air flow rate through the inhaler. Tests were conducted to compare the emitted dose and fine particle fraction of the total dose (FPFTD) of the Diskus, Diskhaler, and a proprietary powder dispersion device (PDD) containing fluticasone propionate/lactose powder blends. Three power levels were selected: 1, 2, and 3 W, representing a range of inspiratory efforts. The Diskus and PDD were independent of power, delivering consistent doses and fine particle fractions over the range of powers evaluated. Diskhaler was dependent on power, the emitted dose and FPFTD significantly decreasing at the lower power level (1W) (p < 0.005). Diskus and Diskhaler are trademarks of the Glaxo Wellcome group of companies.