The effect of buffer concentration, pH and buffer ions on the degradation and drug release from polyglycolide

Samples of polyglycolide were degraded in various buffered solutions in order to investigate the effects of buffer concentration, pH and particular buffer ions on the hydrolysis reaction. The small-angle X-ray scattering profiles changed with degradation; long periods were calculated and their changes with degradation used as a measure of the degradation rate. The release of a model drug, theophylline, was also investigated under these different buffering conditions. In more concentrated buffer solutions theophylline was released slightly earlier and the samples began to swell sooner. Increasing the pH of the phosphate buffer also resulted in an earlier swelling and release of drug. These effects were attributed to the neutralisation and increased solubility of acidic degradation products in more concentrated or alkaline buffer solutions. When an imidazole-HCl rather than a phosphate or citrate-citric acid buffer system was used, swelling and drug release were accelerated, as imidazole catalysed the ester hydrolysis reaction. The results are interpreted within the context of a four-stage model of PGA degradation. (C) 2003 Society of Chemical Industry.