WO1994005354A1

WO1994005354A1 - Fluid driven dispensing device

Info

Publication number: WO1994005354A1
Application number: PCT/US1993/008502
Authority: WO
Inventors: John Urquhart; Terry L. Burkoth; J. Richard Gyory; Paul R. Magruder; Dominic A. Ventura; Charles F. Albert; Su Il Yum
Original assignee: Alza Corporation
Priority date: 1992-09-09
Filing date: 1993-09-09
Publication date: 1994-03-17
Also published as: AU4853793A; MX9305545A; ZA936662B

Abstract

A fluid driven dispensing device (10) in which a piston (14) driven by the fluid discharged from an engine (38) moves a plunger (26) to displace the contents of the syringe. The cross-sectional area of the plunger (26) is greater than the area of the piston (14) exposed to the driving fluid so that a given volume of fluid discharged from the pump will displace a larger volume of beneficial agent from the syringe. Means are also provided for directing fluid discharged from the engine away from the piston to permit on/off operation of the syringe.

Description

FLUID DRIVEN DISPENSING DEVICE

TECHNICAL FIELD This invention pertains to a fluid driven dispensing device for delivering a beneficial agent to an environment of use, and in particular to a device where the effect of a given volume of driving fluid is amplified to deliver a greater volume of beneficial agent.

BACKGROUND ART Over the past decade, much research has been devoted to developing new and useful devices for delivering beneficial agents to agent receptor environments of use. The traditional manner of administering sustained parenteral treatments is an intravenous drip. While this may be perfectly acceptable in a hospital environment, it obviously imposes severe restrictions on the activity of the recipient. As a result, considerable research over the last few years has been devoted to the development of small portable infusion pumps.

A range of devices has appeared, including those with electric motors that drive pumps, and others powered by the elastic tension of an inflated balloon. While these delivery techniques are being used, they have certain disadvantages. For example, the use of electromechanical pumps is expensive and sometimes inconvenient because of their size and weight.

An alternative approach is to drive the infusor osmotically with a liquid or gaseous fluid. In comparison with mechanically driven devices, osmotic pumps are small, reliable, uncomplicated and inexpensive to manufacture. United States Patent No. 3,604,417 discloses a pump in which a moveable piston separates the drug and salt chamber, and both the drug and salt chamber are loaded into the pump as solutions. United States Patent No. 4,474,048 discloses another modification employing an impermeable elastic wall, and a moveable end wall which can be screwed into the pump to deliver a pulse dose of the contained drug at any time during operation of the pump. United States Patent No. 4,474,575 discloses a similar pump where the flow rate of the dispensed drug can be varied by altering the area of semipermeable membrane exposed to the water chamber. United States Patent No. 4,552,561 discloses a pump assembly for use with a small osmotic pump, which can be filled in advance of use with the active agent to be dispensed. The action of the pump is initiated by filling the lower chamber of the housing with a hydrogel . Once the pump is in action, an optional mechanism for delivering pulse doses can be employed.

In United States Patent No. 3,760,984, there is disclosed an osmotic delivery device comprising an inner collapsible container carrying on its outer surface a layer of an osmotic solute and a surrounding layer of a polymer permeable to fluid and impermeable to solute. In United States Patent No. 3,971,376, a device is disclosed comprising a capsule having a unitary wall formed of a substantially noncollapsible elastic material that maintains a constant volume and which is adapted to be implanted subcutaneously. A textile fabric may be imbedded in the capsule wall. The fabric strengthens the wall and acts as a reinforcement. In United States Patent No. 3,987,790, there is disclosed another osmotic delivery device which contains an outer shape-retaining membrane which is sufficiently rigid to be substantially undeformed by the hydrostatic pressure exerted by water permeating through the membrane.

United States Patent No. 3,995,631, discloses a device (Figure 4 in the Patent) comprising an inner flexible bag containing a drug formulation. The bag separates the drug from an osmotically effective solute material. Both the drug and the solute are contained within a housing having an exterior wall that is, at least in part, semipermeable. United States Patent No. 3,995,632 discloses a similar device which incorporates a movable barrier within the housing. The barrier divides the housing into two compartments, one containing the solute and the other containing the drug. The solute- containing compartment has an exterior wall that is, at least in part, semipermeable. This compartment acts as an osmotic driver for the device. United States Patent No. 4,410,328 discloses an osmotically driven syringe/pump device. The osmotic driver in this device is in the form of a tablet comprising an osmotically effective solute, such as sodium chloride, within a semipermeable wall having a single exit orifice drilled therethrough. United States Patent No. 4,968,884 discloses an osmotic engine and an osmotically driven dispensing device. The device includes a syringe having a movable piston, the piston dividing the syringe into a beneficial agent compartment and a driving compartment. The device also contains a fluid reservoir and osmotic engine intermediate the reservoir and the driving compartment of the syringe.

United -States Patent No. 4,898,582 describes a device having two side-by-side compartments, the first containing the drug and an osmotic pump, and the second containing the driving liquid for the pump. The two chambers are separated by a barrier that is ruptured to activate the osmotic pump.

United States Patent No. 4,838,862 describes a device having a rigid housing containing a reservoir; an osmotic pump; a foil seal separating the reservoir and pump; a drug reservoir separated from the osmotic pump by an impermeable elastic diaphragm; and an activating device that ruptures the foil seal and initiates the osmotic action of the device.

While the above-described devices are useful for delivering many agents, and while they represent a valuable contribution to the delivery art, there has been a need in the art for a fluid driven dispensing device that is light in weight. Unfortunately, all the fluid driven dispensing devices utilized in the prior art have required a one to one ratio of driving fluid volume to beneficial agent volume to operate. Thus, if a prior art device is to deliver 50 ml of beneficial agent, the device needed at least 50 ml of driving fluid to operate. Accordingly, the prior art devices are particularly heavy in weight when delivering large volumes of beneficial agent. Moreover, given the proximity of the driving fluid and beneficial agent in the prior art devices, any leakage of driving fluid could easily result in contamination of the beneficial agent. Those skilled in the art will recognize that if a fluid driven dispensing device can be provided that is essentially free from the above tribulations, such a device would be a valuable advancement in the art and a useful improvement. SUMMARY OF THE INVENTION The present invention provides a fluid driven dispensing device for delivering a beneficial agent to an environment of use. The device comprises a housing means, a piston means slidably received within the housing means, the piston means having first and second ends, the first end having a cross-sectional area greater than the second end, a beneficial agent compartment formed between the housing means and the first end of the piston means, a driving compartment formed between the housing means and the second end of the piston means, and an engine retaining means for maintaining an engine means adjacent the driving compartment, which engine means is actuatable by a fluid; whereby a given volume of fluid delivered to the driving compartment from the engine means will dispense a larger volume from the beneficial agent compartment. The difference in cross-sectional area between the first end of the piston means and the second end of the piston means causes an amplification effect, such that a given volume of driving fluid delivers a greater volume of beneficial agent. The weight advantage such an amplification provides can be seen in Figure 1. Preferably, the area of the first end of the piston means is at least 1.5 times greater than the area of said second end of the piston means. Most preferably, the area of said first end is between 3 and 10 times greater than the area of said second end. The cross-sectional area referred to herewithin is the area defined by the cross-section of arrow 2-2 in Figure 2.

