PERFORMANCE-MODIFYING INFLUENCES IN DRY POWDER INHALATION SYSTEMS

Although dry powder inhaler (DPI) systems offer many advantages over c onventional pressurized metered dose aerosols for therapeutic use, the re are a number of formulation-related aspects of functionality which can significantly reduce DPI performance. A general introduction is pr ovided to the physical requirements for preparation of efficient and e ffective therapeutic aerosols and dry powder inhaler systems in partic ular. Of a number of important DPI design factors highlighted in the i ntroduction, the present study concentrates on two specific ex vivo pe rformance-modifying influences of particle characteristics used in dry powder inhalers. Firstly, powder entrainment characteristics were stu died using a model system and it was found that particle-entrainment t ube (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 mu m), entrainment was found to depend on mean linear air velocity (in the range 5-15 ms(-1)) and tube diame ter. For fine particles (in the range 63-90 mu m), entrainment was fou nd to be dependent on both tube diameter and pressure drop at the site of entrainment. Further, in the case of lactose carrier particles > 9 0 mu m, entrainment was found to be complete in a small velocity sprea d, unlike the behavior of finer particles (< 90 mu m). Secondly, powde r 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 sur faces.