Evaluation of Different Powder Characterization Techniques for DPI Performance in Capsule-based Inhalers
Salvatore Pillitteri1, Joana T. Pinto2, Sarah Zellnitz-Neugebauer2, Aurélien Neveu1 & Filip Francqui1
1Granutools, Rue Jean Lambert Defrêne 107, Awans, 4340, Belgium
2Research Center Pharmaceutical Engineering GmbH, Inffeldgasse 13, 8010 Graz, Austria
We investigated the rheological properties of dry powder inhaler (DPI) formulations, composed of an adhesive mixture of salbutamol sulphate and different lactose grades, with tapped density and rotating drum methods. The results from these characterization methods were compared to the performance of the DPI, evaluated by the fine particle mass (FPM) released after aerosolization from a capsule-based inhaler. We found that the dynamical measurement provided by the rotating cell could be more relevant to understand inhaler performance than quasi-static ones. On the one hand, we observed that the classification that can be done with a quasi-static measurement, i.e., with the tapped density measurement and the rotating drum at low speed, is completely different from the classification proposed by a dynamical measurement, performed with the drum at high rotating speed. This difference is due to rheological properties of the powders, such as shear-thinning and shear-thickening behaviours. On the other hand, the flow state undergone by the powder during aerosolization is dynamical in a capsule-based inhaler since the powder is released by a pierced capsule that rotates to a speed up to 1000 rpm. These results highlight the relevance of dynamics measurement for DPI performance characterization and optimization.
The aeration and the Dynamic Cohesive Index measured at high rotating speed seem useful indicators to characterize the performance of DPI. Indeed, the shear-thinning or the shear-thickening behaviour observed in some powders completely inverse the classification that could be made with static or quasi-static measurements.