A kinetic model for predicting the release rate of sparingly-water-soluble drugs from a hydrogel-coated polymeric matrix

Medical devices used for on-target drug delivery are often coated with a hydrogel coating for friction-reduction purpose. Thus, the delivery of a sparingly-water-soluble drug by such a device must diffuse through a nonerodable hydrogel layer. An empirical rate equation has been derived for such a kinetic model and predicts that the rate of drug release from such a device is directly proportional to the loading of the drug in the polymeric matrix. The validity of this kinetic model was examined by measuring the rate of release of 2,4,4'-trichloro-2'-hydroxydiphenyl ether from different hydrogel-coated (ethylene-vinyl acetate) copolymer stents containing a wide range of the drug. The experimentally determined release rates are in reasonably good agreement with those calculated from the empirical rate equation. Bioefficacy test results based on zone-of-inhibition test against Escherichia coli are also in good agreement with the release rate and drug-loading data predicted according to the empirical rate equation.