Swelling and drug release behaviour of xanthan gum matrix tablets

The swelling and drug release behaviour of xanthan gum matrix tablets were studied using three drugs having different properties, i.e., caffeine as a soluble neutral drug, indomethacin as an insoluble acidic drug, and the sodium salt of indomethacin as a soluble acidic drug. Swelling was ascertained by measuring the axial and the radial expansion of matrix tablets following exposure to media of physiological ionic strength. The mean drug dissolution time and swelling rate were calculated from dissolution and swelling experiments, respectively, and were used as responses for comparison under different experimental conditions. The dependence of drug release on the swelling of the polymer matrix and on the type of the drugs added was established. The former is mainly influenced by the ionic strength and buffer concentrations. The latter is affected by the solubility of the drug. The mechanism of matrix swelling follows Case I diffusion, whereas drug release from this polymer matrix conforms to Case II diffusion.