Preferably, the first end of the piston means comprises a plunger means and the second end of the piston means comprises a piston, wherein the ratio of the cross-sectional area of the plunger means to the opposite end or second end of the piston is at least 1.5 to 1, more preferably the ratio of the cross-sectional area of the plunger means to the opposite end of the piston is between 3 and 10 to 1.

The invention also provides a safety mechanism for ensuring that the driving fluid does not contaminate the beneficial agent. The safety advantage of this invention results from the separation of the driving compartment and the beneficial agent compartment by the piston means, thus minimizing the possibility of leakage between the driving compartment and the beneficial agent compartment. Preferably, a sealing means provides a fluid tight seal between the piston means and the driving compartment.

The engine means of the invention is an osmotic engine. The reservoir fluid to drive the osmotic engine can be either 1) added to a reservoir compartment adjacent the osmotic engine, 2) released from a sealed container into the reservoir compartment by a releasing means, 3) released from a sealed portion of the reservoir compartment by an releasing means, or 4) absorbed from the environment of use. The reservoir fluid is then imbibed into the osmotic engine forming a driving fluid. The driving fluid is delivered by the osmotic engine into the driving compartment. The driving fluid can be a liquid or a gas. The osmotic engine comprises an osmotic solute, a wall portion permeable to the fluid disposed between the solute and the reservoir means, and an outlet means in fluid communicating relationship to the driving compartment.

In operation, a beneficial agent is delivered from the device in the following manner. Driving fluid, either liquid or gaseous, is pumped into the driving compartment by the osmotic engine. Initially, the driving compartment has a small volume. The delivered fluid exerts pressure on the second end of the piston means, the piston means moves within the housing, increasing the volume of the driving compartment. The movement simultaneously decreases the volume of the beneficial agent compartment, forcing the beneficial agent from the compartment and delivering it to the environment of use.

The device of the invention can further comprise an overflow reservoir and a valve means disposed in fluid communicating relationship to the driving compartment and the overflow reservoir, the valve means being movable from a closed position to an open position permitting fluid flow from the driving compartment to the overflow reservoir. Preferably, the overflow reservoir is within the housing means and surrounds at least a portion of the piston means. The reservoir means of the device can comprise collapsible enclosure means enclosing the reservoir fluid for the osmotic engine, the enclosure means being disposed within the driving housing. Releasing means for releasing the reservoir fluid from the enclosure means can also be disposed within the driving housing; by which the reservoir fluid may be released into contact with the osmotic engine.

The device can further comprise vent means for the driving housing to permit air to enter the driving housing and permit collapse of the enclosure means. Optionally, the releasing means can provide a fluid flow path for the reservoir fluid between the driving housing and the osmotic engine.

In the preferred embodiment, the fluid driven dispensing device for delivering the beneficial agent to an environment of use comprises a syringe housing adapted to contain the beneficial agent and having outlet means proximate one end thereof, an amplification housing attached at one end to the other end of the syringe housing, a driving housing adapted to contain a reservoir means and attached to the other end of the amplification housing, a piston means slidably received within the syringe housing and the amplification housing, the end of the piston means within the syringe housing having a larger cross-sectional area than the end of the piston means within the amplification housing, the piston means being movable from a first position proximate the amplification housing end of the syringe housing to a second position proximate the outlet means, and means for retaining an engine in fluid communicating relationship with both the reservoir means and the piston means; whereby a given volume of fluid delivered to said piston means from said engine means will dispense a larger volume from said syringe housing.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows the effect beneficial agent volume has on the approximate weight of a fluid driven dispensing device at different amplification ratios.

FIG. 2 is a cross-sectional view of a fluid driven dispensing device of the present invention.

FIG. 3 is a cross-sectional view of another embodiment of a fluid driven dispensing device of the present invention.

FIG. 4 is a cross-sectional view of another embodiment of a fluid driven dispensing device of the present invention. FIG. 5 is a cross-sectional view of another embodiment of a fluid driven dispensing device of the present invention. FIGS. 6(a) and 6(b) are cross-sectional views of a reservoir compartment of the present invention shown in a pre-activated position and in a post-activated position.

FIGS. 7(a) and 7(b) are cross-sectional views of a reservoir compartment of the present invention shown in a pre-activated position and in a post-activated position.

FIG. 8 is a cross-sectional view of another embodiment of a fluid driven dispensing device of the present invention.

FIG. 9 is a cross-sectional view of another embodiment of a fluid driven dispensing device of the present invention.

FIGS. 10(a), 10(b) and 10(c) are cross-sectional views of another embodiment of a fluid driven dispensing device of the present invention.

FIG. 11 is a cross-sectional view of another embodiment of a fluid driven dispensing device of the present invention.

MODES FOR CARRYING OUT THE INVENTION Figure 2 is an opened, sectional view of a fluid driven dispensing device depicting its internal structure. In Figure 2, a device 10 comprises a housing 12 containing a movable plunger 26 disposed in contacting arrangement with one end of a moveable piston 14. In another embodiment of this invention, plunger 26 and piston 14 can be releasably attached or fixedly attached. Housing 12 comprises three separate sub-housings, a syringe housing 16, an amplification housing 18 and a driving housing 20. Internal surface 28 of syringe housing 16 and plunger 26 define a beneficial agent compartment 30. Plunger 26 fits snugly against internal surface 28 of syringe housing 16 and is slidably movable along the internal surface 28, such that the volume of beneficial agent compartment 30 changes as plunger 26 moves. Agent compartment 30 has a delivery port 32 that can be shaped to accept a hypodermic needle, an IV catheter, or the like. Port 32 can also be adapted to accept a uer plug that is removed prior to connection with a hypodermic needle or IV catheter.

Syringe housing 16 is adapted to be fixedly attached to amplification housing 18 with a suitable fastening means 22, such as screw threads. Internal surface 29 of amplification housing 18 surrounds piston 14. Plunger 26 is disposed in contacting arrangement with the one end of piston 14. Piston 14 is slidably movable along internal surface 29 of amplification housing 18. The cross-sectional area of piston 14 is smaller than the cross-sectional area of plunger 26.

