Membrane-coated sustained-release tablets and method

Claim 1

Method of producing a sustained-release coated pharmaceutical tablet comprising a drug-containing tablet and a coating or membrane surrounding the same, wherein the coating or membrane is water-insoluble and insoluble in gastrointestinal fluids and consists essentially of a terpolymer of polyvinylchloride, polyvinylacetate and polyvinylalcohol and a water-soluble pore-creating substance, the said pore-creating substance being randomly distributed in said terpolymer coating, said pore-creating substance being present in amount of one part to 35 parts for each one to ten parts of terpolymer, said coated tablet exhibiting a substantially constant dissolution rate during a major portion of its dissolution time when exposed to gastrointestinal fluids, comprising the steps of providing said terpolymer and dissolving the said terpolymer in a solvent, preparing a suspension or solution of the pore-creating substance, providing a pharmaceutical tablet, combining the suspension or solution of pore-creating substance and solvent solution of the terpolymer to form a coating fluid, applying the coating fluid in the form of a solution or suspension to the tablet, and drying the coating fluid on the tablet to provide a terpolymer-coated tablet having water-soluble pore-creating substance randomly distributed within the coating or membrane, wherein the terpolymer contains about 80 to 95% weight per weight of polyvinylchloride, 0.5 to 19% weight per weight of polyvinylacetate, and 0.5 to 10% weight per weight of polyvinylalcohol.