Some determinants of morphology and release rate from poly()lactic acid microspheres

Abstract

Morphology and release rate from poly()lactic acid microspheres were studied as a function of drug loading, drug lipophilicity and solvent evaporation rate. Sudan III was used to exemplify lipophilic compounds, while etoposide served as a relatively polar drug. Drug loading was found to be an important determinant of morphology, with increased formation of distorted microspheres at higher loadings. In the case of the polar etoposide, this translated into a greater release rate. For Sudan III, however, negligible release occurred despite morphological changes, suggesting that the drug lipophilicity is also important as a determinant of release rate. When gelatin was used as the emulsifying agent, the percentage of distorted microspheres and the release rate were highly dependent on the rate of solvent evaporation. When smooth microspheres were produced with polyvinyl alcohol as the emulsifying agent, drying rate was found to be of less importance.