Osmotically Driven Fluid Dispenser

This invention relates to an osmotic dispenser, and, more especially, to an osmotic dispenser, simple in construction, capable of dispensing a fluid, such as an active agent at an osmotically controlled rate over a continuous and prolonged period of time.

The invention is an osmotically driven fluid dispenser for use in an aqueous environment consisting essentially of:

A. A SINGLE SHAPE RETAINING CLOSED CANISTER THAT DEFINES THE EXTERIOR OF THE DISPENSER WHICH EXTERIOR IS EXPOSED COMPLETELY TO THE AQUEOUS ENVIRONMENT, AT LEAST A PORTION OF THE WALL OF THE CANISTER BEING MADE OF A MATERIAL OF CONTROLLED PERMEABILITY TO WATER;

B. AN OSMOTICALLY EFFECTIVE SOLUTE CONFINED WITHIN THE CANISTER WHICH, IN AQUEOUS SOLUTION, EXHIBITS AN OSMOTIC PRESSURE GRADIENT ACROSS SAID PORTION OF THE CANISTER WALL AGAINST THE WATER OF SAID ENVIRONMENT, SAID CANISTER BEING SUBSTANTIALLY IMPERMEABLE TO THE SOLUTE;

C. AN OUTLET IN THE CANISTER WALL; AND

D. A FLEXIBLE BAG ADAPTED TO HOLD THE FLUID TO BE DISPENSED AND HOUSED WITHIN THE CANISTER WITH ITS OPEN END IN SEALED CONTACT WITH THE CANISTER WALL SUCH THAT THE OUTLET COMMUNICATES WITH ITS INTERIOR AND ITS INTERIOR IS CLOSED TO THE SOLUTE AND AQEUOUS SOLUTION THEREOF WITH THE REMAINDER OF THE BAG BEING SPACED FROM THE CANISTER WALL AND GENERALLY UNSUPPORTED THEREBY, THE EXTERIOR OF SAID REMAINDER BEING EXPOSED TO THE SOLUTE AND AQEUOUS SOLUTION THEREOF, WHEREBY WATER IS IMBIBED INTO THE CANISTER FROM THE ENVIRONMENT THROUGH SAID PORTION OF THE CANISTER WALL BY THE SOLUTE AND THE IMBIBED WATER EXERTS HYDRAULIC PRESSURE UNIFORMLY ON THE EXTERIOR OF THE FLEXIBLE BAG EXPOSED THERETO, CAUSING THE BAG TO COLLAPSE INWARDLY THUS SQUEEZING THE FLUID OUT OF THE BAG VIA THE OUTLET.

The prior art to the invention is described in detail in the file of patent application Ser. No. 291,686, filed Sept. 25, 1972, now U.S. Pat. No. 3,995,631.

In the drawings:

FIG. 1 is a cross-sectional view of an osmotic dispenser of this invention;

FIG. 1a is a top view of the osmotic dispenser of FIG. 1;

FIG. 2 is a cross-sectional view of another osmotic dispenser of this invention;

FIG. 3 is a cross-sectional view of yet another osmotic dispenser of this invention;

FIG. 4 is a cross-sectional view of still another osmotic dispenser of this invention; and

FIG. 5 is an exploded view of the dispenser of FIG. 4;

FIG. 6 is a schematic view of the construction and fabrication of still another osmotic dispenser of this invention, designated as the "mini-pump" embodiment; and

FIG. 7 is a cross-sectional view of another mini-pump osmotic dispenser of this invention.

The expression "active agent" as used herein denotes any drug (as defined, infra); composition in any way affecting any biological entity; substance having a nutrient or stimulating action, or growth inhibiting, destroying or any regulating action on plant growth, controlled or otherwise; substance to be assimilated by any organism, e.g., human being, animal, or lower order organism, for its nourishment or for regulating its growth; substance exhibiting any of the above activities to be directly applied to the habitat, surroundings or environment of any of the above organisms; and substance having any other effect on any other environment, especially any aqueous environment.

Therefore, suitable active agents for use with the dispenser of this invention include, without limitation, those which are generally capable of:

1. Preventing, alleviating, treating or curing abnormal of pathological conditions of the living body by such means as destroying a parasitic organism or limiting the effect of the disease or abnormality by chemically altering the physiology of the host or parasite;

2. Maintaining, increasing, decreasing, limiting or destroying a physiologic body or plant function, e.g., vitamin compositions, sex sterilants, fertility inhibitors, fertility promoters, growth promoters, and the like;

3. Diagnosing a physiological condition or state;

4. Controlling or protecting an environment or living body by attracting, disabling, inibiting, killing, modifying, repelling or retarding an animal or microorganism, such as food and non-food baits, attractants and lures, biocides, pesticides, algicides, parasiticides, rodenticides, insecticides, fungicides, and the like;

5. Preserving, disinfecting or sterilizing; and

6. Controlling or affecting generically an enviroment, as by introducing a catalyst or metering a reactant into a reacting chemical system, or by effecting any chemical process therein, such as a fermentation, including propagation and/or attenuation of a microorganism.