Piston 14 comprises a rod 24 and a seal 36. Seal 36 on rod 24 provides a fluid tight seal between seal 36 and the internal surface 29 of amplification housing 18. Preferably, the amount of friction between internal surface 29 and rod 24 is kept at a minimum. An osmotic engine 38, the internal surface 29 of amplification housing 18, seal 36 and the end of piston 14 define a driving compartment 40. The volume of driving compartment 40 changes as piston 14 moves. Optionally, the piston can be telescoping, such that an inner piston telescopes from an outer piston; This can be used to shorten the length of the device.

In this embodiment, the osmotic engine 38 includes a shaped wall defining an interior compartment. The interior compartment contains an osmotically effective solute. At least a portion of the wall is comprised of a material that is permeable to and hydrated by an external fluid. The wall material is sufficiently impermeable to the solute to generate an osmotic pressure differential across the wall after the wall is exposed to an external fluid. The wall also has a passageway 41 therethrough connecting the osmotic solute- containing compartment with the driving compartment. Amplification housing 18 is adapted to be fixedly attached to driving housing 20. In this regard, amplification housing 18 and driving housing 20 are provided with suitable fastening means 42, such as screw threads. As shown in Figure 2, driving housing 20 is provided with an annular shoulder 44. When driving housing 20 is attached to amplification housing 18, osmotic engine 38 is tightly compressed between annular shoulder 44 on driving housing 20 and an annular shoulder 46 on amplification housing 18. Preferably, shoulders 44 and 46 provide a fluid tight seal with osmotic engine 38, where sealing means 50 and 52 are compressed tightly between the annular shoulders 44, 46 and osmotic engine 38.

Alternatively, the sealing means could be incorporated in the osmotic engine. Osmotic engine 38 is oriented so that driving fluid is pumped or generated into driving compartment 40.

The internal surface 31 of driving housing 20 and osmotic engine 38 define a reservoir compartment 54. Fluid is added to reservoir compartment 54 through port 56. Ambient pressure is maintained on the fluid in the reservoir 54 by means of a vent 58. The vent can be a one-way valve or can be made from a material that is permeable to air but not permeable to the fluid. Preferably, the vent is a hydrophobic, air-permeable material, such as porous teflon. Optionally, reservoir compartment 54 can contain a loose fluid absorbent material 60. Material 60 expands to fill up reservoir 54, when wetted, so as to maintain osmotic engine 38 continuously wet after the fluid is delivered to reservoir compartment 54, regardless of the movement or physical orientation of the device. Figure 3 depicts another embodiment of a fluid driven dispensing device. This embodiment is the same as described in Figure 2, except for the features hereafter described. In this embodiment, housing 12 is one continuous housing and is not separable into three different sub-housings. Piston 14 and plunger 26 are provided with suitable fastening means 34, such as snap connects. Rod 24 and seal 36 are provided with suitable fastening means 62, such as snap connects.

Osmotic engine 38 is tightly compressed between annular shoulder 46 and a wick retaining means 64. Preferably, the wick retaining means 64 and annular shoulder 46 provide a fluid tight seal with osmotic engine 38, where sealing means 52 is compressed tightly between osmotic engine 38 and wick retaining means 64.

Reservoir compartment 54 is defined by internal surface 31 of housing 12 and wick retaining means 64. Wick retaining means 64 maintains fluid absorbent material 60 in contact with osmotic engine 38. Fluid absorbent material 60 can be an absorbent grade cotton, a knit material, a cellulose sponge or any suitable absorbent material.

Figure 4 is another embodiment of a fluid driven dispensing device. This embodiment is the same as described in Figure 3, except for the features hereafter described. In this embodiment, housing 12 comprises syringe housing 16, amplification housing 18 and driving housing 20. Amplification housing 18 is adapted to be fixedly attached to syringe housing 16 with suitable fastening means 22, such as quick connects. Driving housing 20 is adapted to be movably attached to amplification housing 18. In this regard, driving housing 20 and amplification housing 18 are provided with suitable fastening means 66, such as snap connects that permit rotation between a first and second position.

Reservoir compartment 54 is defined by a retention cap 68, driving housing 20 and wick retaining means 64. Reservoir compartment 54 contains a releasing means 70 that operates to puncture or rupture a fluid-filled container 72 located inside reservoir compartment 54. Container 72 includes any rigid or non- rigid container that is impermeable to the reservoir fluid and can be ruptured or opened by the releasing means. Preferably, container 72 is a polymeric composition, such as high or low density polyethylene. The releasing means includes any means to open the barrier of the sealed container.

Retention cap 68 is adapted to be fixedly attached to driving housing 20 with suitable fastening means 74, such as snap connects. In operation, retention cap 68 is removed, container 72 is placed in reservoir compartment 54. Retention cap 68 is then attached to driving housing 18. Pressure is applied to a button 69 on retention cap 68 forcing releasing means 70 against container 72. Container 72 then releases fluid into reservoir compartment 54 where it is absorbed by material 60. Releasing means 70 can be located anywhere in reservoir compartment 54. Preferably, it is located adjacent to osmotic engine 38 or adjacent to retention cap 68. Osmotic engine 38 imbibes reservoir fluid from material 60 and pumps driving fluid into driving compartment 40. A valve 76 interconnects driving compartment 40 and an overflow reservoir 78. Overflow reservoir 78 is defined by amplification housing 18 and surrounds piston 14. Valve 76 can be opened and closed when driving housing 20 is moved between a first position and second position. In the first or closed position, the driving fluid is pumped into driving compartment 40. In the second or open position, the driving fluid is pumped into overflow reservoir 78. The opening and closing of valve 76 allows the delivery of beneficial agent to be stopped or interrupted at any time and to be restarted again, as long as the osmotic engine can deliver driving fluid. A vent 79 is located on overflow reservoir 78. If the driving fluid is a liquid, then the vent is made from a material that is permeable to air, but not permeable to the driving fluid. Vent 79 permits air to leave overflow reservoir 78 as fluid enters it. If the driving fluid is a gas then vent 79 is a one way valve that permit gas to leave overflow reservoir 78, but not to enter overflow reservoir 78. Figure 5 represents another embodiment of the fluid driven dispensing device. This embodiment is the same as Figure 4, except for the features hereafter described. In this embodiment, housing 12 is comprised of amplification housing 18 and syringe housing 16. Amplification housing 18 is adapted to be fixedly attached to syringe housing 16. In this regard, amplification housing 18 and syringe housing 16 are provided with suitable fastening means 22, such as snap connects.

