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Osmotic delivery system having space efficient pistonRelated Patent Categories: Surgery, Controlled Release Therapeutic Device Or System, Osmotic Or Diffusion Pumped Device Or SystemOsmotic delivery system having space efficient piston description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070203476, Osmotic delivery system having space efficient piston. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS [0001] This application is a continuation of application Ser. No. 11/353,842, filed Feb. 14, 2006, which application is a continuation of application Ser. No. 10/959,489, filed Oct. 5, 2004, now U.S. Pat. No. 6,997,922, issued Feb. 14, 2006, which application is a continuation of application Ser. No. 10/354,142, filed Jan. 30, 2003, now U.S. Pat. No. 6,872,201, issued Mar. 29, 2005, which is a continuation of, and claims priority from U.S. patent application Ser. No. 09/472,600, filed Dec. 27, 1999, now U.S. Pat. No. 6,544,252, issued Apr. 8, 2003, which claims the benefit of U.S. Provisional Application Ser. No. 60/114,548, filed on Dec. 31, 1998, the entire disclosures of which are hereby incorporated herein by reference in their entireties. FIELD OF THE INVENTION [0002] The present invention relates to osmotic delivery systems for delivering beneficial agents, and more particularly, to an osmotic delivery system having a piston with a recess for receiving an osmotic agent. BACKGROUND OF THE INVENTION [0003] Description of the Related Art: Controlled delivery of beneficial agents, such as drugs, in the medical and veterinary fields, has been accomplished by a variety of methods. One method for controlled prolonged delivery of beneficial agents involves the use of osmotic delivery systems. These devices can be implanted to release beneficial agents in a controlled manner over a preselected time or administration period. In general, osmotic delivery systems operate by imbibing liquid from the outside environment and releasing corresponding amounts of the beneficial agent. [0004] A known osmotic delivery system, commonly referred to as an "osmotic pump," generally includes some type of capsule or enclosure having a semipermeable portion that may selectively pass water into an interior of the capsule that contains a water-attracting osmotic agent. In such a known osmotic delivery system, the walls of the capsule are substantially impermeable to items within and outside the capsule, and a plug acts as the semipermeable portion. The difference in osmolarity between the water-attracting agent and the exterior of the capsule causes water to pass through the semipermeable portion of the capsule, which in turn causes the beneficial agent to be delivered from the capsule through the delivery port. The water-attracting agent may be the beneficial agent delivered to the patient. However, in most cases, a separate osmotic agent is used specifically for its ability to draw water into the capsule. [0005] In some instances, a piston is required to separate the beneficial agent from the osmotic agent to prevent the osmotic agent from mixing with or contaminating the beneficial agent. The structure of the capsule is such that the capsule does not expand when the osmotic agent takes in water and expands. As the osmotic agent expands, pressure causes the piston to move and the beneficial agent to be discharged through the delivery orifice at the same rate as the liquid, which is typically water, enters the osmotic agent by osmosis. Osmotic delivery systems may be designed to deliver a beneficial agent at a controlled constant rate, a varying rate, or in a pulsatile manner. [0006] In those osmotic delivery systems that require the use of a piston to separate the beneficial agent and the osmotic agent, the piston necessarily occupies space in the capsule. Hence, if the piston is needed to separate the beneficial agent and the osmotic agent, and the size of the capsule is not changed, the amount of beneficial agent or osmotic agent that can be held within the capsule decreases as compared to another osmotic delivery system having the same size capsule that does not include a piston. Decreasing the amount of beneficial agent within the capsule detrimentally decreases the net amount of beneficial agent that can be delivered over a sustained period of time. Decreasing the amount of osmotic agent within the capsule detrimentally decreases the sustained period of time through which continuous delivery of the beneficial agent can be obtained. [0007] But if the specific application requires a specific amount of beneficial agent or osmotic agent that cannot be varied and a piston must be used to separate the beneficial agent from the osmotic agent, the size of the capsule must be increased to accommodate for the extra space occupied by the piston such that the amount of osmotic agent or beneficial agent in the capsule does not vary. While simply increasing the size or volume of the capsule to accommodate for the extra volume occupied by the piston may appear to be a simple solution, because many osmotic delivery systems are destined for implantation in humans or animals, it is especially desirable to decrease the size of the osmotic delivery system as much as possible, while still allowing the osmotic delivery system to deliver the beneficial agent over a prolonged period of time. Additionally, simply increasing the size of the capsule for those applications requiring a piston that separates the beneficial agent from the osmotic agent is inexpedient as it is desirable to use one capsule for multiple osmotic delivery system applications. Moreover, it has been particularly problematic to increase the amount of time over which steady state release of the beneficial agent may be obtained with current osmotic delivery systems incorporating conventional pistons, without increasing the size of the capsule to hold more beneficial agent or osmotic agent. These problems associated with current osmotic delivery systems having known pistons have created a need for a solution. BRIEF SUMMARY OF THE INVENTION [0008] In accordance with one aspect of the present invention, an osmotic delivery system includes an enclosure having an interior for holding a protein or peptide. An osmotic agent is located in the enclosure, and a semipermeable body is in liquid communication with the enclosure for permitting liquid to permeate through the semipermeable body to the osmotic agent. The system also includes a piston located within the enclosure, the piston defining a movable seal with the enclosure that separates the osmotic agent from the protein or peptide. The piston has a recess that receives a sleeve. The sleeve has an interior that receives at least a portion of the osmotic agent. The osmotic agent is located between the piston and the semipermeable body, the osmotic agent adapted to imbibe liquid from a surrounding environment through the semipermeable body to cause the piston to move and cause delivery of the protein or peptide from the enclosure. [0009] In accordance with another aspect of the present invention, an osmotic delivery system includes a piston located within an enclosure, the piston having a recess. The system also includes an osmotic agent located within the recess, the osmotic agent adapted to imbibe liquid from a surrounding environment to cause the piston to move within the enclosure and displace the contents of the enclosure. [0010] According to another aspect of the present invention, a piston for use in an osmotic delivery system that has an enclosure and a semipermeable body in communication with the enclosure includes a sleeve located within a recess in the piston, the sleeve having an interior. An osmotic agent is at least partially contained in the sleeve and is located between the piston and the semipermeable body. The osmotic agent is adapted to imbibe liquid from a surrounding environment through the semipermeable body to cause the piston to move and cause delivery of the beneficial agent from the enclosure. [0011] Other objects, advantages and features associated with the present invention will become readily apparent to those skilled in the art from the following detailed description. As will be realized, the invention is capable of other and different embodiments, and its several details are capable of modification in various obvious aspects, all without departing from the invention. Accordingly, the drawings and the description are to be regarded as illustrative in nature, and not limiting. BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS [0012] The invention will be described in greater detail with reference to the accompanying drawings in which like elements bear like reference numerals, and wherein: [0013] FIG. 1 is a sectional view of an osmotic delivery system according to one embodiment of the present invention; [0014] FIG. 2 is a sectional view of an osmotic delivery system according to the present invention taken along the line 2-2 of FIG. 1; [0015] FIG. 3 is a perspective view of a piston according to one embodiment of the present invention; [0016] FIG. 4 is an exploded perspective view of an osmotic delivery system according to one embodiment of the present invention; [0017] FIG. 5 is a sectional view of another osmotic delivery system according to the present invention; [0018] FIG. 6 is a perspective view of a cup-shaped sleeve for insertion into a recess of a piston in accordance with another embodiment of the present invention; [0019] FIG. 7 is sectional view of the sleeve of FIG. 6 taken along the line 7-7 of FIG. 6. 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