RELATIONSHIP BETWEEN SWELLING, EROSION AND DRUG-RELEASE IN HYDROPHILIC NATURAL GUM MINI-MATRIX FORMULATIONS

The swelling, erosion and solvent front penetration properties of mini -matrices containing xanthan (X), locust bean (LB) and karaya (K) gums were examined, analysed and related to the overall in vitro release k inetics of diclofenac sodium, used as a model drug. Mini-matrices were produced with drug:gum ratios of 1:1 as well as formulations of drug and X in combinations of 2:1, 2:3 and 1:2. The rank order of decreasin g swelling index (SI) in both axial and radial dimensions was X>K>LB a nd each gum showed almost Fickian swelling behaviour. The solvent fron t penetration rates were consistent with the rates of swelling. Howeve r, the order of decreasing drug release and erosion rates was LB>X>K a nd all formulations demonstrated anomalous (non-Fickian) drug release kinetics. Therefore Fickian drug diffusion and polymer erosion were bo th occurring simultaneously. The dominant mechanism depended on the na ture and content of the gum, as well as the stage in the dissolution t ime period. There was a loss of matrix integrity in formulations conta ining a high drug:gum ratio. (C) 1998 Elsevier Science B.V.