Method of Forming Adhesive Patch for Applying Medication to the Skin

This invention relates to an improved method of forming an adhesive patch for applying medication to the skin.

Several kinds of patch devices have been used in the past for applying medication to the skin. For example, U.S. Pat. No. 4,675,009 describes a drug dispensing device for transdermal delivery of medication in which a natural or synthetic polysaccharide or synthetic polymer functions as a non-biodegradable adhesive reservoir. These patches, while very good, are so thick and cumbersome that users complain of their appearance and the discomfort associated with their use. Another deficiency is found in analgesic patch products that contain a rubber sheet backing which occludes the skin, making moisture evaporation virtually impossible.

One important object of the present invention is to provide a non-occlusive analgesic patch, i.e., one which will enable moisture vapor on the surface of the skin to evaporate through the patch so as to prevent the undesired accumulation of moisture which, if it occurred, could cause the patch to fall off or even facilitate the growth of bacteria beneath the patch.

Another objective of the present invention is to provide a much lighter, more flexible and less obtrusive patch while still providing excellent sustained release properties during eight hours or more of use.

Another more specific object is to find a way to enable the backing of the adhesive tape itself to serve as a reservoir for the sustained release of a medication to be applied topically into the skin.

Still another more specific object is to unify a porous backing and a hydrophilic pressure-sensitive hydrocolloidal dispersion which serves as a reservoir for medication so as to provide sustained release of the medication while reducing the thickness and bulk of the patch and improving its flexibility.

A further more specific object of the present invention is to provide a more comfortable and less obtrusive topical analgesic patch for the temporary relief of pain including arthritis pain, backaches as well as muscular aches and strains.

Yet another object is to provide an improved method of combining the porous backing and the hydrocolloidal medication-containing pressure-sensitive adhesive reservoir during manufacture.

These and other more detailed and specific objects of the present invention will be better understood by reference to the following figures and detailed description which illustrate by way of example but a few of the various forms of the invention within the scope of the appended claims.

Briefly, the present invention provides a non-occlusive medication patch to be applied to the skin. It includes a porous self-supporting backing layer to give the patch the required integrity and strength by acting as a supporting framework for other components, and a flexible hydrophilic pressure-sensitive adhesive reservoir comprising a hydrocolloidal gel for the sustained release of medication to be absorbed topically through the skin into the body of a patient. The reservoir has two portions: first, an external coating layer with an exposed lower skin-contacting surface that forms a pressure-sensitive bond with the skin, and second, an upper internal portion which infiltrates the porous backing and becomes solidified therein after being applied so that the reservoir and the backing are unified, enabling the backing itself to act as a storage location for the medication-containing reservoir. In this way, the medication within the reservoir migrates over time from within the backing through the lower coating layer and passes through the skin to provide sustained release of the medication into the body of a patient.

The reservoir comprises a hydrocolloidal dispersion of a natural or synthetic gel-forming polymer, a hydrophilic adhesive, a hydrophilic humectant and a biomedically active medication, i.e., a medicament, dispersed throughout the reservoir including both the external portion and the internal portion that infiltrates the porous backing.

The invention provides a comfortable, highly flexible patch that is thinner than prior patches, conforms to the body contours, is better tolerated by patients, and is considered by patients to be more unobtrusive. The invention provides outstanding results as a non-occlusive analgesic patch that can be adhered to the skin to release an analgesic for the relief of pain including arthritis pain, backache as well as muscular aches and strains. In such an application, the analgesic comprises trolamine salicylate, menthol salicylate, menthol, camphor, eucalyptus oil or spearmint oil, or a combination thereof.

The invention will be better understood by reference to the following specification and accompanying drawings.

FIG. 1 is a perspective diagrammatic view illustrating a preferred method of forming products in accordance with the invention;

FIG. 2 is a perspective view of the improved medication patch applied to the body;

FIG. 3 is a plan view showing the medication patch packaged within in a pouch used as a shipping package;

FIG. 4 is a cross-sectional view of the medication patch taken on line 4--4 of FIG. 3 with a portion of the liner sheet partially removed; and

FIG. 5 is a greatly enlarged microscopic view of the medication patch and liner sheet taken on line 5--5 of FIG. 4.

