Using AFM to investigate how fines improve DPI performance

The inclusion of fine excipient particles in carrier-based dry powder inhalations is now a well characterised technique for improving formulation performance. This work applies the recently developed cohesive-adhesive balance approach to adhesive force measurement by AFM to the study of this area. The relative adhesion between four drugs and four fine excipients was measured and compared to the in-vitro deposition of drug and fine excipient from lactose carrier-based formulations. The results suggested that when the drug is more adhesive to the fines than cohesive, increased drug adhesion to the fine excipient produces improved formulation performance, possibly via the formation of agglomerates. When the drug is more cohesive than adhesive to the fine excipient however, formulation performance is not affected by drug-fines interparticulate interactions.