Controlled release drug formulation of open end cylindrical rod form

A method for controlling the rate of release of a drug from a drug formulation in the form of a cylindrical rod by controlling water infiltration into the drug formulation wherein said drug formulation has an axial length and comprises

• (a) a nondisintegrating inner layer having a cross-sectional diameter and a circumference wherein said inner layer is comprised of a biocompatible hydrophobic material selected from the group consisting of polyesters, polyamino acids, silicones, ethylene-vinyl-acetate copolymers and polyvinyl alcohols that contains at least one uniformly dispersed water-soluble drug as the only active agent(s), and
• (b) an outer layer comprised of a biocompatible hydrophobic polymer wherein said outer layer surrounds the circumference of the inner layer and the outer layer is impermeable to water and is capable of controlling the swelling of the inner layer;
• wherein the ratio of the axial length of the drug formulation to the cross-sectional diameter of the inner layer is one or more and at least one end of the inner layer is open so as to come into contact with any external environment, and wherein the drug is released at a controlled rate over a prolonged period of time exclusively through said open end.