The term "aqueous environment," as used hereinabove and herein, means an environment that surrounds the external surface of the canister of the dispenser and that contains sufficient water for absorption into the dispenser to develop the needed osmotic pressure on which its motive force depends. This term does not include sources of water that are affixed to the exterior of the dispenser.

In one embodiment in accordance with this invention, as illustrated in FIG. 1, an osmotic dispenser 10 is comprised of a rigid canister 12, at least a portion of the wall membrane defining the same exhibiting controlled permeability to water, as hereinafter more fully explained. Housed within the canister 12 is a flexible bag 14 of relatively impervious material. The said flexible bag 14 contains the fluid to be dispensed 16, advantageously a drug formulation in a liquid, suspension, gel, paste or other fluid state. The volume of the canister 12, other than that occupied by the flexible bag 14 and fluid 16, is occupied by a solution 18 of an osmotically effective solute which exhibits an osmotic pressure gradient against the water in the environment. The open end of canister 12 is tightly sealed or closed off with rigid, impervious dispensing head, plug or delivery cap 20, with the open end of the flexible bag 14 being concentrically secured therebetween (see also FIG. 1a). In this manner a tight barrier is maintained between and among the fluid 16 in the flexible bag 14, the solution 18 in the canister 12, and the external environment of the dispenser 10. Without this tight barrier, undesirable contamination could take place. The dispensing head 20 is preferably snapped or press-fit in place with the flexible bag 14 either being already circumferentially tightly secured thereto or to the upper, inner periphery of the canister 12. Alternatively, these three elements may conveniently be heat sealed together, and, as an aid in maintaining the tight barrier, a chamfered polycarbonate retaining ring 22 may optionally be press-fit about the top of the dispenser 10. An outlet 24 extends through head 20 and provides communication from the interior of the flexible bag 14 to the exterior of the dispenser 10, said outlet advantageously being approximately 0.0625 inch in diameter. As seen in FIG. 1, bag 14, except for the end that is secured between the wall of canister 12 and head 20, is spaced from the wall of the canister and is generally unsupported thereby. In other words the bag 14 hangs freely in canister 12 without any lateral or bottom support. The exterior surface of bag 14 except for said end, is exposed to solution 18.

When the fluid is a drug or other agent for treating a living organism, dispenser 10 is either physically inserted or surgically implanted in the body of the organism, typically a mammal, or is administered via the gastrointestinal tract. Once in place, water will be absorbed therein from either body tissues or body fluids through the area of the canister 12 which exhibits the controlled permeability to water and in an effort to reach osmotic equilibrium, i.e., a transition from hypertonicity to isotonicity. As the fluid flows by osmosis into the canister 12 the volume of the solution 18 is thus increased and corresponding pressure is exerted uniformly, multidirectly and inwardly against the exterior surface of bag 14 that is exposed to solution 18. Such pressure serves to squeeze the drug formulation 16 out of the bag 14 through the outlet 24 at an osmotically controlled and constant rate into the external environment. There is accordingly provided the gradual and controlled constant release of drug or similar agent directly to the body or affected organ thereof over a prolonged period of time. Also, because of the nature of the pressure exerted on bag 14, bag 14 collapses uniformly inwardly thus insuring substantially complete dispensing of formulation 16.

The design of the canister 12 is such that a given area of the wall members defining the same displays permeability to water at an osmotically controlled rate. Said canister, therefore, is either of unit or composite construction and is advantageously comprised of a semi-permeable membrane, with same either defining an integral wall member of the canister, or a lining, or in some manner is laminated thereto or otherwise disposed in the desired functional relationship.

