IONTOPHORETIC DELIVERY DEVICE

Abstract: An electrically powered iontophoretic delivery device is provided. The device utilizes electrodes composed of a preferably hydrophobic polymeric matrix. The matrix contains about 10 to 50 vol% of a material capable of absorbing a liquid solvent, typically water, to provide a plurality of ion conducting pathways through the matrix. The matrix also contains about 5 to 40 vol% of a chemical species which is able to undergo either oxidation or reduction during operation of the device. Preferably, the solvent absorbing material is a hydrophilic polymer such as polyvinylpyrrolidone. For the anodic electrode, the chemical species should be able to undergo oxidation and is preferably either silver or zinc. For the cathodic electrode, the chemical species should be able to undergo reduction and is preferably silver chloride or a reducible metal.

Description: IONTOPHORETIC DELIVERY DEVICE TECHNICAL FIELD This invention relates to a device for delivering an agent transdermally or transmucosally by iontophoresis. More particularly, this invention relates to an electrically powered iontophoretic delivery device having a polymer-based electrode. BACKGROUND ART Iontophoresis, according to Dorland's Illustrated Medical Dictionary, is defined to be "the introduction, by means of electric current, of ions of soluble salts into the tissues of the body for therapeutic purposes." Iontophoretic devices have been known since the early 1900's. British patent specification No. 410,009 (1934) describes an iontophoretic device which overcame one of the disadvantages of such early devices known to the art at that time, namely the requirement of a special low tension (low voltage) source of current which meant that the patient needed to be immobilized near such source. The device of that British specification was made by forming a galvanic cell from the electrodes and the material containing the medicament or drug to be delivered transdermally. The galvanic cell produced the current necessary for iontophoretically delivering the medicament. This ambulatory device thus permitted iontophoretic drug delivery with substantially less interference with the patient's daily activities. More recently, a number of United States patents have issued in the iontophoresis field, indicating a renewed interest in this mode of drug delivery. For example, U.S. Patent No. 3,991,755 issued to Vernon et al ; U.S. Patent No. 4,141,359 issued to Jacobsen et al ; U.S. Patent No. 4,398,545 issued to Wilson; and U.S. Patent No. 4,250,878 issued to Jacobsen disclose examples of iontophoretic devices and some applications thereof. The iontophoresis process has been found to be useful in the transder al administration of medicaments or drugs including " lidocaine hydrochloride, hydrocortisone, fluoride, penicillin, dexa ethasone sodium phosphate, insulin and many other drugs. Perhaps the most common use of iontophoresis is in diagnosing cystic fibrosis by delivering pilocarpine salts iontophoretically. The pilocarpine stimulates sweat production; the sweat is collected and analyzed for its chloride content to detect the presence of the disease. In presently known iontophoretic devices, at least two electrodes are used. Both of these electrodes are disposed so as to be in intimate electrical contact with some portion of the skin of the body. One electrode, called the active or donor electrode, is the electrode from which the ionic substance, medicament, drug precursor or drug is delivered into the body by iontophoresis. The other electrode, called the counter or return electrode, serves to close the electrical circuit through the body. In conjunction with the patient's skin contacted by the electrodes, the circuit is completed by connection of the electrodes to a source of electrical energy, e.g., a battery. For example, if the ionic substance to be delivered into the body is positively charged (i.e., a cation), then the anode will be the active electrode and the cathode will serve to complete the circuit. If the ionic substance to be delivered is negatively charged (i.e., an anion), then the cathode will be the active electrode and the anode will be the counter electrode. Alternatively, both the anode and cathode may be used to deliver drugs of opposite charge into the body. In such a case, both electrodes are considered to be active or donor electrodes. For example, the anode can deliver a positively charged ionic substance into the body while the cathode can deliver a negatively charged ionic substance into the body. It is also known that iontophoretic delivery devices can be used to deliver an uncharged drug or agent into the body. This is accomplished by a process called electroosmosis. Electroosmosis is the transdermal flux of a liquid solvent (e.g., the liquid solvent containing the uncharged drug or agent) which is induced by the presence of an electric field imposed across the skin by the donor electrode. As used herein, the terms "iontophoresis" and "iontophoretic" refer to (1) the delivery of charged " drugs or agents by electromigration, (2) the delivery of uncharged drugs or agents by the process of electroosmosis, (3) the delivery of cnarged drugs or agents by the combined processes of electromigration and electroosmosis, and/or (4) the delivery of a mixture of charged and uncharged drugs or agents by the combined processes of electromigration and electroosmosis. Furthermore, existing iontophoresis