High-pressure aerosol suspensions--a novel laser diffraction particle sizing system for hydrofluoroalkane pressurised metered dose inhalers

In this study, a novel laser diffraction particle size analysis dispersion system, capable of sizing particles in situ within suspension hydrofluoroalkane (HFA) pressurised metered dose inhalers (pMDIs), was developed and tested. The technique was compared to four indirect particle sizing methods commonly used to determine the size of particles suspended in HFA pMDIs. The median volume diameter obtained using laser diffraction of both the salbutamol sulphate and fluticasone propionate suspended either in 2H, 3H-decafluoropentane or perfluoropentane (employed as surrogate propellants) was over one-order of magnitude larger than the particle sizes of the drugs suspended in HFA 134a. In contrast, the "in-flight" particle size using the Sympatec inhaler 2000 laser diffraction equipment undersized the particles, predicting higher delivery efficacy compared to the other sizing methods. However, the size of particles suspended in HFAs derived using the novel pressurised dispersion system, showed a linear correlation with the impaction results, r2=0.8894 (n=10). The novel pressure cell sizing technique proved to be simple to use, has the ability to be automated and was accurate, suggesting it could be an essential tool in the development of new suspension-based pMDI formulations.