Spray-drying enteric polymers from aqueous solutions: a novel, economic, and environmentally friendly approach to produce pH-responsive microparticles.

We describe a novel method to fabricate pH-responsive microparticles suitable for oral delivery using an aqueous-based spray-drying approach. The approach involves the neutralization and generation of water-soluble salt forms of enteric polymers. The methacrylic acid polymers (Eudragit L and Eudragit S) were added separately to aqueous solutions of ammonium hydrogen carbonate; the solutions were then spray-dried. FTIR analysis of the harvested microparticle products identified the presence of ammonium methacrylate with the appearance of a peak at 1550 cm(-1) corresponding to the stretching of the N-H bond. Incubating the microparticles for three hours at 70°C and 130°C for the Eudragit S and L products, respectively, was sufficient to eradicate the ammonium residues. The microparticles, loaded with the model drug prednisolone, were spherical and small in size (2-5 μm). Moreover, the particles were gastro-resistant, and release was rapid and complete at small intestinal conditions. The pH threshold of release of the Eudragit S and Eudragit L microparticles was lowered from 7 and 6 to 6.5 and 5.5, respectively. In bicarbonate media, which are physiological and representative of the conditions of the proximal small intestine (mHanks) and the distal small intestine (Kreb's), drug release from these spray-dried microparticles was faster compared to microparticles produced from conventional emulsion solvent evaporation methods. This new microparticle preparation concept obviates the need for organic solvents and utilizes spray-drying techniques that are amenable to industrial application; the approach therefore offers economic, safety, and environmental benefits.