Theophylline-loaded microparticles of a lipid carrier, PrecirolR ATO 5, were prepared by the ultrasonic spray-congealing method. The goal of the work was to investigate the effect of different concentrate ions and kind of colloidal silicon dioxide (AerosilR 90, 200 and 300) on the microparticle characteristics (particle size, drug loading, morphology and kinetics of release). The results showed that the introduction of AerosilR improved the drug distribution in the different particle sizes and that the mean diameter of the microparticles decreased with the viscosity of the suspension to be nebulized, especially that with AerosilR 300. Whatever the microparticles formulation is, SEM and image analysis did not reveal any remarkable difference of the microparticle shape and surface area, suggesting that other parameters could influence the dissolution behaviour.
