Summary
In this study we introduce a modified Fast Screening Impactor, the Refined-FSI (R-FSI), in which the fine particle dose <5 µm (FPD) is collected on a Respirgard filter (303EU Airlife). This modified method speeds up FPD determinations further compared to the ordinary FSI. With this method we have characterized two formulation batches in a multidose Dry Powder Inhaler (DPI) and two batches of a combination product pressurized Metered Dose Inhaler (pMDI), comparing with the FPD results obtained using a Next Generation Impactor (NGI) for the DPI or an Andersen Cascade Impactor (ACI) for the pMDI. For both the DPI and the pMDI, the FPD<5µm as determined by the R-FSI are in good agreement with the Cascade impactor results. The agreement depends slightly on the interpolation method used for calculating the FPD<5µm for the cascade impactors. In summary, this study demonstrates the potential of the R-FSI (or FSI or an automated FSI) as a viable alternative to pharmacopeial cascade impactors for determining FPD<5µm in DPIs and pMDIs. It also highlights the importance of interpolation method used for FPD<5µm and the potential for removing the impactor mass balance criteria by using this non-complex equipment and thereby also moving towards automated FPD determinations.