devices generally require a reservoir or source of the beneficial agent (which is preferably an ionized or ionizable agent or a precursor of such agent) to be iontophoretically delivered into the body. Examples of such reservoirs or sources of ionized or ionizable agents include a pouch as described in the previously mentioned Jacobsen U.S. Patent No. 4,250,878, or a pre-formed gel body as described in Webster U.S. Patent No. 4,383,529 and Ariura et al . U.S. Patent No. 4,474,570. Such drug reservoirs are electrically connected to the anode or the cathode of an iontophoresis device to provide a fixed or renewable source of one or more desired agents. More recently, iontophoretic delivery devices have been developed in which the donor and counter electrode assemblies have a "multi-laminate" construction. In these devices, the donor and counter electrode assemblies are each formed by multiple layers of (usually) polymeric matrices. For example, Parsi U.S. Patent 4,731.049 discloses a donor electrode assembly having hydrophilic polymer based electrolyte reservoir and drug reservoir layers, a skin-contacting hydrogel layer, and optionally one or more semipermeable membrane layers. Sibalis U.S. Patent No. 4,640.689 discloses in Figure 6 an iontophoretic delivery device having a donor electrode assembly comprised of a donor electrode (204), a first drug reservoir (202), a semipermeable membrane layer (200), a second drug reservoir (206), and a microporous skin-contacting membrane (22'). The electrode can be formed of a carbonized plastic, metal foil or other conductive films such as a metallized mylar film. In addition, Ariura et al , U.S. Patent 4,474,570 discloses a device wherein the electrode assemblies include a conductive resin film electrode layer, a hydrophilic gel reservoir layer, a current distribution and conducting layer and an insulating backing layer. Ariura et al disclose several different types of electrode layers including an aluminum foil electrode, a carbon fiber non-woven fabric electrode and a carbon-containing rubber film electrode. Others have suggested using biomedical electrodes having current distribution members composed of a rubber or other polymer matrix loaded with a conductive filler such as powdered metal. See for example, U.S. Patent No. 4,367,745. Such films however, have several disadvantages. First, as metal particle loading in a polymer matrix approaches about 65 vol%, the matrix begins to break down and becomes too brittle to be handled. Even at metal particle loadings of only about 50 to 60 vol%, the films produced are extremely rigid and do not conform well to non-planar surfaces. This is a particular disadvantage when designing an electrode adapted to be worn on the skin or a mucosal membrane. An iontophoretic electrode adapted to be worn on a body surface must have sufficient flexibility to contour itself to the natural shape of the body surface to which it is applied. The drug and electrolyte reservoir layers of iontophoretic delivery devices have been formed of hydrophilic polymers. See for example, Ariura et al , U.S. Patent 4,474,570; Webster U.S. Patent 4,383,529 and Sasaki U.S. Patent 4,764,164. There are several reasons for using hydrophilic polymers. First, water is the preferred solvent for ionizing many drug salts. Secondly, hydrophilic polymer components (i.e., the drug reservoir in the αonor electrode and the electrolyte reservoir in the counter electrode) can be hydrated while attached to the body by absorbing water from the skin (i.e., through transepidermal water loss or sweat) or from a ucosal membrane (e.g., by absorbing saliva in the case of oral mucosal membranes). Once hydrated, the device begins to deliver ionized agent to the body. This enables the drug reservoir to be manufactured in a dry state, giving the device a longer shelf life. The prior art has also recognized that certain electrode compositions are preferred from the standpoint of drug delivery efficiency and minimizing skin burns caused by pH extremes. For example, U.S. Patent Nos. 4,744,787; 4,747,819 and 4,752,285 all disclose iontophoretic electrodes which are either oxidized or reduced during operation of the device. Preferred electrode materials include a silver anodic electrode, which is used to deliver the chloride salt of a drug, and a silver/silver chloride cathodic (return) electrode. Silver ions generated at the anode combine with the drug counter ion (i.e., chloride ions) to produce an insoluble silver chloride precipitate. This reduces competition between the drug ions and the silver ions for delivery into the body and increases the efficiency of the device. DISCLOSURE OF THE INVENTION It is an object of this invention to provide an improved electrode for an iontophoretic delivery device. This and other objects are met by an electrically powered iontophoretic delivery device including a donor electrode assembly, a counter electrode assembly and a source of electrical cower adapted to be electrically connected to the donor and counter electrode assemblies. At least one of the donor and counter electrode assemblies includes an agent reservoir containing an agent, the, agent reservoir adapted to be placed in agent transmitting relation with a body surface, and an electroαe adapted to be electrically connected to the source of electrical power and to the agent reservoir. The electrode comprises a polymeric matrix containing about 5 to 40 vol of a chemical species which is able to undergo either oxidation or reduction during operation of the device and about 10 to 50 vol% of an agent capable of absorbing a liquid solvent (e.g., water) and thereby forming a plurality of ion-conducting pathways through the matrix. When the electrode is an anode, the chemical species is able to undergo oxidation and is preferably an oxidizable metal such as silver or zinc. When the electrode is a cathode, the chemical species is able to undergo reduction during operation of the device, and is preferably silver chloride or a reducible metal. The solvent-absorbing agent is preferably formed of a hydrophilic polymer which is substantially insoluble in the solvent. