Analysis of the swelling and release mechanisms from drug delivery systems with emphasis on drug solubility and water transport

The movement of the penetrant and polymer fronts and the drug dissolution in highly loaded swellable matrix tablets were studied with the aim of establishing relationships between front position and drug release kinetics. Three boundaries were identified corresponding to the swelling, diffusion and erosion fronts. The kinetics of drug release depended on the relative movement of the erosion and swelling/diffusion fronts. Under certain conditions of drug solubility and loading in the matrix, the last two could move separately. The data obtained demonstrated that the difference between the diffusion and erosion fronts is decisive for the release kinetics. This leads to a new finding that the distance between diffusion and erosion fronts (dissolved drug gel layer thickness) is the most important parameter for drug release, instead of the distance between swelling and erosion fronts (whole gel layer thickness).