A reservoir compartment 54 is defined by amplification housing 18 and surrounds piston 14. Reservoir fluid in reservoir compartment 54 communicates with osmotic engine 38 by wieking channel 80. Amplification housing 18 moves a valve 81 between a first or opened position where reservoir fluid communicates with osmotic engine 38 by wicking channel 80 and second or closed position where the reservoir fluid in reservoir compartment 54 is blocked from communicating with osmotic engine 38. Figures 6(a) and 6(b) represent embodiments of the reservoir compartment of the fluid driven dispensing device. This embodiment is the same as Figure 2, except for the reservoir compartment. Figure 6(a) represents the reservoir compartment prior to activation. Figure 6(b) represents an activated reservoir compartment. The reservoir compartment 54 comprises a storage reservoir 82 and a use reservoir 84. The storage reservoir is defined by driving housing 20 and a breakable barrier 86. Preferably, the breakable barrier is a thin foil seal or polymeric diaphragm. The use reservoir is defined by a collapsible surface 88, releasing means 70 and osmotic engine 38. Collapsible surface 88 includes any surface that can expand and contract in volume, such as a diaphragm, bellows, a bag and the like. Storage reservoir 82 and use reservoir 84 communicate by a releasing means 70.

Retention cap 68 is movably affixed to driving housing 20, by suitable fastening means 74, such as screw connects. When retention cap 68 is rotated, releasing means 70 ruptures barrier 86 and fluid in storage reservoir 82 moves through releasing means 70 to use reservoir 84. As the volume of storage reservoir 82 decreases, the volume of fluid in use reservoir 84 increases, causing collapsible surface 88 to expand. As the engine consumes the fluid in use reservoir 84, collapsible surface 88 contracts to decrease the volume of use reservoir 84. Ambient pressure is maintained external to collapsible surface 88 by a vent 92. A support 94 reinforces the structure of osmotic engine 38 enabling it to withstand the forces generated by the operation of the device. Figures 7(a) and 7(b) represent another embodiment of the reservoir compartment of the fluid driven dispensing device. This embodiment is the same as Figure 2, except for the reservoir compartment. Figure 7(a) represents the reservoir compartment prior to activation. Figure 7(b) represents an activated reservoir compartment.

The reservoir compartment 54 comprises a collapsible surface 88 and a breakable barrier 86. Between osmotic engine 38 and breakable barrier 86 is releasing means 70.

Retention cap 68 is movably affixed to driving housing 20, by suitable fastening means 74, such as screw connects. When retention cap 68 is rotated, releasing means 70 ruptures barrier 86. Fluid from reservoir compartment 54 flows through releasing means 70 into osmotic engine 38. As the engine consumes the fluid in reservoir compartment 54, collapsible surface 88 contracts. Ambient pressure is maintained on collapsible surface 88 by a vent 92. A support 94 reinforces the structure of osmotic engine 38 enabling it to withstand the forces generated by the operation of the device.

Figure 8 represents another embodiment of the fluid driven dispensing device. This embodiment is the same as Figure 2, except for the features hereafter described. In this embodiment, an osmotic engine 38, the internal surface 29 of amplification housing 18, seal 36 and the end of piston 14 define a driving compartment 40. The volume of driving compartment 40 changes as piston 14 moves. The osmotic engine 38 is oriented so that driving fluid is pumped into driving compartment 40.

The internal surface 31 of housing 12 defines a reservoir compartment 54 that surrounds osmotic engine 38 and piston 14. Fluid is added to reservoir compartment 54 through port 56. Ambient pressure is maintained on the fluid in the reservoir 54 by means of a vent 58.

Figure 9 represents the presently preferred embodiment of the fluid driven dispensing device. This embodiment is the same as Figure 2, except for the features hereafter discussed. Syringe housing 16 is adapted to be movably attached to amplification housing 18 with a suitable fastening means 22, such as locking screw threads. When amplification housing 18 is attached to syringe housing 16, amplification housing 18 can be twisted to move piston 14 into contact with plunger 26. Further twisting decreases the volume of beneficial agent compartment 30 as plunger 26 moves, expelling any air trapped in beneficial agent compartment 30 when port 32 is pointed generally in an upward direction. A locking mechanism 49 can be employed to prevent amplification housing 18 from being further twisted after all trapped air has been removed.

As shown in Figure 9, when driving housing 20 is attached to amplification housing 18, osmotic engine 38 is tightly compressed between annular shoulder 46 on driving housing 20 and releasing means 70. Preferably, shoulder 46 and releasing means 70 provide a fluid tight seal with osmotic engine 38, where sealing means 50 is compressed tightly between the annular shoulder 46, releasing means 70 and osmotic engine 38. Alternatively, the sealing means could be incorporated in the osmotic engine. The reservoir compartment 54 comprises a collapsible surface 88, preferably a bellows-shaped surface, and a breakable barrier 86. Between osmotic engine 38 and breakable barrier 86 is releasing means 70. -Retention cap 68 is fixedly affixed to driving housing 20, by suitable fastening means 74, such snap connects. In operation, a protective cap 55 is removed and button 69 on retention cap 68 is pressed, forcing releasing means 70 to rupture barrier 86. Preferably releasing means 70 is an angled blade mounted on a support. In this manner, releasing means 70 also reinforces the structure of osmotic engine 38. Fluid from reservoir compartment 54 flows through releasing means 70 into driving engine 38. As the driving engine consumes the fluid in reservoir compartment 54, collapsible surface 88 contracts. Ambient pressure is maintained on collapsible surface 88 by a vent 92. The vent can be a one-way valve or can be made from a material that is permeable to air but not permeable to the fluid. Preferably, the vent is a hydrophobic, air- permeable material, such as porous teflon. Figure 10(a), 10(b) and 10(c) is another embodiment of a fluid driven dispensing device. This embodiment is the same as described in Figure 2, except for the features hereafter described. In Figure 10(a), the internal surface 31 of driving housing 20, osmotic engine 38, releasing means 75 and hydration plunger 77 define a reservoir compartment 54. Releasing means 75 provides a seal between reservoir compartment 54 and osmotic engine 38.