In FIG. 2, for example, there is illustrated an osmotic active agent dispenser 10 wherein the canister 12 is comprised of rigid, impervious, cylindrical plastic side wall member 30 and bottom wall member 32 integral therewith. Bored into the said bottom wall member 32 are a plurality of orifices or ducts 34, each preferably about 1/16 inch in diameter. It will thus be appreciated that, being highly porous, only the bottom wall member 32 of the canister 12 is capable of admitting water into the device, the said cylindrical side wall member 30 remaining fluid impenetrable. It is not intended that the highly porous bottom wall member 32 in any way act as a barrier to or restrict the transport of fluid. Securedly affixed and supported atop the said perforated bottom wall member 32 is a flat disc 36 of membrane which exhibits controlled permeability to external fluid, e.g., water. The membrane 36 may, for example, either be ashesively secured in place or may be lined or laminated to, or cast from solution atop the said bottom wall member 32. The aforementioned casting atop the porous wall 32 is advantageously perfected by depositing the film or disc from a solution of membrane forming material in a solvent, e.g., a 20% solution of cellulose acetate in an acetone-ethanol-ethyl lactate mixed solvent, 65% -- 20% -- 15%, respectively. In casting the film, care should be taken that the pores of the wall member 32 do not become clogged. And it is of course intended that the seal between the membrane 36 and the porous wall 32 be watertight such that fluid is permitted access to the interior of the device only by diffusing by osmosis through the said membrane 36. As too will be appreciated, it is also possible that the membrane 36 be affixed beneath the said bottom wall member 32. The design of the FIG. 2 is moreover unique in that it requires a membrane of but limited surface area relative to the overall dimensions of the canister. This because of the ready availability of the highly water-permeable cellulose acetate membranes designed for use in reverse osmosis processes for water desalination. These membranes, typically and preferably anisotropic membranes, are highly permeable to water (allow relatively rapid rates of water transmission) but are relatively impermeable to salt, thus permitting their use in relatively small exposure area devices. And water will migrate into the dispenser only at the point of exposure of the membrane 36 with the outside environment via the ducts 34.

Optionally, in an alternative embodiment of the invention, a separator of porous paper, fabric or the like can conveniently be disposed between the bottom wall member 32 and the membrane 36. This prevents the membrane from being punctured or drawn into too tight a contact with the canister, thereby assuring that the entire membrane is exposed to the fluid environment. The immediately above option also applies to a device such as illustrated in FIG. 3. Furthermore, use of the porous separator aids in the aforesaid embodiment of casting the membrane from solution, same providing a ready-made molding or casting surface with no danger of orifices 34 clogging.

In FIG. 3 there is depicted an osmotic fluid dispenser 10 which allows for higher available exposure area of membrane 36 and, accordingly, which design takes advantage of the availability of a far greater number of membranes than the semi-permeable, anisotropic cellulose acetate membranes of the type used in reverse osmosis water desalination. In this embodiment it is the rigid, impervious, cylindrical plastic side wall member 30 which is provided with the plurality of orifices or ducts 34, again, each preferably being about 1/16 inch in diameter, and it is this perforated wall 30 which is tightly fitted, as in FIG. 2, with the membrane 36, in this instance a membrane of cylindrical configuration. Many and varied designs intermediate in construction between the designs of the FIG. 2 and FIG. 3 dispensers, insofar as available exposure area of membrane is concerned, are of course within the scope of the invention.

In some instances, the dispenser is of insufficient specific gravity to maintain placement at the desired location. For example, for use in the rumen of polygastric animals, the weight should be sufficient to provide a specific gravity of at least 1.5. In those instances of insufficient specific gravity, therefore, a weight of ballast can be placed in the dispenser, such as the steel ball 38 of FIG. 3. Other suitable weights comprise iron plugs, iron ore tablets, brass plugs, ceramic plugs, or the like.

When the fluid 16 is other than a drug or similar agent, or is intended for use other than in a living organism, the device is introduced into the desired aqueous environment to produce the desired effect exactly as would be any of the known means for accomplishing a like result.

If desired, long flexible tubing of polyethylene or the like can be extended from the dispensing head of the dispenser of either of FIGS. 1, 2 or 3. In such manner the dispenser can be deposited at a site remote from the desired point of application and still release its active agent contents through the dispensing head and then through the tube directly to said point. This permits placement of the dispenser in a fluid environment and release of the active agent into another environment which need not be fluid. The dispensing head can also be provided with a check valve, for example, a one way bell valve, to prevent back flow of active agent or other materials from the external environment into the dispenser.

Moreover, a dispenser of either FIG. 1, FIG. 2 or FIG. 3 type is admirably suited for the continuous administration of the antibiotic oxytetracycline to beef cattle from the rumen. This because such devices can easily be fabricated of a size, weight and shape as to be retained in the rumen of polygastric animals to release drug or similar agent thereto at a carefully controlled rate. Other variations on the basic theme would be readily apparent to the skilled artisan. Although particular cnfigurations may be designed for specific body uses, e.g., for use in the stomach or rumen, uterus, vagina, bladder, etc., each of these configurations is applicable to use in other environments. For another example, an ocular insert can similarly easily be fabricated of a size and shape adapted for insertion in the eye, e.g., the cul-de-sac of the conjunctiva between the sclera of the eyeball and the lower lid, to be held in place against the eyeball by the pressure of the lid. Compare in this respect U.S. Pat. Nos. 3,416,530, and 3,618,604.

