Performance-Modifying Influences in Dry Powder Inhalation Systems

Although dry powder inhaler (DpI) systems offer many advantages over conventional pressurized metered dose aerosols for therapeutic use, there are a number of formulation-related aspects of functionality which can significantly reduce DPI performance. A general introduction is provided to the physical requirements for preparation of efficient and effective therapeutic aerosols and dry powder inhaler systems in particular_ Of a number of important DPI design factors highlighted in the introduction, the present study concentrates on two specific ex vivo performance-modifying influences of particle characteristics used in dry powder inhalers_ Firstly, powder entrainment characteristics were studied using a model system and it was found that particle-entrainment tube (device) interactions were of two main types, depending on whether coarse or fine lactose particles were involved. In the case of coarse particles (in the range 90-180 ,..,m), entrainment was found to depend on mean linear air velocity (in the range 5-15 ms -\) and tube diameter. For fine particles (in the range 63-90 11m), entrainment was found to be dependent on both tube diameter and pressure drop at the site of entrainment. Further, in the case of lactose carrier particles> 90 11m, entrainment was found to be complete in a small velocity spread, unlike the behavior of finer particles « 90 ,..,m). Secondly, powder blend homogeneity/stability was found to be a function of the number and nature of the contacting surfaces. Optimum homogeneity of lactose / salbutamol blends was achieved with single contact surface blending. Blends were destabilized by contact with dissimilar second contact surfaces