Patent ID: 7655257

Claim:
An implantable, fluid-imbibing device for delivering an active agent to a fluid environment of use, said device comprising the following components: an impermeable reservoir comprising an interior surface; a piston that divides the reservoir into a water-swellable agent chamber and an active agent chamber, wherein the water-swellable agent chamber has an open end and the active agent formulation chamber has an open end; a back diffusion regulating outlet received in the open end of the active agent formulation chamber of the reservoir for delivering fluid from the active agent formulation chamber to the fluid environment, the reservoir interior surface and back diffusion regulating outlet having surfaces in a mating relationship, wherein (i) a helical flow path for the active agent is formed between the mating surfaces, (ii) a length of the helical flow path is sufficient to prevent back-diffusion of external fluid through the helical flow path, and (iii) the helical flow path has a length of about 2 to about 7 cm; and a water-swellable semipermeable plug received in sealing relationship with the interior surface of the open end of the water-swellable agent chamber of the reservoir.