Osmotic devices for delivering a beneficial agent to an environment of use are known to the prior art in U.S. Pat. Nos. 3,845,770 and 3,916,899. The devices disclosed in these patents are made with a wall formed of a material that is permeable to an external fluid and substantially impermeable to agent. The wall surrounds a compartment that contains an agent and there is a passageway through the wall for dispensing the agent. These devices are remarkably effective for delivering an agent that is soluble in the fluid and exhibits an osmotic pressure gradient across the wall against the fluid, and for delivering an agent that has limited wall against the fluid, and for delivering an agent that has limited solubility in the fluid and is admixed with an osmotically effective compound soluble in the fluid that exhibits an osmotic pressure gradient across the wall against the fluid. The devices release agent by fluid being continuously imbibed through the wall into the compartment at a rate determined by the permeability of the wall and the osmotic pressure gradient across the wall to produce a solution of soluble agent, or a solution of soluble compound containing agent which solution in either operation is dispensed from the device. While the above devices represent a significant and pioneer advancement in the art and they are useful for dispensing numerous agents, there is an occasional instance where the agent may have an unwanted effect on the device. For example, a wall formed of cellulose acetate having a low acetyl content in the presence of certain agents can slowly lose its integrity over a prolonged period of time thereby slowly changing the rate of imbibition and concomitantly the rate of agent release from the device over a correspondingly prolonged period of time.
USPTO Backgrounds
USPTO Backgrounds