Modelling of drug release from coated granular pellets.

A mathematical model of drug release from coated pellets with a granular core has been developed. The model includes a dynamic description of all three main processes contributing to drug release from such a system, i.e. liquid inflow, drug dissolution, and liquid efflux caused by diffusion across the coating. The cumulative fraction of released drug has been shown to be determined by three rate constants, one for each process mentioned above, together with two dimensionless parameters. These parameters are related to the porosity of the pellet core and the solubility of the drug in the dissolution medium. The model has been validated by comparison with experimentally determined release profiles for pellets consisting of a granular core of microcrystalline cellulose containing dispersed salicylic acid, coated by a thin layer of ethyl cellulose.