Physical properties of supercritically-processed and micronised powders for respiratory drug delivery

Comparative analysis between salmeterol xinafoate (SX) powders was carried out to define quantitatively the solid-state and surface particle properties relevant to formulation of these materials into dry powder respiratory drug delivery systems. SX powders were prepared in supercritical CO₂ using a single-step crystallization process (Solution Enhanced Dispersion by Supercritical fluids, SEDS™), the volume mean diameter and deagglomeration behaviour of pure drug compound were optimised for respiratory applications. This compound together with reference samples of starting granulated material and micronised powder were used in analytical studies which involved assessment of polymorphic purity and crystallinity (domain size and strain) using high-resolution X-ray powder diffraction, determination of powder surface energetics using inverse gas chromatography (IGC), electrostatic charge and adhesion measurements. The supercritically-processed powders showed low surface energy, low strain, higher crystallinity and higher polymorphic purity than both granulated and micronised powders and resulted in reduced agglomeration, electrostatic charge and adhesion of this powder.