Figure 10(b) represents an activated reservoir compartment. To activate the reservoir, releasing means 75 is pulled outwardly from the driving housing 20. Figure 10(c) represents a reservoir compartment after approximately half the reservoir fluid has been pumped by the osmotic engine 38. As reservoir fluid is absorbed by the osmotic engine 38, hydration plunger 77 and releasing means 75 move inwardly towards the osmotic engine 38, thereby decreasing the volume of reservoir compartment 54. Figure 11 is another embodiment of a fluid driven dispensing device. This embodiment is the same as described in Figure 2, except for the features hereafter described. In this embodiment, the internal surface 31 of driving housing 20, osmotic engine 38, releasing means 75 and hydration plunger 77 define a reservoir compartment 54. Releasing means 75 provides a seal between reservoir compartment 54 and osmotic engine 38. To activate the reservoir, button 69 is depressed. Button 69 releases spring 71, which pulls releasing means 75 outward from the driving housing 20. Reservoir fluid then contacts osmotic engine 38. As reservoir fluid is absorbed by the osmotic engine 38, hydration plunger 77 and releasing means 75 move inwardly towards the osmotic engine 38, thereby decreasing the volume of reservoir compartment 54. In operation, beneficial agent compartment 30 may be prefilled with a liquid dose of beneficial agent, or may be filled by the patient using a retracting device (not shown) which can be easily connected to plunger 26 for drawing the dose and which is easily disconnected from plunger 26 once the appropriate dose has been drawn.

The distal end of piston 14 is positioned immediately adjacent driving engine 38 in order to minimize the initial volume of driving compartment 40 and thereby minimize the time required to initially fill driving compartment 40. The imbibition of fluid from reservoir 54 into engine 38 is caused by an osmotic imbalance between the fluid and the composition of osmotic agent. The rate of fluid influx per unit area of semipermeable membrane will depend upon the composition and thickness of the membrane and the magnitude of the osmotic imbalance.

In devices that are used to administer a drug intravenously, the osmotic pressure of the solute solution must exceed the patient's blood pressure. Sodium chloride is an especially effective osmotic solute in that the osmotic pressure of sodium chloride is sufficiently high to remove the dependence of pumping rate on the osmotic pressure of the surrounding environment. By keeping the osmotic imbalance substantially constant, the influx of fluid into engine 38 will be constant and so will both: (1) the rate of delivery of driving fluid from engine 38 into driving compartment 40, and (2) the rate of injection of the beneficial agent from agent compartment 30. Such operation is called "steady state" or "tonic" operation and is characterized by a controlled constant rate of injection at predetermined baseline level. A wide range of appropriate solutes for use in osmotic pumps are disclosed in United States Patent No. 4,969,884, which is incorporated by reference. The engine can use a solute in the solid or liquid phase. Additionally, the term "solute" includes hydrogels that absorbs fluid imbibed into the engine, and can expand from a rested to an expanded state. A wide range of appropriate hydrogels for use in osmotic pumps are disclosed in United States Patents Nos. 4,327,725 and 4,783,337, which are incorporated by reference. The osmotic engine can also primed by wetting the engine and filling the void space in the osmotic component, as disclosed in U.S. Patent No. 5,223,266, which is incorporated herein by reference. By priming the osmotic engine, the start-up time for drug delivery to begin is shortened.

The solute in an osmotic engine can also contain a gas generating composition. The semipermeable membrane surrounding the osmotic engine is substantially impermeable to the passage of gas generating composition, has a low permeability to the passage of an internally created gas and is substantially permeable to the passage of the reservoir fluid. In operation, reservoir fluid is imbibed through the membrane to continuously wet and dissolve the gas generating composition, causing it to react and produce a large volume of gas. This gas expands and passes into driving compartment 40. This action correspondingly causes pressure to be exerted on the piston 15 which thereby pushes this and the plunger 26, forcing beneficial agent into the environment of use through port 32. Preferably, a gas generating osmotic engine is used when it is desired to deliver beneficial agent is less than 24 hours, more preferably, in less than 10 hours.

The gas generating composition comprises a dry compound or anhydrous mixture of compounds that when intimately contacted by the reservoir fluid, generates a gas that exerts a pressure to drive the dispensing system. The composition comprises a preferably solid acidic material, and a preferably solid basic material that dissolve and react in the presence of reservoir fluid that enters the engine 38. The composition may be in powder, crystalline, granular or layered form. Alternately, the gas generating composition may be present homogeneously or heterogeneously dispersed within a matrix. The matrix is a polymer permeable to the passage of reservoir fluid and permeable to the passage of the generated gas. The rate of gas generated in this embodiment is governed by the rate of passage of fluid through the polymer and the rate of passage of fluid through the membrane. The acids that can be used include organic acids such as malic, fumaric, tartaric, itaconic, aleic, citric, adipic, succinic and mesaconic, and the corresponding anhydride such as itaconic anhydride, citriconic anhydride. Also inorganic acids such as sulfamic or phosphoric, and the like can be used for gas generation. Acid salts such as the salts of organic foods can be used including monosodium citrate, potassium acid tartrate and potassium bitartrate. The basic compounds include metal carbonate and bicarbonate salts, such as alkali metal carbonates and bicarbonates, or alkaline earth carbonates and bicarbonates. Exemplary materials include the alkali metals lithium, sodium, potassium carbonate and bicarbonate, and the alkaline earth compounds magnesium and calcium carbonate or bicarbonate. Also useful are ammonium carbonate, ammonium bicarbonate and ammonium sesquecarbonate.

The combination of certain of these acids and bases results in a more rapid gas production when contacted with water. In particular, either citric acid or a mixture of citric acid and tartaric acid and sodium bicarbonate give a rapid gaseous reaction that can be used. It will be understood the amount of acidic and basic materials in a couple can vary over a wide range to satisfy the amount of gas generation needed to dispense beneficial agent from dispenser 10. The essentially dry or anhydrous couple is preferably substantially stoichiometrically balanced to produce a combination that generates carbon dioxide. Also, the acid and base materials can be used in any convenient proportion between 1 to 200 parts and 200 to 1 part on a weight basis to produce the desired results. In addition, the gas generating material can be a substance that generates gas on contact with water such as calcium carbide or carbure.

