Application and mechanism of inhalation profile improvement of DPI formulations by mechanofusion with magnesium stearate

In our previous paper, we reported the inhalation properties of dry powder inhaler (DPI) formulations containing Compound A and mechanofusion-processed lactose carriers. The mechanofusion process with magnesium stearate (Mg-St) on the lactose carrier enhanced the fine particle fraction (FPF) value of the Andersen cascade impactor (ACI) study. The increase of FPF seemed to be associated with the increase of the dispersibility of drug particles. The objectives of this study were (1) to evaluate the applicability of lactose carrier mechanofusion-processed with Mg-St and (2) to examine the mechanism of FPF alteration by the mechanofusion process applied on the lactose carrier with or without additive. The inhalation profiles of DPI formulations containing four different pharmaceutical compounds were evaluated with an ACI. The dispersibility of the formulations was observed by particle size distribution measurement in the air stream and the adhesive force was measured bydirect separation method. It was found that higher FPF was obtained with lactose mechanofusion-processed with Mg-St as compared to control lactose carriers for all four compounds. This suggested that mechanofusion process with Mg-St is widely applicable in DPI formulations. The homogenization of surface adhesiveness was attributed to the increased FPF of the DPI including lactose mechanofusion-processed with Mg-St, as suggested by the combination of several physicochemical characteristics. Combination of different characterization methods would be of help to clarify the whole mechanism which defines the inhalation properties of DPI formulations.