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a schematic view of an iontophoretic drug delivery device according to the present invention; and Figure 2 is a schematic view of another embodiment of an iontophoretic delivery device according to the present invention. MODES FOR CARRYING OUT THE INVENTION Figure 1 is a schematic view of an iontophoretic delivery device 10 for delivering a beneficial agent through a body surface 22. Body surface 22 is typically intact skin or a mucosal membrane. Iontophoretic delivery device 10 includes a donor electrode assembly 8, a counter electrode assembly 9, an electrical power source 27 (e.g., a battery) and an optional control circuit 19. The donor electrode assembly 8 includes a donor electrode 11 and an agent reservoir 15. The agent reservoir 15 contains the beneficial agent to be iontophoretically delivered by device 10. The donor electrode assembly 8 is adhered to the body surface 22 by means of an ion-conducting adhesive layer 17. Iontophoretic delivery device 10 includes a counter electrode assembly 9 which is placed on the body surface 22 at a location spaced apart from electrode assembly 8. Counter electrode assembly 9 includes a counter electrode 12 and an electrolyte reservoir 16. Counter electrode assembly 9 is adhered to the body surface 22 by means of an ion-conducting adhesive layer 18. The donor and counter electrode assemblies 8 and 9 normally include a strippable release liner, not shown, which is removed prior to application of electrode assemblies 8 and 9 to body surface 22. The electrolyte reservoir 16 contains a pharmacologically acceptable salt. Suitable electrolytes for reservoir 16 include sodium chloride, alkaline salts, chlorides, sulfates, nitrates, carbonates, phosphates, and organic salts such as ascorbates, citrates, acetates and mixtures thereof. Reservoir 16 may also contain a buffering agent. Sodium chloride is a suitable electrolyte when the counter electrode 12 is the cathode and is composed of silver/silver chloride, optionally with a sodium phosphate buffer. When the device 10 is in storage, no current flows because the device forms an open circuit. When the device 10 is placed on the skin or mucosal membrane of a patient and reservoirs 15 and 16, layers 17 and 18, and electrodes 11 and 12 become sufficiently hydrated to allow conduction of ions therethrough, the circuit oetween the electrodes is closed and the power source begins to deliver current through the device and through the body of the patient. Electrical current flowing through the conductive portions of the device 10 (i.e., those portions used to connect the power source 27 to the electrodes 11 and 12) is carried by electrons (electronic conduction), while current flowing through the hydrated portions of the device 10 (e.g., the electrodes 11 and 12, the agent reservoir 15, the electrolyte reservoir 16 and the ion-conducting adhesive layers 17 and 18) is carried by ions (ionic conduction). In order for current to flow through the device, it is necessary for electrical charge to be transferred from power source 27 to chemical species in solution in electrodes 11 and 12, respectively, by means of oxidation and reduction charge transfer reactions within the electrodes 11 and 12. Electrodes 11 and 12 are each comprised of a hydrophobic polymeric matrix. The matrix contains about 10 to 50 vol% of an agent which is capable of absorbing a liquid solvent, typically an aqueous solvent, and thereby forming ion-conducting pathways through the matrix. The matrix also contains about 5 to 40 vol% of a chemical species which is able to undergo either oxidation or reduction during operation of the device. The polymer used as the matrix for electrodes 11 and 12 is preferably selected from hydrophobic polymers which can be suitably mixed with the solvent- absorbing agent and the chemical species able to undergo oxidation or reduction. As used herein, a hydrophobic polymer is any polymer having an equilibrium water content of less than 20 wt%, preferably less than about 15 wt% and most preferably less than about 10 wt% after prolonged exposure to an atmosphere having a relative humidity of over about 90%. Examples of suitable polymers for use as the matrix of electrodes 11 and 12 include, without limitation, polyalkenes, polyisoprenes, rubbers such as polyisobutylene, ethylene vinyl acetate copoly ers, polyamides, polyurethanes, polyvinylchloride, modified cellulosic polymers, highly cross-linked polyethylene oxides and mixtures thereof. Preferred hydrophobic polymeric matrices for electrodes 11 and 12 include polyisobutylenes, copoly ers of ethylene vinyl acetate and mixtures thereof. The polymeric matrix of electrodes 11 and 12 contains about 5 to 40 vol%, preferably about 15 to 30 vol%, and most