The gas generating composition can also contain a foaming agent, such as a surfactant, having suitable foaming properties to stabilize the gas generated. The surfactant when mixed with the imbibed reservoir fluid and the gas produced by the gas generation composition, forms a foam. The surfactant can be cationic, anionic or nonionic. Exemplary cationic surfactants include, 1auryldimethylbenzyl mmoniurn chloride p-diisobutylphenoxyethoxyethyl- dimethylbenzylammonium chloride, alkyldimethylbenzylammoniurn chloride, laurylisoquinolinium bromide, cetylethyldimethylammoniurn bromide, stearyl-dimethylbenzylammoniurn chloride, N-soya-N-ethyl- morpholinium-ethosulphate, N(acyl-colamino-formyl- methyl )pyridiniurn chloride, a mixture comprising alkyl (C₉H_1g to C₁₅H₃₁) tolylmethyltrimethylammoniurn chloride and lauryl-isoquinolinium bromide, coco-amidoalkyl betaine, and N-lauryl-myristyl-0-aminopropi- onic acid. Exemplary anionic surfactants include linear alkylaryl sulfonates prepared by Friedel-Crafts reaction of an olefin and benzene wherein the olefin has from 10 to 18 carbon atoms, and the alkali metal salts thereof, and other anionic surfactants such as alkylaryl sulphonate, capryl i idazoline derivatives, dioctylester of sodium sulphosuccinic acid, sodium lauryl sulfate, sodium salt of alkylated aryl polyether sulphate, triethanolamine salt of lauryl sulphate, triethanolamine salt of alkylaryl sulfonate, and mixtures thereof. Exemplary nonionic surfactants include alkylated aryl polyether alcohol, polyethylene glycol tertdodecyl thioether, fatty acid amide condensates, aromatic polyglycol ether condensates, secondary amide of 1auric acid, fatty acid alkanolamine condensates, sorbitan monolaurate, sorbitan monolaurate polyoxyethylene, sorbitan mono-oleate, sorbitan mono-oleate polyoxyethylene derivative, mannide mono-oleate polyoxyethylene lauryl ether, polyoxyethylene esters of mixed resins and fatty acids, and mixtures thereof, and surfactants generically including the condensation product of a linear aliphatic alcohol having from 8 to 22 carbon atoms in its aliphatic portion and an alkylene oxide wherein the oxide constitutes from about 55% to 80% by weight of the surfactant molecule. The amount of surface active agent used is an amount sufficient to achieve the intended result, normally, the amount will range from 0.01% to about 15% by weight, based on the total weight of all the compounds in the osmotic engine. The surface active agents are commercially available and they are also known in Solubilization By Surface-Active Agents, by Elworthy, P.H., et al , 1968, published by Chapman and Hall Ltd., London; Systemic Analysis of Surface-Active Agents, by Rosen, Milton J., et al, 1972, published by Wiley-Interscience Inc., Sydney; Encyclopedia of Polymer Science and Technology, Vol. 13, pages 477 to 486, 1970, published by John Wiley & Sons Inc., New York; and United States Patent Nos. 2,674,619, 3,340,309, 3,504,041, and 3,796,817. Suitable foam forming agents which can be mixed with the gas generating composition for the above described purpose include those that produce a foam that is stable within a wide range of tempera¬ ture, that produces a foam that does not collapse in the presence of other compounds, and produces a foam that is pharmaceutically accept¬ able when the syringe dispenses a drug to an animal. Exemplary foam-formers are alkyl aryl sulphonates, sodium, ammonium and alkanolamine ether sulphates such as monoethanolamine lauryl ether sulphate and dodecyl benzene sulphonate, a mixture consisting of lauryl-amidopropyl-N-dimethylamino acetic acid and stearylamido- propyl-N-dimethylamino acetic acid, a mixture consisting of mono¬ ethanolamine lauryl ether sulphate and methyl cellulose in a weight ratio of 3:1, a foaming surfactant consisting of sodium alkyl benzene sulphonate in combination with lauryl sulphate and sodium lauryl sulphoacetate. The amount of foam-forming agent used usually is about 0.01% to 15% by weight based on the total weight of the com¬ pounds in the device. Representative foam-formers and foam systems are described in The Theory and Practice of Industrial Pharmacy, by Lachman, L. et al , pages 618 to 621, 1970, published by Lea & Febiger, Philadelphia; and in Cosmeticology. by Harry, R.G., pages 243 to 250, 1973, published by Chemical Publishing Co. Inc., New York.

In those embodiments of the osmotic engine which utilize a gas generating composition, at least a portion of the driving fluid produced by engine 38 for driving piston 15 is a gas. In determining the amount of gas generating composition needed within engine, the compressibility of the gas produced by the gas generating reaction must be taken into account. In a typical syringe, the pressures generated within driving compartment will be such that the volume of gas produced will be on the order of about 30% to 70% of the volume of the gas at standard atmospheric pressure. Those skilled in the art will appreciate that the compressibility of the gas produced is simply compensated for by adding from 70% to 30% more gas generating composition than would be required at standard atmospheric pressure. The osmotic engine should have good strength and good shape- retaining characteristics even after the engine has delivered part of its osmotic charge. In particular, the osmotic engine might have a rigid reinforcing structure or support, either internal or external, to enable the engine to substantially retain its original shape during use and enabling the engine to withstand the stresses imposed by fixedly securing the engine within an osmotically driven dispensing device, without comprising the operation of the device. The support can be any suitable means to provide rigidity and strength to the semipermeable membrane, such as a ring-shaped member and/or a screen. The support can be made of ceramic, metal, plastic or the like. Alternatively, a composite membrane comprising a semipermeable membrane and a microporous membrane can be used to impart strength and rigidity. Preferably, the osmotic engine described in United States Patent No. 4,969,884, which is incorporated by reference, along with a screen support is used.

The fluid driven dispensing devices of the present invention may be used to deliver dosages having a fluid volume in a range of about 0.5 ml to about 200 ml over a period of about 0.1 to about 7 days. The engines useful in the fluid driven dispensing devices disclosed herein typically provide a delivery rate of about 0.1 to about 50 ml/day. The fluid driven dispensing device can optionally be made as a reusable device. That is the agent compartment can be refilled, the engine can be replaced, with another engine having the same or different pumping rate, and the reservoir can be refilled with reservoir fluid or pre-packaged reservoir fluid. The housing for the device may be manufactured by injection or compression molding, vacuum forming or any standard technique for handling thermoplastic polymers, such as polyvinyl chloride, polymethylmethacrylate, polyethylene, polycarbonate, polysulfone or the like. Alternatively, the housing could be made from thin sheets of stainless steel, aluminum or like metal.

The assembled fluid driven dispensing device is placed on the skin with a needle (not shown) penetrating the cutaneous layer and lying substantially flush against the skin. Alternatively, the needle can be inserted into a vein and the syringe utilized as an IV infusion device. When the fluid driven syringe is used in combination with a subcutaneous or IV needle, the needle is preferably composed of stainless steel and has a gauge in the range of 25 to 30.

