Microencapsulation of drugs with aqueous colloidal polymer dispersions

Sustained-release polymer particles containing drugs with various solubility characteristics (ibuprofen, theophylline, guaifenesin, and pseudoephedrine HCl) were prepared with colloidal polymer dispersions in a completely aqueous environment as an alternative to conventional microencapsulation techniques, which use organic solvents. Spherical particles were prepared by spraying or dropping dilute sodium alginate solutions (0.67%, w/w) containing the dissolved or dispersed drug and colloidal polymer particles into calcium chloride solutions. The gelled particles, which formed by ionotropic gelation of the polysaccharide with calcium ions, were dried and cured at 60 degrees C to cause fusion of the colloidal polymer particles into a homogeneous matrix system. Actual drug contents close to 50% and encapsulation efficiencies of between 80 and 98% were achieved with all drugs. Guaifenesin and ibuprofen acted as plasticizers for the ethyl cellulose pseudolatex, whereas with theophylline and pseudoephedrine HCl, dibutyl sebacate had to be added as a plasticizer to yield a nondisintegrating polymer matrix. The stirring time before separation of the particles from the gelation medium had to be minimized with the water-soluble drugs to maximize drug loading; however, it was not critical with the water-insoluble drugs. Drug release was a function of the solubility of the drug, drug loading, and the type of polymer dispersion used.