preferably about 20 to 25 vol% of a chemical species which is able to undergo either oxidation or reduction during operation of the device. As mentioned above, as electrical current flows through device 10, oxidation or reduction of some chemical species takes place within at least one of the electrodes 11 and 12. Most typically, oxidation of an oxidizable chemical species takes place within the anode while reduction of a reducible chemical species takes place within the cathode. Although a variety of electrochemical reactions can be utilized, the present invention utilizes a class of charge transfer reactions whereby a portion of at least one of the electrodes 11 and 12 participates in a charge transferring chemical reaction, i.e., a material in at least one of the electrodes 11 and 12 is consumed or generated. This is accomplished through oxidation and/or reduction reactions occurring within the electrodes. Examples of preferred oxidation/reduction reactions include the following: Ag = Ag + + e " Zn = Zn *2 + 2e " Cu » Cu +2 + 2e ~ Ag + CT s AgCl + e " Zn + 2C1 " = ZnCl 2 + 2e ~ where the forward reaction is the oxidation reaction taking place in the anodic electrode and the reverse reaction is the reduction reaction taking place in the cathodic electrode. Other standard electrochemical reactions and their respective reduction potentials are well known in the art. See the CRC Handbook of Chemistry and Physics, pp D 151-58, 67th edition (1986-1987). If the electrode is to be used as an anode, the chemical species should be able to undergo oxidation during operation of the device. Suitable chemical species able to undergo oxidation include electrically conductive metals such as silver, zinc, copper, nickel, tin, lead, iron and chromium. Other oxidizable species are listed in the CRC Handbook of Chemistry and Physics. 57th edition, D-141 to D-146. Preferred chemical species able to undergo oxidation are electrically conductive metals, preferably in the form of powders. Most preferred are silver and zinc powders. Although non-conductive oxidizable chemical species can also be used, they require an additional electrically conductive filler in the polymeric matrix. Suitable conductive fillers include carbon or graphite fibers, carbon or graphite powders and powdered metals. If the electrode is to be used as a cathode, the chemical species should be able to undergo reduction during operation of the device. Suitable chemical species which are able to undergo reduction include silver chloride, silver bromide, silver hexacyanoferrate, cupric sulfate, cupric chloride and other reducible species listed in the CRC Handbook of Chemistry and Physics. 57th edition, D-141 to D-146. Preferably, the reducible chemical species is also electrically conductive. Of these, silver chloride is most preferred. Although non-conductive reducible chemical species (e.g., cupric sulfate and cupric chloride) can also be used, they require an additional electrically conductive filler in the polymeric matrix. Suitable conductive fillers include carbon or graphite fibers, carbon or graphite powders and powdered metals. Electrodes 11 and 12, once hydrated, each have a plurality of liquid solvent-containing pathways running therethrough. These pathways can be formed by mixing a sufficient quantity, generally about 10 to 50 vol%, preferably about 20 to 35 vol% and most preferably about 25 to 30 vol%, of an agent capable of absorbing a solvent, such as water, throughout the matrices of electrodes 11 and 12. Electrodes 11 and 12 can be manufactured in a non- hydrated condition, thereby giving the electrodes and the device a longer and more stable shelf life. Water, and/or another liquid solvent, can then be applied to the electrodes at the time of use. The solvent absorbing agent absorbs the liquid solvent (e.g., water) thereby forming ion-conducting pathways through the matrices of electrodes 11 and 12. In certain situations wherein the agent reservoir 15 and the electrolyte reservoir 16 are also manufactured in a dry (e.g., non-hydrated) state, these same pathways can be used to conduct liquid solvent into the non- hydrated drug and/or electrolyte reservoirs and/or ion-conducting adhesive layers in order to hydrate these additional layers and place the device in an operational (e.g., hydrated) condition. The agent which is capable of absorbing a liquid solvent and thereby forming ion-conducting pathways through electrodes 11 and 12 are typically water absorbent materials since the preferred medium for conducting transdermal iontophoretic drug delivery is aqueous based. Preferred solvent-absorbing agents are hydrophilic polymers which are substantially water insoluble. As used herein, a hydrophilic polymer is a polymer having an equilibrium water content of at least 20 wt%, preferably at least about 30 wt% and most preferably at least about 40 wt% after prolonged exposure to an atmosphere having a relative humidity of over about 90%. Examples of suitable hydrophilic water insoluble polymers include polyvinylpyrrolidones, hydrogels such as polyethylene oxides, Polyox ® , Polyox ® blended with polyacrylic acid or Carbopol ® , Carbowaxes ® , highly crystallized polyvinyl alcohols, cellulose derivatives such as hydroxypropyl methyl cellulose, hydroxypropyl cellulose, mixtures of highly crystallized polyvinyl alcohols and hydroxypropyl methyl cellulose, insoluble starch derivatives, such as starch-graft poly(Na acrylate co-acrylamide) polymers