The influence of particle size distribution and surface roughness of carrier particles on the in vitro properties of dry powder inhalations

The influence of the amount of fine carrier particles, the shape of the particle size distributions, and the surface roughness of the coarse carrier particles on the aerodynamic properties of interactive powder mixtures from Salmeterol Xinafoate and lactose monohydrate have been investigated. In a further set of experiments, the influence of preconditioning the carrier powder by blending was compared with the performance of an unconditioned powder. A higher amount of fine carrier particles in interactive mixtures was found to improve the aerodynamic properties of dry powder inhalations. Fine carrier particles may form agglomerates with the micronized drug and deposit in the air stream according to the aerodynamic properties of the agglomerates, rather than that of the single particles. However, this effect also appears to be linked to the surface roughness of the more coarse carrier particles. A smoother surface of the coarse carrier particles may lead to formation of autoadhesion layers around them, which can cause embedment of the micronized drug particles and thus hinder detachment during inhalation. The results obtained using preconditioned lactose monohydrate powders as opposed to unconditioned lactose monohydrate powders suggest that preconditioning by blending can be disadvantageous or of no importance in terms of the aerodynamic behavior of dry powder inhalations for some lactose monohydrate batches, while it improves these properties for others. The surface roughness of the coarse carrier particles influences the effect that preconditioning has on the performance of dry powder inhalations. The data suggest that carrier materials with relatively smooth surfaces are indifferent to preconditioning in terms of the aerodynamic properties of the dry powder inhalations, whereas carrier powders with comparatively rough surfaces lose their ability to function as carrier particles for a micronized drug in a dry powder inhalation. The results indicate that a rugosity of the carrier particles of about 1.3 mu m is optimal in terms of the function of a dry powder inhalation if preconditioning is sought.