Patent ID: 8048451

Claim:
A method of preparing microparticles for use in a pharmaceutical composition for pulmonary administration, comprising particles of active substance having, on their surfaces, particles of a hydrophobic material suitable for delaying the dissolution of the active substance, the method comprising milling particles of the active substance, wherein particles of hydrophobic material are present during said milling, so as to ensure a sufficient break-up of agglomerates of both active and hydrophobic material, dispersal and even distribution of the hydrophobic material over the active material, so that the particles of hydrophobic material become fused to the surface of the particles of active material, said microparticles exhibiting delayed dissolution as compared to the particles of the active substance, wherein the milling is dry milling, and wherein the milling comprises: (a) passing a mixture of particles of active material and particles of hydrophobic material in a fluid, through a constriction under pressure; (b) compressing a mixture of particles of active material and particles of hydrophobic material in a gap of predetermined width; or (c) jet milling particles of active material with particles of hydrophobic material.