The membrane 36 of FIGS. 2 and 3 and that portion of the wall members defining the canister 12 of FIG. 1 which exhibits controlled permeability to external fluids can be formed from a wide variety of materials permeable or semi-permeable to solvent but not to solute, i.e., those suitable for the construction of an osmotic cell. For best results, the membrane should be substantially impermeable to passage of the osmotically effective solute so as to prevent loss thereof. Typical membranes are isotropic membranes such as unplasticized cellulose acetate, plasticized cellulose acetate, reinforced cellulose acetate, cellulose di- and triacetate, ethyl cellulose; anisotropic reverse osmosis membranes which typically are made of cellulose acetate; silicone rubbers, polyurethanes, natural rubber, and hydrolyzed ethylene/vinyl acetate copolymers. Isotropic membranes have less water permeability than do the anisotropic membranes. Also, with both types of membranes, increasing the acetate content of the cellulose acetate polymer decreases the water permeability. Since, as previously described, the surface area of the membrane is relatively limited in a dispenser of FIG. 2 type, it will be preferred to use semi-permeable membranes allowing relatively rapid water transmission in this general category of dispensers. Thus, in such embodiments the anisotropic membranes are the preferred. A cellulose acetate membrane suitable for this limited surface area application is Eastman Chemical Products Type RO 97, which is rated to be permeable to 1.5 to 2 cc/cm.sup.2 /day at atmospheric pressure, against a saturated solution of K.sub.2 SO.sub.4 at 39.degree. C. A specific example of the design of FIG. 2 constructed with polymethylmethacrylate dispensing head and having an inner diameter of 1.9 cm is capable of delivering 4 to 6 cc of active agent, advantageously a drug, per day. In one specific embodiment of a dispenser of FIG. 3 type, the membrane used was an isotropic cellulose acetate membrane, with no plasticizer, having an acetate substitution of 2.4, being 3 mils thick, and passing water at the rate of 70 mg/cm.sup.2 per day against a saturated magnesium sulfate solution of 39.degree. C. The membranes too are insoluble, and chemically compatible with the salt solution and any excess solute therein. For drug depot applications as heretofore described, the membranes are also biologically inert, non-irritating to body tissues and nonallergenic. For devices designed to deliver active agents relatively rapidly for a limited period, membranes of controlled high fluid permeability are indicated; membranes of lower fluid permeability are used to provide slower and more prolonged delivery.

The impermeable bag 14 of the osmotic dispensers of the figures of the drawing containing the active agent composition should be substantially impermeable both the fluid, and the other elements of the environment on which a device of such type is intended to be placed, the osmotically effective solute, and components of the active agent composition. Typical materials for use as the impermeable bag include polyethylene, polyethylene terephthalate (Mylar), plasticized polyvinyl chloride, metal-foil polyethylene laminates, neoprene rubber, natural gum rubber, and Pliofilm (rubber hydrochloride). These materials are additionally flexible, insoluble and chemically compatible with the active agent therein, and, in the instance of providing a drug or like depot within the body of a living organism, are biologically inert, non-irritating to body tissues and non-allergenic.

The impermeable plastic canister 12 of FIGS. 2 and 3 and impermeable portions of the canister 12 of FIG. 1 too are insoluble and can be formed of polystyrene, polyethylene, polypropylene, polyvinyl chloride, reinforced epoxy resin, polymethylmethacrylate, etc., sheet metal (e.g., aluminum, copper, steel, etc.), galvanized pipe, or styrene/acrylonitrile copolymer. It is of course intended that such casing or shell act as a barrier to the transport of fluid, except at the areas of perforation. Again, for drug depot applications the same are advantageously biologically inert, non-irritating to body tissues and non-allergenic. The dispensing head 20 and the retaining ring 22 can be formed of materials indentical to those used for fabricating the canisters 12 with polycarbonate being additionally well suited for the ring 22. Especially preferred of the above are the impermeable or refractory plastics.

Many other materials including those which are biologically acceptable are suitable for fabrication of the several component parts of the device of this invention. While the said several component parts of the device of the invention have previously been described as being insoluble under the conditions and in the environment of intended use, it is also within the scope of the invention that such materials be insoluble only during the period of said intended use; thereafter dissolving away in the environment of the device. Thus, a dispenser is here contemplated which is unaffected by its environment, solubility-wise, at the situs of use, or which is only slightly soluble during the period of intended use, such that once its active agent content has been discharged it will then dissolve or erode away leaving no objectionable residue or empty container at the said situs of use.

