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.