An MRI analysis of the dissolution of a soluble drug incorporated within an insoluble polymer tablet

Magnetic resonance imaging is used to map the ingress of water into a nominally non-swelling polymer-matrix slow-release drug delivery device comprising a compact of particulate Eudragit polymer and Diltiazern Hydrochloride drug. It is shown that the water ingresses with the square root of time: that is, it is "Fickian-like"; and that the release depends only weakly on the particulate size. A dissolution-diffusion model specifically incorporating the drug particulate size is developed to describe the release mechanism. The experimental results are in accord with the model. It is further shown theoretically that the release should become "non-Fickian-like" and particle size dependent if the drug dissolution constant were to be reduced substantially, an observation explained using a dimensionless scaling argument that compares the dissolution and diffusion rates. It has, however, not been possible to perform experiments in this different regime with the same materials.