ASYMMETRIC-MEMBRANE TABLET COATINGS FOR OSMOTIC DRUG-DELIVERY

A new type of membrane coating has been developed for osmotic drug delivery that offers significant advantages over the membrane coatings used in conventional osmotic tablets. These new coatings have an asymmetric structure, similar to asymmetric membranes made for reverse osmosis or ultrafiltration, in that the coating consists of a porous substrate with a thin outer skin. These asymmetric-membrane coatings can be used to make osmotic drug-delivery formulations with several unique characteristics. High water fluxes can be achieved, facilitating osmotic delivery of drugs with low solubilities and making higher release rates possible. The permeability of the coating to water can be adjusted by controlling the membrane structure, thereby allowing control of the release kinetics without altering the coating material or significantly varying the coating thickness. In addition, the porosity of the skin can be controlled, minimizing the time lag before drug delivery begins and allowing the drug to be released from a large number of delivery ports. The use of asymmetric-membrane coatings on pharmaceutical tablets is described in this paper; the coatings have also been applied to capsules and multi-particulate formulations.