Deviation of the ratio of drugs in a two-component mixture encapsulated in cellulose phthalate microspheres.

Microspheres were formed when a solution of cellulose phthalate was extruded into 30% glacial acetic acid solution. Sulphonamides entrapped in such microspheres leached into the hardening solution because they dissolved freely in the acetic acid solution. This resulted in poor loading efficiency of the sulphonamides in the microspheres. When mixtures of sulphaguanidine and sulphathiazole in various drug ratios were microencapsulated by this method, the observed drug ratios were found to be markedly changed. This was attributed to the difference in solubility of the two sulphonamides in acid such that their extent of diffusion into the hardening solution was not similar. NSAIDS such as ibuprofen and mefenamic acid which are acidic and more hydrophobic in nature are less soluble in acetic acid. These drugs were retained better in the microspheres during the hardening process and the loading efficiency was consequently improved. In cases where mixture of the NSAIDS were encapsulated, the drug ratios showed little deviation from the theoretical values. This study shows that loading of the CAP microspheres is dependent on the solubility of the drugs in acetic acid. When more than one drug is required to be microencapsulated, the drug ratio may change if the drugs have different solubility in acetic acid.