The present invention concerns apparatuses for transdermal delivery or transport of therapeutic agents, typically through iontophoresis. Herein the terms "iontophoresis" and "iontophoretic" are used to refer to methods and apparatus for transdermal delivery of therapeutic agents, whether charged or uncharged, by means of an applied electromotive force to an agent-containing reservoir. The particular therapeutic agent to be delivered may be completely charged (i.e., 100% ionized), completely uncharged, or partly charged and partly uncharged. The therapeutic agent or species may be delivered by electromigration, electroosmosis or a combination of the two. Electroosmosis has also been referred to as electrohydrokinesis, electro-convection, and electrically-induced osmosis. In general, electroosmosis of a therapeutic species into a tissue results from the migration of solvent, in which the species is contained, as a result of the application of electromotive force to the therapeutic species reservoir.
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 charged 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.
Iontophoretic devices for delivering ionized drugs through the skin have been known since the early 1900's. Deutsch U.S. Pat. No. 410,009 (1934) describes an iontophoretic device which overcame one of the disadvantages of such early devices, namely that the patient needed to be immobilized near a source of electric current. The Deutsch device was powered by a galvanic cell formed from the electrodes and the material containing the drug to be transdermally delivered. The galvanic cell produced the current necessary for iontophoretically delivering the drug. This device allowed the patient to move around during iontophoretic drug delivery and thus imposed substantially less interference with the patient's daily activities.
In presently known iontophoresis 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, agent, medicament, drug precursor or drug is delivered into the body via the skin 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 driven into the body is positively charged, then the positive electrode (the anode) will be the active electrode and the negative electrode (the cathode) will serve to complete the circuit. If the ionic substance to be delivered is negatively charged, then the cathodic electrode will be the active electrode and the anodic electrode will be the counter electrode.
Furthermore, existing iontophoresis devices generally require a reservoir or source of the beneficial agent or drug, preferably an ionized or ionizable species (or a precursor of such species) which is to be iontophoretically delivered or introduced into the body. Examples of such reservoirs or sources include a pouch as described in the previously mentioned Jacobsen U.S. Pat. No. 4,250,878, a pre-formed gel body as disclosed in Webster U.S. Pat. No. 4,382,529 and a generally conical or domed molding of U.S. Pat. No. 4,722,726 to Sanderson et al. Such drug reservoirs are connected to the anode or the cathode of an iontophoresis device to provide a fixed or renewable source of one or more desired species or agents.
Perhaps the most common use of iontophoresis today is in diagnosing cystic fibrosis by delivering pilocarpine transdermally. Iontophoretically delivered pilocarpine stimulates sweat production, the sweat is collected, and is analyzed for its chloride ion content. Chloride ion concentration in excess of certain limits suggests the possible presence of the disease.
A variety of methods for attaching an iontophoretic delivery device to the skin of a patient have been disclosed, including straps, adhesive overlays, and in-line ion-conducting adhesives. For example, Sibalis U.S. Pat. Nos. 4,557,723; 4,640.689; 4,622,031; 4,708,716; 4,713,050; and 4,878,892 describes transdermal iontophoretic drug applicators having a return electrode which is secured to the skin with a layer of an electrically conductive adhesive material (i.e., the layer designated 36 in FIG. 2 of U.S. Pat. No. 4,557,723). None of the above Sibalis patents disclose a specific composition for the skin-contacting, electrically conductive adhesive material.
PCT published application WO 90/09413 discloses ion-conducting skin contacting adhesives for securing iontophoretic drug delivery devices to the skin. The contact adhesives (eg., silicone adhesives) disclosed therein have a predominantly hydrophobic character which is modified by the addition of a hydrophilic, usually polymeric, material to the hydrophobic adhesive. The hydrophilic additive provides a plurality of water retaining pathways through the otherwise hydrophobic adhesive matrix. Drug ions or molecules are transported through the adhesive by way of these water retaining pathways by electromigration and/or electroosmosis. Thus, these adhesives can be used as "in-line" adhesive layers positioned between a drug-containing (donor) reservoir, or a salt-containing (counter) reservoir, and the skin.
In the devices of these patents, the electrical coupling of the various electronic components (e.g., resistors, current regulators, pulse generators, batteries, etc) has been accomplished using conventional electrical coupling means such as soldered electrical connections. Unfortunately, soldered electrical connections have a very poor tolerance for flexing. This is a serious disadvantage in devices such as iontophoretic drug delivery devices adapted to be worn on the skin for extended periods of time, e.g., as long as a week or more. When flexible (i.e., nonrigid) iontophoretic drug delivery devices having conventional soldered electrical connections are worn for such extended periods of time, there is a tendency for the electrical connections to break due to the flexing encountered during the patient's body movements. Breakage of an electrical connection can render the device completely inoperative.
Another approach described by Sibalis in U.S. Pat. No. 4,856,188 uses a flexible plastic sheet coated on one side with an electrically conductive coating to connect a battery of an iontophoresis apparatus to the electrodes. The opposite side of the sheet has an adhesive coating. The sheet is folded to permit the conductive coating to contact the battery terminal and the electrode. This approach tends to produce stress points at the folds which can cause the conductive coating to crack which can render the device completely inoperative.
Thus, there has been a need in the art for a means for electrically connecting or coupling electrical components in a flexible iontophoretic delivery device, which connections are not susceptible to breaking upon flexing of the device and which provide good electrical continuity at low cost.
More recently, there has been an effort to develop miniaturized iontophoretic drug delivery devices which are adapted to be worn on the skin unobtrusively under a patient's clothing. The electrical components in such miniaturized iontophoretic drug delivery devices are also preferably miniaturized and may be in the form of either microchips or small printed circuits. While printed circuits are desirable from a cost standpoint, there have been difficulties encountered in electrically connecting the printed circuit to the electrode assemblies containing the agent to be delivered. Specifically, printed electronic circuits are formed by printing or otherwise depositing electrically conductive pathways on a flexible substrate, usually in the form of a polymer sheet. Electronic components, e.g., batteries, resistors, pulse generators, capacitors etc, are then electrically connected, e.g., by soldering, to the printed or deposited electrically conductive pathways to form a complete circuit. Thus, in a typical case, both the printed electrically conductive pathways, as well as all of the electronic components electrically connected thereto, are located on one side of the flexible substrate. Because of the non-uniform height and cross-section presented by the various electrical components within the completed circuit, there have been difficulties encountered in laminating drug and/or electrolyte reservoirs to the side of the flexible circuit having the printed electrically conducted pathways and the electrical components mounted thereon.
One solution to this problem is to laminate the drug and electrolyte reservoirs to the opposite side of the flexible substrate. Unfortunately, this presents a problem in electrically connecting the drug and electrolyte reservoirs to the circuit. Thus, there has been a need in the art for a means for electrically connecting or coupling electrode assemblies, including drug and electrolyte reservoirs, of an iontophoretic delivery device to an electronic circuit having electrically conductive pathways and individual electronic components provided on one surface thereof, which connections are not susceptible to breaking upon flexing of the device and which provides good electrical continuity at low cost.