Patent ID: 7883722

Claim:
A composition for controlled delivery of at least one drug into an aqueous medium by erosion at a preprogrammed rate of at least one surface of the composition, the composition comprising (A) a matrix which is erodible in the aqueous medium in which the composition is to be used and which allows substantially no diffusion of water into the composition beyond any exposed surface layers of the matrix, wherein the matrix comprises, substantially homogeneously distributed in the matrix, (i) at least one drug, (ii) at least one substantially water soluble crystalline polymer with at least one water-dispersible or water-soluble surface active agent dispersed therein, and (iii) at least one material that is water soluble at a pH in the range of from about 5 to about 7 and substantially water-insoluble at lower pH values, wherein the material is selected from the group consisting of polyvinyl acetate phthalate, hydroxypropyl methylcellulose phthalate, and hydroxypropyl methylcellulose acetate succinate copolymers, wherein the material is present in an amount of about 0.1-10%, based on the weight of the matrix, and provides the composition with a pH-dependent release of the at least one drug, and (B) a coating on the matrix having at least one opening exposing at least one surface of the matrix, the coating being one which crumbles and/or erodes upon exposure to the aqueous medium at a rate which is equal to or slower than the rate at which the matrix erodes in the aqueous medium, allowing exposure of said surface of the matrix to the aqueous medium to be controlled.