Characterization of nifedipine microparticles prepared by hot air coating technique.

In the present work, the Hot Air Coating (HAC) technique was used to prepare microparticulate systems containing nifedipine. Binary mixtures constituting of nifedipine and cetearyl alcohol (CA) in different proportions (30:70, 50:50, 70:30) were studied: they were homogenized by mixing or milling before spray treatment and successively subjected to a coating procedure with the HAC apparatus fed with air at 120°C under a pressure of 4.5 atm. Morphology, entrapment efficiency, drug stability, thermal behaviour and the drug dissolution profile of HAC-treated and non-treated materials were examined and compared. The HAC products show the possession of physical and physico-chemical properties and dissolution behaviour different from those of the initial physical mixtures. The operative conditions employed in the spray process allow the obtaining of microparticles containing relevant percentages of the drug (at least up to 50%). Moreover, the experimental results give evidence that the milling pre-treatment of mixtures, unlike mixing, has significant effects on the properties of the lipid-coated microparticles.