Abstract

An osmotic device is disclosed for dispensing a drug. The device comprises an exterior wall surrounding a first and second compartment. The first compartment is in contact with the exterior wall and the second compartment is surrounded by an interior wall that is in contact with the exterior wall. A passageway exists through the exterior wall connecting the first compartment with the exterior of the device, and a passageway exists through the interior wall connecting the second with the first compartment. The first compartment contains an osmotic solute that exhibits an osmotic pressure gradient across the wall against an external fluid, and the second compartment contains a drug that exhibits an osmotic pressure gradient across the wall against the fluid. The exterior and the interior walls are permeable to the passage of the fluid, and they are impermeable to the passage of solute and drug, but the rate of fluid, permeability is greater through the exterior than through the interior wall. In operation, fluid in imbibed through the walls into the compartments and at a greater rate into the first compartment forming a more dilute solution therein than the drug solution formed in the second compartment, said drug solution passing from the second compartment through the passageway into the compartment and being diluted in the first compartment, with the diluted drug solution passing from the first compartment through the passageway to the exterior of the device.