Evaluation of an Abbreviated Impactor for Fine Particle Fraction (FPF) Determination of Metered Dose Inhalers (MDI)

Abbreviated impactors have been developed recently to allow more rapid evaluation of inhalation products as alternates to the eight-stage Andersen Cascade Impactor (ACI) which has been widely used in the pharmaceutical industry for assessing aerodynamic particle size distribution. In this paper, a two-stage abbreviated impactor, Westech Fine Particle Dose Impactor (WFPD), was used to characterize the aerodynamic particle size of metered dose inhaler (MDI) products, and the results were compared with those obtained using the standard eight-stage ACI. Seven commercial MDI products, with different propellants (chlorofluorocarbon/hydrofluoroalkane) and formulation types (suspension/solution, dry/normal/wet), were tested in this study by both WFPD and ACI. Substantially equivalent measures of fine particle fraction were obtained for most of the tested MDI products, but larger coarse particle fraction and extra-fine particle fraction values were measured from WFPD relative to those measured using the ACI. Use of the WFPD also produced more wall loss than the ACI. Therefore, it is recommended that the system suitability be evaluated on a product-by-product basis to establish substantial equivalency before implementing an abbreviated impactor measurement methodology for routine use in inhaler product characterization.