It is further within the scope of the invention to optionally provide the subject dispenser with a self-contained fluid supply or separate fluid compartment, as in the first mentioned Rose and Nelson publication, supra.

The relative thicknesses of the various membranes comprising the dispensers of the invention, as well as the relative thickness of the various canisters can vary widely and are not limitations on the invention. Typically, however, each canister has a wall thickness of 0.5 to 50 mils, preferably of 5 to 50 mils, and the fluid permeable membranes have a wall thickness of 1 to 10 mils.

One specific embodiment of a dispenser fabricated in accordance with the invention, and as illustrated in FIGS. 4 and 5, fitted with a 3 mils thick semi-permeable membrane 36 and a 2 mils thick flexible active agent bag 14, and having the following dimensions and specifications:

Outer diameter of dispenser: 1.125 inch

Wall thickness of canister 12: 0.125 inch

Inner diameter of dispenser: 0.875 inch

Overall length: 2.5 inch

External volume: 2.45 inch .sup.3

Internal volume: 1.24 inch .sup.3

Overall dispenser density: 1.5

Available membrane area: 0.44 inch .sup.2

Active agent volume: 0.94 inch .sup.3

Active agent density: 1.2

Active agent: Approximately 60 percent tetracycline hydrochloride dispersed in 40 percent polyethylene glycol medium;

Osmotic solution: Saturated aqueous solution of K.sub.2 SO.sub.4 containing sufficient excess solute in solid form to maintain solution saturated over a period of at least 3 days;

Water permeable membrane: Cellulose diacetate, with a degree of acetyl substitution of 2.4;

Canister 12: Soft polyethylene;

Threaded end cap 32: Soft polyethylene;

Delivery cap 20: Soft polyethylene;

Active agent bag 14: Polyethylene;

Chamfered ring 22: Polycarbonate;

Membrane support 40: Polystryene:

Diameter of delivery port 24: 0.0625 inch;

Diameter of orifices in cap 32: 0.0625 inch;

Diameter of orifices in support 40: 0.1250 inch;

is capable of delivering 5 gm of the active drug per day, over a period of 3 days, when administered to the rumen of a 500 pound calf, whereat it is retained, via the gastrointestinal tract. It will be appreciated that the design of the FIG. 4 and FIG. 5 device is quite similar to that of FIG. 2, with the most salient distinctions therebetween residing, in the FIGS. 4 and 5 device, in the perforated end cap construction 32 which is threaded onto the canister 12 and fitted with a rubber O-ring 42 to prevent leakage at the point of the thread fit. The cap 32 houses the membrane 36 and the membrane support 40. Of course, the greater the free space or total open surface area of the plurality of ducts bored into the end cap 32, the greater the amount of the membrane 36 which is exposed to the aqueous or other fluid environment. Likewise, the greater the open surface area of the plurality of ducts bored into the membrane support 40, the more readily the fluid diffuses into the compartment 24. As in the designs of FIGS. 2 and 3, it is again optional that a separator of porous paper, fabric or the like can be placed between either or both of the membrane support 40 and end cap 32 and the semi-permeable membrane 36. Same, as heretofore mentioned, prevents the membrane from being punctured or drawn into too tight a contact with its housing, thereby additionally assuring that the entire membrane is exposed to the aqueous environment.

In still another embodiment in accordance with this invention, hereinafter designated the mini-pump embodiment and as illustrated in the schematic drawing of FIG. 6, a modular osmotic fluid dispenser is constructed which is conceptually similar to the devices illustrated in the FIGS. 1-3. For the fabrication of the bag for the mini-pump, corresponding to the bag 14 of FIG. 1, there are first selected the raw materials consisting of (1) thin walled polyethylene tubing of a size according to the drug volume required, (2) two identical polyethylene 20 delivery and fill tubes (each having, e.g., 0.043 inch outer diameter and 0.015 inch inner diameter) and (3) a, for example, 0.010 inch needle or wire cleaner. Note the step I of FIG. 6. Next, as illustrated in the step II of FIG. 6, the wire is placed within the polyethylene 20 tubes and the resultant construction is arranged within the prospective bag, as depicted. The delivery and fill tubes are then heat sealed on Vertrod to either end of the larger bag polyethylene tubing and the wire is removed. In step III, via the fill tube conduit, the bag is filled with drug formulation in fluid form. An added overflow tube catches and retains formulation displaced as the bottom end of the device is sealed. This overflow tube is then removed and the delivery tube is sealed at its end. The final preparation of the bag is illustrated in step IV wherein the fill tube is removed by severing, the various seals are trimmed to minimize their size, and the delivery tube is roughened with emery paper. At this point in the operation the bag containing the formulation is conveniently pressure tested by mere squeezing.

