Preparation and Release Property of Polylactic Acid Microspheres Containing Slightly Water-soluble Drug.

Polylactic acid (PLA) microspheres containing theophylline as a slightly soluble representative drug were prepared using the o/w emulsion in-water drying method. A high trapping efficiency was observed when polymer solution of high concentration was used and the drug/polymer weight ratio was increased. However, the particle size of the microspheres became extremely large when the high concentration polymer solution was used.Microspheres with a particle size of 88.6 μm were obtained when “ sub-emulsification” was performed with the external aqueous phase with an equal specific gravity to the polymer solution. On the other hand, the trapping efficiency of the microspheres was dependent on both the drug encapsulated in the microspheres and the particle size of microspheres.The release patterns of the drug from the microspheres showed an initial-burst release in all batches. The release rates of the drug from the microspheres prepared with the drug and polymer alone were very small. Therefore, an improvement in the drug release property of the microspheres was examined.The release rates of the drug from the microspheres increased si gnificantly depending on the amount of ethyl myristate that was incorporated as a release promoter.