A mechanism on the drug release into a perfect sink from a coated planar matrix with a super-saturation loading in the core.

A comprehensive model is proposed to accurately describe drug release kinetics from a coated plane sheet when drug loading in the core is above its saturation level. The general solutions are acquired in a dimensionless form by the Laplace transform and the solution for the special case-a perfect sink condition, is derived from these general ones. On the basis of the model calculations, the effects of the diffusion ratios and thickness ratios of the coatings to the core, and drug loading entrapped in the core during the release processes have been discussed over wide range of variables. To validate the model equations proposed, the coated systems, 5-fluoracilum/ethylene-vinyl alcohol copolymer (5-Fu/EVAL) core matrix coated with various polymeric materials such as EVAL, cellulose acetate (CA), poly(2-hydroxyethyl methacrylate) (PHEMA) and poly( methyl methacrylate) (PMMA), having different diffusivities, are designed, experimentally investigated and graphically and quantitatively compared with the theoretical values. The results show a good correlation between the theory and experiment.