sold jnder the tradename Waterlock® by Grain Processing Corp., Muscatine, IA, and the like, along with blends thereof. Figure 2 illustrates another iontophoretic delivery device designated by the numeral 20. Like device 10, device 20 also contains an electrical power source 27 (e.g., a battery) and an optional control circuit 19. However, in device 20 the donor electrode assembly 8 and the counter electrode assembly 9 are physically attached to an insulator 26 and form a single self- contained unit. Insulator 26 prevents the electrode assemblies 8 and 9 from short circuiting by preventing electrical and/or ion transport between the electrode assemblies 8 and 9. Insulator 26 is preferably formed of a hydrophobic non-conducting polymeric material which is impermeable to both the passage of ions and water. A preferred insulating material is a nonporous ethylene vinyl acetate copolymer. Alternatively, both the donor electrode assembly 8 and the counter electrode assembly 9 may be used to iontophoretically deliver different beneficial agents through body surface 22. For example, positive agent ions can be delivered through body surface 22 from the anodic electrode assembly, while negative agent ions can be delivered from the cathodic electrode assembly. Alternatively, neutral drugs can be introduced from either electrode assembly by electroosmosis. As an alternative to the side-by-side alignment of the donor electrode assembly 8, the insulator 26 and the counter electrode assembly 9 shown in Figure 2, the electrode assemblies can be concentrically aligned with the counter electrode assembly positioned centrally and surrounded by the insulator 26 and the donor electrode assembly. The electrode assemblies can, if desired, be reversed with the counter electrode assembly surrounding the centrally positioned donor electrode assembly. The concentric alignment of the electrode assemblies can be circular, elliptical, rectangular or any of a variety of geometric configurations. Power source 27 is typically one or more batteries. As an alternative to a battery, device 10 can be powered by a galvanic couple formed by the donor electrode 11 and counter electrode 12 being composed of dissimilar electrochemical couples and being placed in electrical contact with one other. Typical materials for delivering a cationic agent into the body include a zinc donor electrode 11 and a silver/silver chloride counter electrode 12. A Zn-Ag/AgCl galvanic couple provides an electrical potential of about 1 volt. The agent and electrolyte reservoirs 15 and 16 can be formed by blending the desired agent, drug, electrolyte or other component(s), with the polymer by melt blending, solvent casting or extrusion, for example. The drug and/or electrolyte loading in the polymer matrix is generally about 10 to 60 wt%, although drug and/or electrolyte loadings outside this range may also be used. Suitable polymers for use as the matrix of reservoirs 15 and 16 include, without limitation, hydrophobic polymers such as polyethylene, polypropylene, polyisoprenes and polyalkenes, rubbers such as polyisobutylene, copoly ers such as Kraton®, polyvinylacetate, ethylene vinyl acetate copolymers, polyamides including nylons, polyurethanes, polyvinylchloride, cellulose acetate, cellulose acetate butyrate, ethylcellulose, cellulose acetate, and blends thereof; and hydrophilic polymers such as hydrogels, polyvinylpyrrolidones, polyethylene oxides, Polyox ® , Polyox ® blended with polyacrylic acid or Carbopol ® , cellulose derivatives such as hydroxypropyl methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, pectin, starch, guar gum, locust bean gum, and the like, along with blends thereof. The adhesive properties of the reservoirs 15 and 16 may be enhanced by adding a resinous tackifier. This is especially important when using a non-tacky polymeric matrix. Examples of suitable tackifiers include products sold under the trademarks Staybelite Ester #5 and #10, Regal-Rez and Piccotac, all sold by Hercules, Inc. of Wilmington, DE. Additionally, the matrix may contain a rheological agent, suitable examples of which include mineral oil and silica. In addition to the drug and electrolyte, the reservoirs 15 and 16 may also contain other conventional materials such as uffers, dyes, pigments, inert fillers, and other excipients. A control circuit 19 is optionally provided. Control circuit 19 may take the form of an on-off switch for "on-demand" drug delivery (e.g., on-demand delivery of an analgesic for pain control), a timer, a fixed or variable electrical resistor, a controller which automatically turns the device on and off at some desired periodicity to match the natural or circadian patterns of the body, or other more sophisticated electronic control devices known in the art. For example, it may be desirable to deliver a predetermined constant level of current from device 10 since a constant current level ensures that the drug or agent is delivered through the skin at a constant rate. The current level can be controlled by a variety of known means, for example, a resistor or a field effect transistor or a current limiting diode. Control circuit 19 may also include a microchip which could be programmed to control the dosage of beneficial agent, or even to respond to sensor signals in order to regulate the dosage to maintain a predetermined dosage regimen. A relatively simple controller or microprocessor can control the current as a function of