A comparison of the performance of two modern multidose dry powder asthma inhalers

Little is known about the shot potency and dose consistency of many of the inhalers in common use, and until recently there has been little consensus over the best way to evaluate these parameters. Since marked effects can be achieved with the inhaled route, more information is needed about the dosing characteristics of all available inhalers. As there are now two multidose powder inhalers available in the U.K. capable of supplying 1 month or more of treatment, this study was designed to compare the delivery characteristics of these two dry powder inhalers delivering glucocorticosteroids. The method used was in vitro analysis of the emitted dose and fine particle fraction throughout the life of five of each type of device. The multidose powder inhaler delivered between 87 and 93% of the label claim dosage, whilst the reservoir device delivered 40-58%. There was no fall off of shot potency towards the end of either device's life. Fine particle fraction for the multidose and reservoir systems, was 21 and 18%, respectively, at 60 l min-1 flow, but fell to 16 and 6% at 28.3 l min-1. In conclusion, there were statistically significant differences (P < 0.0001) in the drug emission of both dose and fine particle fraction of these two powder inhalers.