Importance

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Abstract

An osmotically driven syringe (20, 60) is disclosed which can be used to deliver a beneficial agent such as a drug, at varying pre-determined rates over multiple periods of time. The syringe (20, 60) is driven by an osmotic engine (10) having a shaped wall (12) containing an osmotic agent (17) and/or a gas generating means (19), such as an effervescent couple. The wall (12) is composed of a semipermeable and/or microporous material which is permeable to an external liquid (e.g., water) but which is substantially impermeable to the osmotic agent (17) and the gas generated by the gas generating means (19). The wall (12) has a passageway (13) therethrough to provide a flow path for the driving fluid generated by the engine (10). The osmotic agent(s) (17) and/or the gas generating means (19) are placed in the engine (10) in such a way as to drive engine (10) at different pumping rates (R.sub.1, R.sub.2) over sequential periods of time (t.sub.o to t.sub.1 and t.sub.1 to t.sub.2).

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First Claim