time, and if desired, generate complex current waveforms such as pulses or sinusoidal waves. In addition, the control circuit 19 may employ a bio-feedback system which monitors a biosignal, provides an assessment of the therapy, and adjusts the drug delivery accordingly. A typical example is the monitoring of the blood sugar level for controlled administration of insulin to a diabetic patient. As used herein, the expression "agent" can mean a drug or other beneficial therapeutic agent when referring to the donor electrode assembly and/or an electrolyte salt when referring to the counter electrode assembly. The expressions "drug" and "therapeutic agent" are used interchangeably and are intended to have their broadest interpretation as any therapeutically active substance which is delivered to a living organism to produce a desired, usually beneficial, effect. In general, this includes therapeutic agents in all of the major therapeutic areas including, but not limited to, anti-infectives such as antibiotics and antiviral agents, analgesics and analgesic combinations, anesthetics, anorexics, antiarthritics, antiasthmatic agents, anticonvulsants, antidepressants, antidiabetic agents, antidiarrheals, antihistamines, anti-inflammatory agents, antimigraine preparations, antimotion sickness preparations, antinauseants, antineoplastics, antiparkinsonism drugs, antipruritics, antipsychotics, antipyretics, antispasmodics, including gastrointestinal and urinary, anticholinergics, sympatho imetrics, xanthine derivatives, cardiovascular preparations including calcium channel blockers, beta-blockers, antiarryth ics, antihypertensives, diuretics, vasodilators, including general, coronary, peripheral and cerebral, central nervous system stimulants, cough and cold preparations, decongestants, diagnostics, hormones, hypnotics, immunosuppressives, muscle relaxants, parasympatholytics, parasympathomimetrics, proteins, peptides, psychostimulants, sedatives and tranquil izers. The invention is also useful in the controlled delivery or peptides, polypeptides, proteins and other macromolecules. These macromolecular substances typically have a molecular weight of at east about 300 daltons, and more typically a molecular weight in the range of about 300 to 40,000 daltons. Specific examples of peptides and proteins in this size range include, without limitation, LHRH, LHRH analogs such as buserelin, gonadorelin. naphrelin and leuprolide, GHRH, insulin, heparin, calcitonin, endorphin, TRH, NT-36 (chemical name: N=[[(s)-4-oxo-2- azetidinyl]carbonyl]-L-histidyl-L-prolinamide), liprecin, pituitary hormones (e.g., HGH, HMG, HCG, desmopressin acetate, etc.), follicle luteoids, αANF, growth factor releasing factor (GFRF), £MSH, somatostatin, bradykinin, somatotropin, platelet- derived growth factor, asparaginase, bleomycin sulfate, nymopapain, cholecystokinin, chorionic gonadotropin, corticotropin (ACTH), erythropoietin, epoprostenol (platelet aggregation inhibitor), glucagon, hyaluronidase, interferon, interleukin-2, enotropins (urofollitropin (FSH) and LH), oxytocin, streptokinase, tissue plasminogen activator, urokinase, vasopressin, ACTH analogs, ANP, ANP clearance inhibitors, angiotensin II antagonists, antidiuretic hormone agonists, antidiuretic hormone antagonists, bradykinin antagonists, CD4, ceredase, CSF's, enkephalins, FAB fragments, IgE peptide suppressors, IGF-1, neurotrophic factors, parathyroid hormone and agonists, parathyroid hormone antagonists, prostaglandin antagonists, pentigetide, protein C, protein S, renin inhibitors, thy osin alpha-1, thro bolytics, TNF, vaccines, vasopressin antagonist analogs, alpha-1 anti-trypsin (recombinant) . It is most preferable to use a water soluble salt of the drug or agent to be delivered. The combined skin-contacting areas of electrode assemblies 8 and 9 can vary from less than 1 cm 2 to greater than 200 cm 2 . The average device 10 however, will have electrode assemblies with a combined skin-contacting area within the range of about 5 to 50 cm-. As an alternative to the ion-conducting adhesive layers 17 and 18 shown in Figures 1 and 2, the iontophoretic delivery devices 10 and 20 may be adhered to the skin using an adhesive overlay. Any of the conventional adhesive overlays used to secure passive transdermal delivery devices to the skin may be used. Another alternative to the ion-conducting adhesive layers 17 and 18 is a peripheral adhesive layer surrounding reservoir 15 and/or 16, allowing reservoir 15 and/or 16 to have a surface in direct contact with the patient's skin. Having thus generally described our invention, the following examples will illustrate preferred embodiments thereof. EXAMPLE I An anodic electrode was made by mixing powdered silver and cross-linked polyvinylpyrrolidone into a polyisobutylene matrix. First, 11.4 g of polyisobutylene (PIB) having a molecular weight of 1,200,000 (sold by Exxon Corp. of Irving, Texas) were added to a 50 cm 3 Brabender mixer (Brabender Instruments, Inc., South Hackensack, NJ). The mixer bowl was preheated to 80'C and the blade speed was set at 30 rp . Then, 11.4 g of PIB having a molecular weight of 35,000 (sold by Exxon Corp. of Irving, Texas) was slowly added to the mixer. The PIB's were mixed for about five minutes until they were well mixed. Thereafter, 11.3 g of polyvinylpyrrolidone, sold by GAF Corp. of Wayne, NJ and having a degree of cross-linking of 10%, were slowly added into the mixer over a period of about five