Refer now to FIG. 1 which illustrates diagrammatically the production of medication-applying patches in accordance with the invention. The backing sheet 10 is unwound continuously from a supply roll 12, passes upwardly in the figure over an idler roll 14 and then travels horizontally beneath a continuous processing mixer 16 where freshly prepared fluid hydrogel material at 20 is applied to the upper surface of the backing sheet 10.

The backing 10 is a porous self-supporting sheet of water insoluble polymeric material that provides strength and integrity for the adhesive patch as well as acting as a substrate for receiving and retaining a portion of the liquid hydrogel as will be described below.

One preferred backing sheet 10 is a lightweight, pliable strip composed, for example, from a nonwoven fabric which consists of polymeric fibers such as polyester, cotton or cellulose fibers bonded together with a sizing resin. The backing sheet 10 should be nonirritating to human skin. If desired, the backing sheet 10 can be coated on its back surface with a release coating such as a silicone release coating as described in U.S. Pat. No. 4,696,854 which is incorporated herein by reference. One suitable release coating is a 100% solids electron beam curable silicone such as Tego.RTM. silicone Resin Acrylates/RC-Series RC 705 and RC 726 by Goldschmidt Chemical Corporation of Hopewell, Va. The preferred backing sheet 10 is a porous polymeric water insoluble nonwoven fibrous fabric. A suitable sizing material for bonding the fibers together is a latex resin.

The backing sheet 10 can comprise other stable, water insoluble flexible sheet materials. One preferred backing comprises a 5.5 mil. strip of nonwoven fabric formed from a mixture of cellulose fibers derived from wood pulp and polyester fibers. The fibers are assembled loosely into the backing to maintain porosity. A unifying or sizing resin is applied to hold the fibers together. The sizing resin can comprise a nonirritating resin applied as a latex emulsion. One example is Hycar.RTM. 26477, an acrylate resin emulsion adhesive produced by B.F. Goodrich Co. of Brecksville, Ohio. Another suitable backing sheet is a nonwoven fabric comprising a wetlay cellulose and polyester nonwoven fabric containing as a sizing an acrylic latex emulsion resin, e.g., product number N7601 by Dexter Corporation of Windsor Locks, Conn.

In another embodiment of the invention, the backing sheet 10 comprises a porous woven 5 mil. acetate polymer cloth sometimes known as "silk cloth." Another form of backing sheet 10 is an open-cell plastic foam strip of low density polyethylene or polyvinyl acetate resin. Other backing sheets that can be used include woven cotton cloth or other cloth formed from a synthetic polymer. Suitable synthetic cloths include nylon, polyester, polyacetate. When the backing sheet 10 is a woven cloth, no sizing resin is needed. The backing sheet 10 is pervious to air so that the patch is non-occlusive to the skin.

The porosity of the backing sheet 10 is important because it provides openings for receiving the hydrocolloidal medication-containing reservoir and it helps to assure that the patch is non-occlusive to the skin. The infusion of the pressure-sensitive hydrocolloidal medication-containing reservoir into the backing sheet 10 is accomplished by controlling manufacturing parameters so as to keep the hydrocolloid sufficiently fluid to penetrate the backing sheet 10 in spite of its tendency to thicken rapidly when applied. In order to prevent the consistency of the hydrogel from building too fast, i.e., becoming too viscous to properly penetrate the backing sheet 10, a continuous processing mixer 16 (FIG. 1) which includes rotating auger 18 is chilled to help remove heat produced during mixing and keep the hydrogel cool until applied to the backing 10. This can be accomplished by providing the processing mixer 16 with a cooling jacket through which a coolant such as a chilled mixture of water and ethylene glycol is passed during operation. The components of the hydrogel are continuously added to the mixer 16 during operation. While any suitable mixer 16 can be used, one suitable mixer is a five-inch continuous processing mixer manufactured by Teledyne Readco Company of York, Pa. The coolant passed through the processing mixer 16 can be maintained at about 0.degree. C. The temperature of the fluid hydrogel 20 as it flows onto the exposed surface of the backing sheet 10 is important for controlling the infiltration of the coating into the backing sheet 10. The coolant will, under typical operating conditions, keep the extruded hydrogel 20 at a temperature of about 9.degree. C. to 14.degree. C. as it comes into contact with the backing 10. If deeper penetration is desired, the temperature of the hydrogel is lowered to about 9.degree. C. for a typical hydrogel formulation. If less penetration is wanted, the temperature is raised closer to 15.degree. C.

