Adhesion of Powders for Inhalation: An Evaluation of Drug Detachment from Surfaces Following Deposition from Aerosol Streams

Purpose. To evaluate micronized powder retention and detachment from inhaler surfaces following reproducible deposition by impaction, coupled with centrifugal particle detachment (CPD). Methods. Micronized albuterol sulfate (AS) and beclomethasone dipropionate (BDP) were aerosolized as dry powders and deposited by cascade impaction onto different contact surfaces. Drug detachment from the surfaces was characterized using CPD, coupled with HPLC assay and scanning electron microscopy. Results. Drugs which accumulated as aggregates on model surfaces detached with distinctive profiles for % remaining vs. applied centrifugal force; each profile showed reproducible values for the minimum force required to initiate drug detachment, F_yield. While differences occurred in the observed detachment profiles for different drugs and contact surfaces (polyacetal vs. aluminum), the deposited drug particle size had the most significant effect on these profiles, e.g., F_yield for AS (2.1-3.3 m) was 383 12.7 N compared with 18 13.8 N for AS (4.7-5.8 m). Conclusions. A technique was developed which enabled the experimental review, and subsequent data analysis, of the adhesive properties between different DPI construction materials and drug substances deposited from aerosol clouds. The technique appears to be of greater relevance to inhaler design decisions than earlier studies in the literature claiming to show differences in the adhesion of single drug particles to surfaces.