The ultimate mini-pump construction is completed by following the procedure outlined in the steps V-VII of FIG. 6. First is a salt encapsulation, namely, a mold (not shown) is filled with a gelatin-salt matrix (by "salt" there is intended any of those osmotically effective solutes hereinafter described); the previously fabricated bag is then placed in the said mold and same is compressed by an convenient means (not shown), for example, a typical C-clamp. Next, the mold, bag and gelatin-salt matrix are frozen. Half of the mold is then removed and the half containing the pump fabrication is dried overnight in an oven. See step V for the appearance of the mini-pump subsequent to the encapsulation technique. Optionally, see step VI, the salt encapsulated drug bag can be coated with a thin layer of gelatin, by simply dipping same in a gelatin solution and permitting the coating to dry to hardness, to form a smooth surface more susceptible to the membrane coating operation of step VII. In step VII the construction of the minipump is completed by coating either the step V or step VI assembly with a layer of membrane material of the type previously described. For example, such assemblies can conveniently be coated by more dipping in an, e.g., cellulose acetate solution, permitting one hour to lapse between successive dips, and thence drying the thus membrane-coated construction for about 48 hours. The membrane coat is sufficiently rigid in and of itself such that as water permeates from an external, aqueous environment through said permeable membrane cost and migrates by osmosis into the salt, thus forming an osmotically effective solution therewith which initiates the phenomenon of osmosis due to the tendency towards osmotic equilibrium with the said environment, the said membrane cost is able to withstand this increase in volume within the mini-pump and concomitant mechanical deflating force generated on the flexible bag, which force in turn ejects the drug formulation out of the dispenser at an osmotically controlled rate over a prolonged period of time. As in the dispenser of FIG. 1-5, the bag of the dispenser of FIG. 6, except at its delivery tube, is spaced from and generally unsupported by the membrane coat.

The device of FIG. 6 is used exactly as the previously described dispensers, with the advantages of its smaller size being manifest (the illustrations of FIG. 6, for point of reference, are about twice actual size). For example, the distal end of the delivery tube can conveniently be cut off with a scalpel; placed, implanted or administered to a delivery environment; and the spent pump evidences complete discharge or delivery of its content. The various materials comprising the said mini-pump, moreover, substantially correspond to those materials comprising equivalent and corresponding components of those osmotic dispensers heretofore described and illustrated.

The novel and useful osmotic fluid dispensing device of FIG. 6 as manufactured according to the mode and manner of the invention, and as disclosed above, is not to be construed as limiting as these and other embodiments can also be fabricated in accordance with the spirit of the invention. For example, the device of FIG. 6 is manufactured, as shown in FIG. 7, of a wall 41 comprised of a flexible, collapsible material essentially impermeable to a fluid and substantially impermeable to an agent. The wall surrounds a chamber or bag defined by the wall's inner surface 42 as a means for containing the agent.

The agent can be added at the time the device is first made or the device can be stored and charged with the agent at a future time. Suitable materials for forming the wall are the impermeable materials set forth above and these include polyethylene, polypropylene, polyethylene terephthalate, plasticized polyvinyl chloride, polypropylene laminated with metal foils such as thin tin, polypropylene laminated with metal foils such as thin tin, aluminum foil, cross-linked polyester, commercially available copolymers, and the like. The device is provided with an outlet 43 for releasing the agent from the chamber to the exterior of the osmotic dispensing device, and this outlet can be a passageway that communicates with the chamber and the exterior environment, a capillary, a porous fiber, a sintered plug and the like. Distant from the outlet 43 is optionally located a filling port, not shown in FIG. 7, that communicates with the chamber that is integrally formed or suitably joined to the osmotic dispensing device. The filling port can be a silicon plug, an impermeable cross-linked rubber diaphragm pierceable by a filling needle, a tube that can be closed after the chamber is filled by heating and squeezing the tube, a valve, and the like. The impermeable wall bears on its outer surface a coating 44 comprised of at least one compound that can exhibit an osmotic pressure gradient against a fluid when the device is subsequently placed in the environment of use. The osmotically effective compound is applied to the wall by standard methods such as dipping, spraying, depositing, laminating, filming and the like to give the corresponding coat, film, laminate and the like; and, which methods and results are deemed for the purpose of this invention as functional equivalents. Representative of osmotically effective compounds suitable for this purpose, are inorganic and organic compounds such as magnesium sulphate, magnesium chloride, sodium chloride, lithium chloride sodium carbonate, sodium succinate, mixtures thereof, and other osmotic attractants as described in this disclosure. The compounds can be applied in pure form, that is, by mixing the compound with a suitable solvent followed by dipping or brushing the solution onto the walls and then evaporating the solvent. The compound can also be applied by mixing it with a binder such as ethylcellulose, gelatin, ethylmethylcellulose, hydroxypropyl methyl cellulose, sodium cellulose sulfate, polyvinylalcohol, polyethylene glycol, Irish moss, casein and the like, mixed with the binder alone, or with a solvent which is applied to the wall by stanndard techniques. The amount of binder mixed with the compound is an amount sufficient to bind the compouund to the wall and it is usually, when used, about 0.001% to 20% or higher, for 1 to 1000 grams of compound. When a solvent is used any conventional inorganic or organic solvent that does not adversely affect the parts of the device and can be suitably removed by evaporation, drying, and the like can be used as a manufacturing means.

