Compressed xanthan and karaya gum matrices: hydration, erosion and drug release mechanisms

Directly compressed matrices were produced containing either xanthan gum or karaya gum as a release-controlling agent. These swellable hydrophilic nat ural gums were used to control the release of varying proportions of two mo del drugs, caffeine and diclofenac sodium, which have different solubilitie s in aqueous medium. Gum erosion, hydration and drug release studies were c arried out using a dissolution apparatus (basket method) at two agitation s peeds. Xanthan gum displayed a high degree of swelling due to water uptake and a small degree of erosion due to polymer relaxation. Neither agitation speed nor drug solubility had any significant effect on water uptake, but m atrices with the lower proportion of gum produced a lesser degree of hydrat ion. In contrast, karaya gum displayed a much lower hydration capacity and a higher rate of erosion, both markedly affected by agitation speed. Drug r elease from xanthan and karaya gum matrices depended on agitation speed, so lubility and proportion of drug. Both xanthan and karaya gums produced near zero order drug release with the erosion mechanism playing a dominant role , especially in karaya gum matrices. (C) 2000 Elsevier Science B.V. All rig hts reserved.