Osmotic devices having composite walls

Claim 1

An osmotic device for dispensing a drug to an animal comprising: (a) a shaped wall that is substantially inert and maintains its physical and chemical integrity during the controlled dispensing of the drug comprising: (1) a semipermeable wall forming material that is permeable to the passage of an external fluid and substantially impermeable to the passage of the drug, said semipermeable material being a polymer of the following formula ##STR4## wherein R 1 , R 2 , and R 3 are selected from the group consisting of hydrogen, alkyl, alkenyl, and acyl and n is greater than 5, and (2) a stabilizing material that imparts inertness and stability to the wall, and which stabilizing material is a different polymer of the following formula: ##STR5## wherein R 5 is a member selected from the group consisting of hydroxyl, alkoxy, hydroxyl-substituted alkoxy, alkylcarbonate, alkylcarbamate, alkylsulfonate, alkylsulfamate, and acyloxy, and n is greater than 5; (b) a compartment formed by the shaped wall and containing the drug, said drug being a member selected from the group consisting of locally and systemically acting drugs; (c) a passageway in the wall communicating with the compartment and the exterior of the device for dispensing the drug from the device; and, (d) wherein in operation when the device is dispensing the drug to the animal, fluid therefrom is continuously imbibed through the wall into the compartment in a tendency towards osmotic equilibrium at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall, thereby forming a solution containing drug which is dispensed through the passageway at a controlled rate, with the wall substantially maintaining its inertness and integrity in the presence of the drug and solution thereof over a prolonged period of time.