An investigation into the mechanism of dissolution rate enhancement of poorly water-soluble drugs from spray chilled gelucire 50/13 microspheres

The production and physicochemical characterisation of spray chilled Gelucire 50/13 microspheres is described with a view to improving the dissolution of a poorly water-soluble drug, piroxicam, and understanding the fundamental mechanisms associated with the improved drug release. Thermorheological testing was developed as a fast screening method for predicting the processability of dispersions for spray chilling preparation. Spray chilled piroxicam loaded microspheres were spherical in shape with a median diameter of circa 150 µm. DSC indicated no interaction between piroxicam and lipid matrix, while HSM studies performed in polarized light mode indicated that the spheres contained distinct drug crystals. Polarising light microscopy and small-angle XRD investigations on the hydration behaviour of the lipid and the spray chilled microspheres revealed the formation of liquid crystalline phases depending on the degree of hydration. The dissolution behaviour of the piroxicam loaded microspheres showed significant improvements compared to drug alone. The particle size, drug loading and aging of the microspheres were all found to have an influence on the release behaviour. It was proposed that Gelucire 50/13 microspheres release the entrapped piroxicam via formation of a lyotropic liquid crystalline phase, which allows dissolution of the drug particles in a finely divided, high surface area and well-wetted state. © 2009 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 99:262-274, 2010