United States Patent:   5,997,527

Assignee:  ALZA Corporation (DE)

Filed:  March 23, 1998

A delivery device having a first chamber containing an osmotic agent, a membrane forming a wall of the first chamber through which fluid is imbibed by osmosis, a second chamber containing a beneficial agent to be delivered, and a moveable piston separating the two chambers. In fluid communication with the second chamber is an orifice which comprises a slit valve. In the presence of pressure, the beneficial agent pushes through the slit, opening up a channel for delivery of the beneficial agent and creating flow. Because the slit remains closed in the absence of flow (or when the pressure is below the pressure required to open the slit), back diffusion of external fluids is eliminated when the slit is closed, which prevents contamination of the beneficial agent in the second chamber by external fluids. In addition, forward diffusion of the beneficial agent out of the capsule is prevented when the slit is closed. The slit valve opens only to the minimum dimension required to allow the flow generated by the osmotic pumping rate. The slit valve also allows a flow path to open around any obstruction in the slit valve to prevent clogging.

SUMMARY OF THE INVENTION

According to one embodiment of the invention, an exemplary delivery device, such as described in U.S. patent application Ser. No. 08/595,761, the entire disclosure of which is incorporated herein by reference, may be provided with the slit orifice of the present invention. The delivery device comprises a capsule containing a beneficial agent and an osmotic agent, a membrane which forms a portion of a wall of the capsule, the membrane allowing fluid from an external environment to pass into the capsule by osmosis to create an osmotic pressure in the capsule, means for applying the osmotic pressure to the beneficial agent, and a flexible member having therein a slit orifice which is in fluid communication with the capsule.

In the presence of flow, the beneficial agent pushes through the slit, opening up a channel for delivery of the beneficial agent. Because the slit orifice remains closed in the absence of flow, back diffusion of external fluids is eliminated when the slit is closed, which prevents contamination of the beneficial agent by external fluids. Forward diffusion of the beneficial agent out of the capsule is also prevented.

In addition, the slit orifice allows a flow path to open around an obstruction in the slit orifice. In the event that a suspended particle becomes lodged in the slit orifice, a new flow path is created around the obstacle, thereby preventing clogging. The slit orifice is also very compact and easily fits inside the delivery device, which is advantageous when the delivery device is implanted subcutaneously.

This combination uniquely addresses the complex issues presented in the extremely low flow, high osmolar drug delivery systems as found, for example, in U.S. patent application Ser. No. 08/595,761. These issues include drug diffusion out of the orifice, back diffusion of liquid from the environment of use into the orifice, and clogging of the orifice, especially if the orifice is small enough to eliminate drug diffusion and back diffusion.

Claim 1 of 28 Claims

1. A delivery device comprising:

a capsule having an opening, said capsule containing a beneficial agent and an osmotic agent;

at least a portion of the capsule being permeable to fluid from an external environment to allow the fluid to pass into the capsule by osmosis to create an osmotic pressure in the capsule;

means for applying the osmotic pressure to the beneficial agent; and

a flexible plug at least partially located in said opening of said capsule, at least a portion said flexible plug located in said opening being in a state of compression through application of a compressive force, said flexible plug having therein at least one slit orifice which is in fluid communication with the capsule, the slit orifice being closed when a pressure of the beneficial agent is less than a predetermined pressure, said slit orifice having a portion not subjected to said compressive force.

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