Calculating Particle Size Distribution Metrics for Inhaled Product Characterization
Cascade impaction is mandatory for the measurement of aerodynamic particle size in all orally inhaled and nasal drug products (OINDPs). It provides information that is crucial when assessing the likely deposition behavior of the drug during inhalation and is used as an in vitro indicator of delivery efficiency. There is widespread interest in and considerable discussion about the best approach to streamlining analysis of the data that multistage cascade impaction generates. Beginning with an introduction to the technique, the authors discuss the analysis of the resulting data, focusing on methods for the calculation of mass median aerodynamic diameter, one of the metrics routinely used for comparative testing. It concludes with a review of current industry thinking as to the most appropriate way to characterize OINDP particle size.