Effect of surface active agents on drug release from polylactic acid-hydrocortisone microcapsules

Polylactic acid microcapsules containing randomly distributed hydrocortisone particles were prepared. The rate of release of hydrocortisone from the microcapsules in pH 7.4 phosphate buffer was found to be largely increased by the presence of polysorbate 80, cetylpyridinium chloride, or aerosol OT in the dissolution medium. The surfactant effect was attributed to the ability of the surface active agent to improve solvent penetration into the microcapsules by lowering the surface tension at the solid-liquid interface. The effect of the cationic surfactant, cetylpyridinium chloride on the rate of drug release is similar in magnitude to that of the nonionic surfactant, polysorbate 80. In these systems, the rate of drug release from the microcapsules was found to be linearly related to the surface tension of the dissolution medium in the range of 40-60 dyn/cm (x 10(-3) N/m). In the same surface tension range, the effect of aerosol OT on rate increase was found to be much less than those of the cationic and nonionic surfactants. This suggests that the anionic surfactant is not well adsorbed at the interface due to the negative charge characteristics of the surface of the polylactic acid microcapsules. However, at nearly the critical micelle concentration of aerosol OT, where the corresponding surface tension is much lower than those of the cationic and nonionic surfactants, the microcapsules exhibited the highest rate of drug release.