Swellable matrices for controlled drug delivery: gel-layer behaviour, mechanisms and optimal performance.

The majority of oral drug delivery systems (DDS) are matrix-based. Swellable matrices are monolithic systems prepared by compression of a powdered mixture of a hydrophilic polymer and a drug. Their success is linked to the established tabletting technology of manufacturing. Swellable matrix DDS must be differentiated from true swelling-controlled delivery systems. This review focuses on hydrophilic swellable matrix tablets as controlled DDS. Gel-layer behaviour, front movement and release are described to show the dependence of the release kinetics on the swelling behaviour of the system. In vivo behaviour of matrix systems is also considered.