| 摘要 |
An osmotically driven pump is provided that is capable of being miniaturized to a size suited for swallowing or implanting in an animal. The pump may be used to administer a drug in fluid form after an initial activation period during which substantially no drug is administered. The basic components of the pump are a shaped semipermeable membrane that encapsulates an osmotically effective solute and preferably a drug or other beneficial agent and a discharge port through which the drug or other beneficial agent is dispensed. A semipermeable or microporous outer cover surrounds the semipermeable membrane and seals it from an external aqueous environment. A water-swellable composition is operatively positioned between the end of the semipermeable membrane and the outer cover. Preferably, a water wicking layer at least partially surrounds the semipermeable membrane and is also sealed within the outer cover. In operation, the pump is placed in an aqueous environment. Water from the environment passes through the semipermeable/microporous portion of the outer cover into the water-swellable composition. The water-swellable composition absorbs water, expands, and in piston-like fashion displaces the outer cover, thereby exposing the semipermeable membrane to the aqueous environment and activating the osmotic pump. The time required for the water-swellable composition to absorb water, expand and displace the outer cover provides an initial activation period during which substantially no drug is delivered by the pump.
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