Distant from the inner impermeable wall, that is, the outer wall of the osmotic device, and in proximate contact with the osmotically effective compounds is a wall 45 comprised in at least a part of a semi-permeable membrane that lets an external fluid permeate therethrough while being substantially impermeable to the osmotic attractants. These membranes are applied by conventional techniques and they include cellulose acetate, reinforced cellulose acetate, polyurethanes, and the semi-permeable membranes as disclosed in this specification. This device offers an improved advantage that it can be filled and stored without any adverse effects on the agent or its release from the device since the device commences operation when placed in the environment of use.

Any of the drugs used to treat the animals, including humans and avians, both typical, logic and systemic, can be compartmentalized in any of the osmotic dispensers of this invention. "Drug" is used herein in its broadest sense as including any composition or substance that will produce a pharmacological or physiological response.

Suitable drugs for use in therapy with the dispenser of the invention included without limitation:

1. Protein drug such as insulin;

2. Desensitizing agents such as ragweed pollen antigens, hay fever pollen antigens, dust antigen and milk antigen;

3. Vaccines such as small pox, yellow fever, distemper, hog cholera, fowl pox, antivenom, scarlet fever, diphtheria toxoid, tetanus toxoid, pigeon pox, whooping cough, influenzae, rabies, mumps, measles, poliomyelitis, Newcastle disease, etc.;

4. Anti-infectives, such as antibiotics, including penicillin, tetracycline, chlortetracycline, bacitracin, nystatin, streptomycin, neomycin, polymyxin, gramicidin, oxytetracycline, chloramphenicol, and erythromycin; sulfonamides, including sulfacetamide, sulfamethizole, sulfamethazine, sulfadiazine, sulfamerazine, sulfisoxazole; anti-virals including idoxuridine; and other anti-infectives including nitrofurazone and sodium propionate;

5. Anti-allergenics such as antazoline, methapyrilene, chlorpheniramine, pyrilamine and prophenpyridamine;

6. Anti-inflammatories such as hydrocortisone; cortisone, hydrocortisone acetate, dexamethasone, dexamethasone 21-phosphate, fluocinolone, triamcinolone, medrysone, prednisolone, prednisolone 21-phosphate, and prednisolone acetate;

7. Decongestants such as phenylephrine, naphazoline, and tetrahydrozoline:

8. Miotics and anticholinesterases such as pilocarpine, eserine salicylate, carbachol, di-isopropyl fluorophosphate, phospholine iodide, and demecarium bromide;

9. Mydriatics such as atropine sulfate, cyclopentolate, homatropine, scopolamine, tropicamide, eucatropine, and hydroxyamphetamine;

10. Sympathomimetics such as epinephrine;

11. Sedatives and hypnotics such as pentobarbital sodium, phenobarbital, secobarbital sodium, codeine, (.alpha.-bromo-isovaleryl) urea, carbomal;

12. Psychic energizers such ad 3-(2-aminopropyl) indole acetate and 3-(2-aminobutyl) indole acetate;

13. Tranquilizers such as reserpine, chlorpromazine, and thiopropazate;

14. Androgenic steroids such as methyltestosterone and fluoxymesterone;

15. Estrogens such as estrone, 17 .alpha.-estradiol, ethinyl estradiol, and diethyl stilbesterol;

16. Progestational agenst such as progesterone, megestrol, melengestrol, chlormadinone, ethisterone, norethynodrel, 19-norprogesterone, norethindrone, medroxyprogesterone and 17 .alpha.-hydroxyprogesterone;

17. Humoral agents such as the prostaglandins, for example, PGE.sub.1, PGE.sub.2, and PGF.sub.2 ;

18. antipyretics such as aspirin, sodium salicylate, and salicylamide;