minutes. Thereafter, 118.1 g of silver powder having an average particle size of about 8 microns were slowly added to the mixer over a period of about 15 minutes. Mixing was continued for an additional 30 minutes. Five batches of the material (about 250 cm 3 ) were then loaded into a Brabender extruder having a 0.75 inch screw. The temperature at the screw was about llO'C. An adjustable sheet extrusion die having a die opening with a width of 4 inches and a height adjustable between 1 and 40 mils was mounted at the end of the extruder. The temperature of the film at the die opening was 110°C. After extrusion, the film was passed between opposing calender rolls heated to about 105 * C. The calendered film had a thickness of 6 mils. The film exhibited a voltage drop of less than 0.5 volts when a_ ccuurrrreenntt ddeeinsity of 100 μA/cm 2 of direct current was passed through the film. Experiments were conducted to evaluate the electrochemical performance of the anodic film electrode in comparison with the electrochemical performance of an electrode composed of pure silver. The apparatus used to measure the electrochemical performance of the electrodes included a cell containing an electrolyte solution and means for connecting an anode and a cathode within the cell. The electrodes of the cell are connected in series with a potentiostat which is set to supply the necessary voltage to maintain a constant current level of 100 μA/cm 2 through the circuit. Normal saline was used as the liquid electrolyte solution in the cell. The cell voltage required to pass 100 μA/cm 2 of current was monitored as a function of time for a period of 24 hours. A control experiment used pure silver as the anode, a silver chloride cathode and the saline electrolyte. The cell voltage was monitored and recorded over a 24 hour test period. A duplicate experiment was run with the Ag/PVP/PIB anodic film electrode. The cathodic electrode in both the control and actual experiments was composed of AgCl . Over the entire 24 hour test period, the measured cell voltage of the anodic film electrode was less than 0.3 volts greater than the measured cell voltage of the pure silver electrode. This small increase in the measured cell voltage is considered to be acceptable for an electrode used in a transdermal iontophoretic delivery device. In general, electrode materials requiring the least amount of additional voltage to deliver the required amount of electrical current are most preferred. Accordingly, the anodic film electrode of the present invention exhibits an electrochemical performance that is only marginally below the performance of a pure silver anodic electrode. EXAMPLE II A cathodic electrode was made by mixing silver chloride powder and cross-linked polyvinylpyrrolidone into a polyisobutylene matrix. First, 11.4 g of polyisobutylene (PIB) having a molecular weight of 1,200,000 were added to a 50 cm 3 Brabender mixer. The mixer bowl was preheated to 80 * C and the blade speed was set at 30 rpm. Thereafter, 11.4 g of PIB having a molecular weight of 35,000 was slowly added to the mixer. The PIB's were mixed for about five minutes until they were well mixed. Thereafter, 11.3 g of cross-linked polyvinylpyrrolidone (PVP) were slowly added into the mixer over a period of about five minutes. Thereafter, 62.6 g of granular silver chloride having a particle size of less than 100 microns were slowly added to the mixer over a period of about five minutes. Thereafter, the blade speed was maintained at 30 rpm for an additional 30 minutes of mixing. Five batches of the material (about 250 cm 3 ) were then loaded into the same extruder/die combination described in Example I. The temperature at the screw was about 105 * C. The temperature of the film at the die opening was about 130'C. After extrusion, the film was passed between opposing calender rolls heated to about 160"C. The calendered film had a thickness of 6 mils. The cathodic film exhibited a voltage drop of less than 0.5 volts when a current density of 100 /_A/cm 2 of direct current was passed through the film. Experiments were conducted to evaluate the electrochemical performance of the AgCl/PVP/PIB cathodic film electrode in comparison with the electrochemical performance of an electrode composed of sintered silver chloride, using the same apparatus and procedures described in Example I. The anodic electrode in both the control and actual experiments was composed of pure silver. Over the entire 24 hour test period, the measured cell voltage of the cathodic film electrode was less than 0.3 volts greater than the measured cell voltage of the sintered silver chloride electrode. This small increase in the measured cell voltage is considered to be acceptable for an electrode used in a transdermal iontophoretic delivery device. In general, electrode materials requiring the least amount of additional voltage to deliver the required amount of electrical current are most preferred. Accordingly, the cathodic film electrode of the present invention exhibits an electrochemical performance that is only marginally below the performance of a sintered silver chloride cathodic electrode. Having thus generally described our invention and described in detail certain preferred embodiments thereof, it will be readily apparent that various modifications to the invention may be made by workers skilled in the art without departing from the scope of this invention and which is limited only by the following claims.

