An investigation into the relationship between carrier-based dry powder inhalation performance and formulation cohesive–adhesive force balances

The inclusion of different carrier materials in a dry powder inhaler (DPI) system can alter formulation performance, which might be attributable to variation in the adhesion between drug and carrier particles. The aim of this study was, therefore, to further examine the relationship between drug-carrier adhesion and performance, by comparing data relating to many different drug-carrier combinations. Four drugs and four carriers were employed, giving a total of 16 combinations. The relative magnitude of the drug-carrier adhesion for each combination was quantified using the cohesion–adhesion balance (CAB) approach to colloidal probe atomic force microscopy. The in vitro inhalation performance of the 16 formulations (1.5% w/w drug) was investigated and found to vary significantly. Plots of fine particle dose against drug-carrier CAB ratio revealed that performance was optimised when the drug-carrier CAB ratio was slightly cohesive. This trend was found to fit with those from similar previous studies, although due to the smaller number of formulations investigated previously, the full extent of this relationship had not been revealed. It was concluded, therefore, that when developing a carrier-based DPI, the selection of a drug-carrier combination with a slightly cohesive CAB ratio might result in optimal performance.