Alternatively, the fluid in compartment 54 may be inert and the device may be used simply as a displacement pump. In this alternative, the device will have to be suitably interconnected by well known means to a reservoir of a fluid beneficial agent to be discharged, such that the inert fluid displaces the beneficial agent from the reservoir in a predetermined regimen to the desired administration site. The present invention can either be filled when its use is desired or can be filled and stored for extended periods of time and then activated on demand. Accordingly, a reservoir fluid is introduced into reservoir compartment 54 either 1) added to a reservoir compartment adjacent the osmotic engine, 2) released from a sealed container into the reservoir compartment by a releasing means, 3) released from a sealed portion of the reservoir compartment by a releasing means, or 4) absorbed from the environment of use. The releasing means may be a simple needle, a plurality of needles, a serrated support, a cutting blade and the like to tear or rip a sealed container or it may be a moving partition, such as lever, a gate, a plunger, a plug and the like to open a sealed container. It is intended that the scope of the present invention should encompass any releasing means.

If the reservoir means is a separate compartment, it should be completely impermeable to the fluid in the reservoir, otherwise slow migration of the fluid from the reservoir will cause the device to deteriorate during storage. If the reservoir means requires elastomeric properties, materials known in the art, include barrier coated latex rubber, polyisoprene, butyl rubber, nitrile rubber, copolymers of styrene/butadiene, high and low density polyethylene, polyester resins, polyvinyldiene chloride, teflon and the like. These elastomers can be faced with a thin layer of aluminum or other metal. Alternatively, the surface can be made of high density polyethylene, polyvinyl chloride, acrylonitrile, stainless steel, aluminum or a like metal, or thermoplastic polymers, such as polyvinyl chloride, polymethylmethacrylate, polyethylene, polycarbonate, polysulfone, and the like. Preferably, the reservoir fluid is sterile water but other liquids could also be used. The driving fluid is pumped from the driving engine into driving compartment 40. Thereafter, the pumping of solution from engine 38 causes rod 24 to move plunger 26 toward delivery port 32, thereby forcing the beneficial agent out of the port.

The term "beneficial agent", as used herein, includes any agent or compound, that can be delivered from the device to produce a beneficial and useful result, including any physiologically (i.e., denotes the administration of a beneficial agent to produce normal levels or functions) or pharmacologically active substance (i.e, denotes variations in response to amount of beneficial agent administered to host) that produces a local or systemic effect when administered to an animal. In general, this includes beneficial agents in all of the major therapeutic areas including, but not limited to: ACE inhibitors, adenohypophyseal hormones, adrenergic neuron blocking agents, adrenocortical steroids, inhibitors of the biosynthesis of adrenocortical steroids, alpha-adrenergic agonists, alpha-adrenergic antagonists, selective alpha-two-adrenergic agonists, analgesics, antipyretics and anti-inflammatory agents, androgens, local anesthetics, general anesthetics, antiaddictive agents, antiandrogens, antiarrhythmic agents, antiasthmatic agents, anticholinergic agents, anticholinesterase agents, anticoagulants, antidiabetic agents, antidiarrheal agents, antidiuretic, antiemetic and prokinetic agents, antiepileptic agents, antiestrogens, antifungal agents, antihypertensive agents, antimicrobial agents, anti igraine agents, antimuscarinic agents, antineoplastic agents, antiparasitic agents, antiparkinson's agents, antiplatelet agents, antiprogestins, antithyroid agents, antitussives, antiviral agents, atypical antidepressants, azaspirodecanediones, barbiturates, benzodiazepines, benzothiadiazides, beta-adrenergic agonists, beta- adrenergic antagonists, selective beta-one-adrenergic antagonists, selective beta-two-adrenergic agonists, bile salts, agents affecting volume and composition of body fluids, butyrophenones, agents affecting calcification, calcium channel blockers, cardiovascular drugs, catecholamines and sympathomimetic drugs, cholinergic agonists, cholinesterase reactivators, dermatological agents, diphenylbutylpiperidines, diuretics, ergot alkaloids, estrogens, ganglionic blocking agents, ganglionic stimulating agents, hydantoins, agents for control of gastric acidity and treatment of peptic ulcers, hematopoietic agents, histamines, histamine antagonists, 5-hydroxytryptamine antagonists, drugs for the treatment of hyperlipoproteinemia, hypnotics and sedatives, immunosuppressive agents, laxatives, methylxanthines, monoamine oxidase inhibitors, neuromuscular blocking agents, organic nitrates, opioid analgesics and antagonists, pancreatic enzymes, phenothiazines, progestins, prostaglandins, agents for the treatment of psychiatric disorders, retinoids, sodium channel blockers, agents for spasticity and acute muscle spasms, succinimides, thioxanthenes, thrombolytic agents, thyroid agents, tricyclic antidepressants, inhibitors of tubular transport of organic compounds, drugs affecting uterine motility, vasodilators, vitamins and the like.

Exemplary drugs that can be delivered by the devices of this invention, include pilocarpine, nystatin, cetylpyridiniurn chloride, sumatriptan, nicotine, ergotamine, dihydroergotamine, chlorhexidine, clonidine, sodium fluoride, prochlorperazine edisylate, ferrous sulfate, aminocaproic acid, potassium chloride, mecamylamine hydrochloride, procainamide hydrochloride, amphetamine sulfate, benzphetamine hydrochloride, isoproterenol sulfate, methamphetamine hydrochloride, phenmetrazine hydrochloride, bethanechol chloride, methacholine chloride, atropine sulfate, methscopolamine bromide, isopropa ide iodide, tridihexethyl chloride, phenformin hydrochloride, methylphenidate hydrochloride, oxprenolol hydrochloride, metoprolol tartrate, cimetidine hydrochloride, retin A, diphenidol, meclizine hydrochloride, prochlorperazine maleate, phenoxybenzamine, thiethylperazine maleate, anisindione, diphenadione erythrityl tetranitrate, digoxin, isoflurophate, reserpine, acetazolamide, methazolamide, bendroflumethiazide, chlorpropamide, tolazamide, chlormadinone acetate, phenaglycodol, allopurinol, aluminum aspirin, methotrexate, acetyl sulfisoxazole, erythro ycin, progestins, estrogenic progestational hormones, corticosteroids, hydrocortisone, hydrocorticosterone acetate, cortisone acetate, triamcinolone, testosterone, testosterone esters, methyltesterone, 170-estradiol , ethinyl estradiol, ethinyl estradiol 3-methyl ether, prednisolone, 17J-hydroxyprogesterone acetate, 19- nor-progesterone, norgestrel , norethindrone, progesterone, norgesterone, norethynodrel , and the like. Examples of other drugs that can be delivered by the device include aspirin, indomethacin, naproxen, fenoprofen, sulindac, diclofenac, ibuprofen, indoprofen, nitroglycerin, propranolol, metoprolol, valproate, oxprenolol, timolol, atenolol, alprenolol, cimetidine, clonidine, imipramine, levodopa, chlorpromazine, reserpine, methyl-dopa, dihydroxyphenylalanine, pivaloyloxyethyl ester of α-methyldopa hydrochloride, theophylline, calcium gluconate, ferrous lactate, vincamine, diazepam, phenoxybenzamine, α-blocking agents, polypeptides, proteins, insulin and the like. The beneficial drugs are known in the art in the current Physicians' Desk Reference 1992, 46th Ed., published by Medical Economics Data, Montvale, NJ and the like.