19. Antispwsmodics such as atropine, methantheline, papaverine, and methscopolamine bromide;

20. Anti-malarials such as the 4-aminoquinolines, 8-aminoquinolines, chloroquine, and pyrimethamine;

21. Antihistamines such as diphenhydramine, dimenhydrinate, tripelennamine, perphenazine, and carphenazine;

22. Cardioactive agents such as hydrochlorothiazide, flumethiazide, chlorothiazide, and troinitrate;

23. Nutritional agents such as vitamins, essential amino acids and essential fats;

24. Anti-Parkinsonism agents such as L-dopa, (L-3, 4-dihydroxyphenylalanine);

25. Investigative antihypotensive agents such as dopamine, 4-(2-aminoethyl) pyrocatechol.

Other drugs having the same or different physiological activity as those recited above can be employed in osmotic dispensers within the scope of the present invention. Suitable mixtures of drugs can, of course, be dispensed with equal facility as with single component systems.

Drugs can be in various forms, such as uncharged molecules, components of molecular complexes, or non-irritating pharmacologically acceptable salts such as hydrochloride, hydrobromide, sulphate, phosphate, nitrate, borate, acetate, maleate, tartrate, salicylate, etc. For acidic drugs, salts of metals, amines, or organic cations (e.g., quaternary ammonium) can be employed. Furthermore, simple derivatives of the drug (such as ethers, esters, amides, etc.) which have desirable retention and release characteristics but which are easily hydrolyzed by body pH, enzymes, etc., can be employed.

The amount of drug incorporated in the osmotic dispenser varies widely depending on the particular drug, the desired therapeutic effect, and the time span for which it takes the drug to be released. Since a variety of dispensers in a variety of sized and shapes are intended to provide complete dosage regimes for therapy for a variety of maladies, there is no critical upper limit on the amount of drug incorporated in the dispenser. The lower limit too will depend on the activity of the drug and the time span of its release from the dispenser. This it is not practical to define a range for the therapeutically effective amount of drug to be released by the dispenser.

The motive force of the dispenser of this invention depends on the osmotic pressure generated by the solution 18 of the osmotically effective solute confined within the canister 12, which solution exhibits an osmotic pressure gradient against water in the aqueous environment in which the dispenser is placed. Said solution is most preferably a saturated aqueous salt solution. To maintain the solution saturated and therefore to achieve a constant osmotic pressure throughout operation of the dispenser, the canister containing the solution also contains excess solute in solid form. Various osmotically effective solutes can be used. These include magnesium sulphate, magnesium chloride, sodium chloride, potassium sulphate, soidum carbonate, sodium sulphite, sodium sulphate, sodium bicarbonate, potassium acid phthalate, calcium bicarbonate, potassium acid phosphate, raffinose, tartaric acid, succinic acid, calcium succinate, calcium lactate, and magnesium succinate. The excess solid solute can be in the form of dispersed particles or preferably in the form of a pellet. The solution can initially be a solution of the same or of an osmotically effective solute different than the solid excess solute.

The osmotic dispenser can be fabricated in any convenient shape for either physical insertion or implantation in the body, as for administration via the gastrointestinal tract, or for introduction into any desired fluid environment. Dimensions of the device can thus vary widely and are not of controlling importance. The lower limit of the size of the device is governed by the amount of the particular active agent to be supplied to the fluid environment to elicit the desired response, as well as by the form the dosage unit takes, for example, in cases of specific body uses, implantate, bolus, IUD, IVD, vaginal ring, oscular insert, bladder insert, uterine capsule for fertility suppression, artificial gland, pessary, prosthesis, suppository, and the like. Likewise with respect to the upper limit on the size of the device. In one specific embodiment, the dispenser can be of such size as to deliver 1 to 2 cc of drug formulation per day and to deliver a total of 5 to 10 cc of drug formulation over a 5 to 10 day period. With alternate choices of slower permeation membranes, the pump can deliver drug more slowly up to and in excess of 1 year. It is preferred that the construction of the canister and of the active agent release means be such that the osmotic driving pressure developed is at least ten times greater than the back pressure generated by the active agent formulation.

Thus, the invention provides, in an osmotic dispenser, a reliable means for releasing effective concentrations of active agent contained therein to the body of a living organism, or to any other fluid environment, at an osmotically controlled rate and over a prolonged period of time. In addition, prime advantages of the dispenser of the invention are that it is simple in construction and exhibits all of the practical advantages of the long-term continuous administration of various active agents both to humans, animals, and into other environments, and that the active agent contained therein will not exhibit the tendency to be leached therefrom.

While the invention has been described and illustrated with reference to certain preferred embodiments thereof, those skilled in the art will appreciate that various modifications, changes, omissions, and substitutions can be made without departing from the spirit of the invention. It is intended, therefore, that the invention be limited only by the scope of the following claims.