An investigation of the synthesis of poly(D,L-lactic acid) and preparation of microspheres containing indomethacin

Seven batches of poly(D,L-lactic acid) (PLA) were prepared from D,L-lactic acid using tetraphenyltin or zinc acetate as a catalyst. The samples of PLA were characterized by terminal group analysis, gel permeation chromatography, infrared analysis, and differential scanning calorimetry. Polymerization conditions such as the time of reaction and the type of catalyst affected the molecular weight of PLA. Microspheres containing indomethacin were prepared by the oil/water (o/w) solvent evaporation technique using different formulations and process variables. The in vitro release of indomethacin in phosphate buffer was found to be dependent on the molecular weight of PLA and also on the type and amount of adjuvants used. The batch of microspheres containing 5% cholesterol released the drug at a slow controlled rate (29%, 65%, and 85% in 1, 7, and 24 hr, respectively). The results of F test for the microspheres revealed that there is no significant difference between the Higuchi model and the power law equation. The drug was released by a diffusion mechanism from the microspheres.