SWELLING AND DRUG-RELEASE IN HYDROGEL MATRICES - POLYMER VISCOSITY AND MATRIX POROSITY EFFECTS

Hydroxypropylmethylcellulose (HPMC) represents the most frequently use d polymer in the formulation of hydrogel matrices for controlled drug delivery. Drug release from these matrices is related to the area expo sed to the dissolution medium. This work focused on the release of buf lomedil pyridoxalphosphate from hydrogel matrices containing HPMC havi ng different grades of viscosity and partially coated with an impermea ble film. Drug release was discussed as a function of the dimensional modification of the matrices during release. It was found that the rel ease kinetics is controlled by the increase in releasing area produced by the swelling phenomenon. The presence of an impermeable coating on the hydrogel matrix changes the swelling kinetics, and as a consequen ce the systems can become more liable to erosion. Drug release is slig htly influenced by the viscosity of the polymer. The initial porosity of the hydrogel matrices, in the range studied, does not affect drug r elease.