The beneficial agent can be in various forms, such as uncharged molecules, molecular complexes, pharmacologically acceptable salts such as hydrochloride, hydrobromides, sulfate, laurylate, palmitate, phosphate, nitrite, borate, acetate, maleate, tartrate, oleate, and salicylate. For acid drugs, salts of metals, amines or organic cations, for example, quaternary ammonium can be used. Derivatives of beneficial agents such as esters, ethers and amides can be used. Beneficial agents broadly includes any active substance for producing a localized effect at the administration site or a systemic effect at a site remote from the administration site.

Agents that can be dispensed by the fluid driven dispensing device include drugs, antibacterials, antifungals, plant growth promoters, surfactants, chemical reactants, and the like. The fluid driven dispensing device described herein is particularly useful for the long-term administration of pharmaceutical compositions such as insulin, analgesics, anti-nausea and anti-cancer drugs.

While certain preferred embodiments of the present invention have been selected for illustration in the drawings and have been selected for illustration in the drawings and have been described in detail herein, the illustrated embodiments should not be construed as limiting and those skilled in the art will appreciate that various modifications, changes, additions and omissions to the illustrated embodiments amy be made without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

WE CLAIM :

1. A fluid driven dispensing device for delivering an agent into an environment of use, said device comprising: a) housing means; b) piston means slidably received within said housing means, said piston means having first and second ends, said first end having a cross-sectional area greater than said second end; c) a beneficial agent compartment formed between said housing means and said first end of said piston means; d) a driving compartment formed between said housing means and said second end of said piston means; and e) engine retaining means for maintaining an engine means actuatable by a fluid adjacent said driving compartment; whereby a given volume of fluid delivered to said driving compartment from said engine means will dispense a larger volume from said beneficial agent compartment.

2. The device of claim 1 wherein the area of said first end is at least 1.5 times greater than the area of said second end.

3. The device of claim 1 wherein the area of said first end is between 3 and 10 times greater than the area of said second end.

4. The device of claim 1 wherein the housing means comprises a syringe housing containing the agent compartment, an amplification housing containing the driving compartment and a driving housing containing the reservoir fluid.

5. The device of claim 1 wherein the engine means is an osmotic engine.

6. The device of claim 1 wherein a sealing means provides a fluid tight seal between the piston means and the driving compartment.

7. The device of claim 1 further comprising: g) an overflow reservoir; and h) valve means disposed in fluid communicating relationship to said driving compartment and said overflow reservoir, said valve means being movable from a closed position to an open position permitting fluid flow from said driving compartment to said overflow reservoir.

8. The device of claim 7 wherein said overflow reservoir is within said housing means and surrounds at least a portion of said piston means.

9. The device of claim 1 further comprising: i) an osmotic engine in said retaining means, said engine comprising: ii) an osmotic solute; iii) a wall portion permeable to said fluid disposed between said solute and said reservoir means; and iv) outlet means in fluid communicating relationship to said driving compartment.

10. A fluid driven dispensing device for delivering a beneficial agent to an environment of use comprising: a) a syringe housing adapted to contain said agent and having outlet means proximate one end thereof; b) an amplification housing attached at one end to the other end of said syringe housing; c) a driving housing attached to the other end of said amplification housing; d) piston means slidably received within said syringe housing and said amplification housing, the end of said piston means within said syringe housing comprising plunger means having a larger cross-sectional area -than the end of said piston proximate said reservoir means, said piston means being movable from a first position proximate the amplification housing end of the syringe housing to a second position proximate the outlet means; and e) means for retaining an engine in fluid communicating relationship with both said reservoir means and said piston means; whereby a given volume of fluid delivered to said piston means from said engine means will dispense a larger volume from said syringe housing.

11. The device of claim 10 wherein the ratio of the cross- sectional area of said plunger means to the opposite end of said piston means is at least 1.5 to 1.

12. The device of claim 10 wherein the ratio of the cross- sectional area of said plunger means to the opposite end of said piston means is between 3 and 10 to 1.

13. The device of claim 9 further comprising: f) an engine in said retaining means in fluid sealing relationship between said driving housing and the end of said piston opposite said plunger means, said engine comprising: i) an osmotic solute; ii) a wall portion permeable to, and disposed to be in contact with, fluid contained within said reservoir means, said wall portion disposed separating said solute from fluid within said reservoir means; and iii) outlet means in fluid communicating relationship to the end of said piston opposite said plunger means.

14. The device of claim 13 further comprising: g) collapsible enclosure means enclosing a reservoir fluid for said osmotic engine, said enclosure means being disposed within said driving housing; and h) releasing means for puncturing said enclosure means; whereby said reservoir fluid may be released into said driving housing and into contact with said osmotic engine.

15. The device of claim 14 further comprising: i) vent means for said driving housing to permit air to enter said driving housing and permit collapse of said enclosure means.

16. The device of claim 15 further comprising: jj means on said driving housing for placing said releasing means in puncturing relationship to said enclosure means.

17. The device of claim 14 wherein said releasing means provides a fluid flow path for said reservoir fluid between said driving housing and said osmotic engine.

18. The device of claim 15 further comprising: k) valve means operable to divert the flow of fluid from said osmotic engine away from the end of said piston opposite said plunger means.

19. In a fluid driven dispensing device comprising: a) piston means having first and second ends; and b) housing means slidably receiving said piston means, the first end of said housing forming an agent dispensing compartment having outlet means through which an agent may be displaced by movement of the first end of said piston, the second end of said housing being adapted to maintain an osmotic engine in fluid discharging relationship to said second end of said piston and to contain a reservoir fluid for said osmotic engine; the improvement wherein the cross-sectional area of said first end of said piston is at least 1.5 time the cross-sectional area of said second end whereby a given volume of fluid discharged from said osmotic engine will displace a greater volume of agent through said outlet means.

20. The device of claim 19 wherein the cross-sectional area of said first end as between 3 and 10 time greater than that of said second end.

21. The device of claim 19 wherein said improvement further comprises valve means operable to divert the flow of fluid discharged from said osmotic engine away from the second end of said piston.

22. The device of claim 19 wherein at least a portion of the fluid discharged from the osmotic engine is a gas.

23. The device of claim 19 wherein said piston comprises a inner piston that telescopes from an outer piston.