Claims: CLAIMS What is claimed is: 1. An electrically powered iontophoretic delivery device including a donor electrode assembly, a counter electrode assembly and a source of electrical power adapted to be electrically connected to the donor electrode assembly and the counter electrode assembly, at least one of the electrode assemblies including an agent reservoir containing an agent, the agent reservoir adapted to be placed in agent transmitting relation with a body surface; and an electrode adapted to be electrically connected to the source of electrical power and to the agent reservoir; wherein the electrode comprises: a hydrophobic polymeric matrix; about 10 to 50 vol% of an agent which can absorb a liquid solvent thereby forming a plurality of ion-conducting pathways through the matrix; and about 5 to 40 vol% of a chemical species able to undergo oxidation or reduction during operation of the device. 2. The device of claim 1, wherein the electrode is an anode and the chemical species is an electrically conductive metal able to undergo oxidation during operation of the device. 3. The device of claim 2, wherein the metal is selected from the group consisting of silver and zinc. 4. The device of claim 1, wherein the electrode is a cathode and the chemical species is able to undergo reduction during operation of the device. 5. The device of claim 4, wherein the chemical species able to undergo reduction is an electrically conductive salt selected from the group consisting of AgCl , AgBr, and Ag 4 Fe(CN) e . 6. The device of claim 4, wherein the chemical species able to undergo reduction is electrically non-conductive and the matrix also contains an electrically conductive filler. 7. The device of claim 6, wherein the electrically non- conductive reducible species is selected from the group consisting of CuCl 2 and CuS0 4 and the conductive filler is comprised of a metal or carbon. 8. The device of claim 1, wherein the solvent-absorbing agent is substantially insoluble in the solvent. 9. The device of claim 1, wherein the solvent absorbing agent comprises a water-insoluble hydrophilic polymer. 10. The device of claim 9, wherein the hydrophilic polymer is selected from the group consisting of ethylene vinyl acetate copolymers and polyisobutylenes. 11. The device of claim 1, wherein the hydrophobic polymeric matrix is selected from the group consisting of ethylene vinyl acetate copolymers, polyalkylenes, polyisoprenes, rubbers including polyisobutylenes, polyamides, polyurethanes, polyvinylchlorides, modified cellulosic polymers and mixtures thereof. 12. The device of claim 1, wherein the hydrophobic polymer matrix is in the form of a film. 13. The device of claim 1, wherein the counter electrode assembly includes a counter electrode adapted to be electrically connected to the source of electrical power and an electrolyte reservoir adapted to be placed in electrolyte transmitting relation with the body surface, the counter electrode being in electrical contact with the electrolyte reservoir; wherein the counter electrode comprises: a hydrophobic polymeric matrix; about 10 to 50 vol% of an agent which can absorb a liquid solvent thereby forming a plurality of ion-conducting pathways through the matrix; and about 5 to 40 vol% of a chemical species able to undergo oxidation or reduction during operation of the device. 14. The device of claim 13, wherein the electrolyte reservoir is a polymeric matrix comprised of about 10 to 60 wt% of a hydrophilic polymer about 10 to 60 wt% of a hydrophobic polymer and up to about 50 wt% of the electrolyte. 15. The device of claim 1, wherein the donor electrode assembly includes a donor electrode adapted to be electrically connected to the source of electrical power and a drug reservoir adapted to be placed in drug transmitting relation with the body surface, the donor electrode having a surface which is in contact with the drug reservoir. 16. The device of claim 15, wherein the drug reservoir is a polymeric matrix comprised of about 10 to 60 wt% of a hydrophilic polymer, about 10 to 60 wt% of a hydrophobic polymer and up to about 50 wt% of the drug. 17. The " device of claim 1, wherein the power source comprises a battery. 18. The device of claim 1, wherein the agent comprises a drug. 19. The device of claim 18, wherein the drug is a water soluble drug salt. 20. The device of claim 1, wherein the agent comprises an electrolyte. 21. The device of claim 20, wherein the electrolyte comprises a water soluble electrolyte salt.

Inventors: GYORY J RICHARD, LANDRAU FELIX ANTONIO, MYERS ROBERT M, STAHL MARK G, GYORY, J., RICHARD, LANDRAU, FELIX, ANTONIO, MYERS, ROBERT, M., STAHL, MARK, G.
Applicants: ALZA CORP, ALZA CORPORATION
Application year: 1991
Main classification: A61N1
IPC codes: A61N1