Factors affecting the degradation rate of poly(lactide-co-glycolide) microspheres in vivo and in vitro

The purpose of this work was to study the degradation of poly(lactide-co-gl ycolide) (PLG) microspheres in vivo and in vitro. Degradation rate constant s were determined by measuring the polymer molecular weight as a function o f time by gel-permeation chromatography. The effects of PLG chemistry and t he effects of encapsulating the sparingly soluble salt zinc carbonate and t he protein recombinant human growth hormone (rhGH) on the degradation rate were assessed. It was found that in vivo degradation was faster than in vit ro degradation. In addition, different types of PLGs were found to degrade at different rates depending on the chemistry of the polymer end group and, to a lesser extent, the molecular weight. Finally, zinc carbonate was foun d to retard the degradation of some PLGs. These degradation studies have pr oved valuable in the design of sustained release microsphere products. (C) 1999 Elsevier Science Ltd. All rights reserved.