Novel drug permeable wall

In a drug delivery device for continuously administering a drug at a controlled rate for a prolonged period of time to a body site, said device comprising a reservoir containing said drug and a carrier permeable to said drug, the amount of said drug being sufficient to maintain saturation within said carrier during said prolonged period, and a wall surrounding said reservoir which is permeable to the drug but at a rate less than that of the carrier, whereby the drug is released from the reservoir by diffusion through the wall in which the drug dissolves in the material forming the wall and moves therethrough in the direction of lower chemical potential, the improvement comprising forming the wall from a composition comprising a mixture of:

• A. a polymer which is rubbery with a glass transition temperature below about 20.degree.C, or is glassy having a glass transition temperature between about 20.degree.C and about 150.degree.C, or has a crystallinity between about 5% and about 95%;
• and
• B. a polymeric additive which is essentially insoluble in body fluids, is nonvolatile and nonleachable and nonextractable from the polymer under the use conditions of the composition and is selected from the group consisting of:
• a. essentially linear olefinically saturated polyesters having a number average molecular weight of about 500 to about 8,000 of a diol of 2 to about 7 carbon atoms or polyethylene glycol and a dibasic carboxylic acid of about 6 to about 15 carbon atoms in which the terminating group is a carboxyacyl group of about 2 to about 18 carbon atoms or an alkoxy group of about 3 to about 15 carbon atoms;
• b. polyethylene glycols of about 200 to about 1,500 molecular weight;
• c. ethylene-vinyl acetate copolymers of about 20% to about 40% by weight vinyl acetate and about 20,000 to about 30,000 number average molecular weight;
• d. chlorinated polyethylene of about 25% to 45% by weight chlorine and about 20,000 to about 30,000 number average molecular weight;
• e. ethylene-ethylacrylate copolymers of about 20% to about 40% by weight ethylacrylate and about 20,000 to about 30,000 number average molecular weight;
• and
• f. ethylene-vinyl chloride copolymers of about 25% to about 45% by weight chlorine and about 20,000 to about 30,000 number average molecular weight, the amount of additive in the mixture being sufficient to make the permeability of the composition of the drug substantially different than the permeability of the polymer to drug but less than the permeability of the carrier to drug, said composition being biologically compatible with the site, essentially non-erodible, essentially insoluble in body fluids, and, if the drug is highly water soluble, substantially impermeable to water to essentially prevent dilution of the drug by absorption of body fluids into the reservoir.