The hydrogel produced by the processing mixer 16, which is in a chilled fluid condition, is expelled at 20 onto the exposed upper surface of the backing sheet 10 adjacent to a knife blade 22 of a knife coater which is held in spaced relationship above a rotatable support roll 23. The distance between the knife 22 and the roll 23 is controlled in any suitable manner, as by means of adjustment screws (not shown) or, if desired, the desired gap or spacing between the knife 22 and roll 23 can be preset to accommodate the backing sheet 10 and the thickness of the hydrogel coating 24 that is being applied to the exposed surface of the backing sheet 10.

In accordance with the invention, the medication-containing hydrogel 20 is applied so as to penetrate a substantial portion of the backing sheet 10, e.g., typically between one-fourth to nine-tenths the thickness of the backing sheet 10. The penetration of the coating 24 into the backing 10 can be seen in FIG. 5. In this case the hydrogel coating 24 has penetrated about three-fourths of the way through the backing sheet 10 to provide an upper, i.e., internal layer 24a of hydrocolloidal material within the pores between the fibers making up the porous backing sheet 10. The hydrogel material thus includes two layers as seen in FIG. 5; the external coating layer 24 with an exposed pressure-sensitive surface 24b and the upper internal portion 24a which infiltrates and becomes solidified within the backing in the interstices between the fibers that make up the porous backing sheet 10.

In one product with very good characteristics the backing sheet 10 is 5.5 mils in thickness and the external part of the coating layer 24 is 8 mils in thickness to provide a combined thickness for the patch when applied to the body of 13.5 mils. The external hydrogel layer 24 is purposely maintained relatively thin. The hydrocolloidal adhesive reservoir infiltrates into the backing to a depth of about 2-5 mils to provide a total hydrocolloid layer, including both the internal and external portions, of about 10-13 mils. Because of its thickness, the medication-containing reservoir provides a very adequate supply of medication to assure sustained release of the medication over an extended period of time, e.g., six to eight hours or more. During use, the medication in the internal reservoir portion 24a stored within the backing sheet 10 migrates from within the backing sheet 10 through the external coating layer 24 and then passes through the skin to provide sustained release of the medication into the body of the patient.

After the hydrogel layer 24 is applied to the backing 10, the backing sheet continues moving toward the right as seen in FIG. 1 into close proximity with an oven or heater, in this case a radiant electric heater 25 which radiates heat onto the hydrogel coating layer 24, raising its temperature to about 140.degree. F. and causing it to cure, i.e., to set up as a solid that is sufficiently stable to maintain its own shape and resist flow during storage or use. Once the heater 25 has warmed the hydrogel coating 24, it will be solidified and dimensionally stable. A liner sheet 26 such as polyethylene coated paper is then applied continuously by pressing it onto the exposed surface of the hydrogel layer 24 as the liner sheet 26 passes beneath a rotating roll 28. The assembled laminate 34 then moves further toward the right in the figure where a die press 30 stamps separate patches 32 from the sheet material.

The hydrogel 20, 24 comprises a hydrocolloidal dispersion of a hydrophilic natural or synthetic gel-forming polymer, a hydrophilic humectant, a biomedically active substance or medication, i.e., a medicament, and a hydrophilic adhesive substance such as an aqueous dispersion of an acrylic adhesive.

The polymer can comprise a natural gum such as gum karaya, gum acacia, locust bean gum, guar gum, or other polysaccharide as well as synthetically formulated polysaccharides, e.g., modified guar gum, maltodextrin, or celluloses such as carboxymethyl cellulose and carboxypropyl cellulose. The polymer can also comprise a synthetic polymer such as polyacrylamide and its cogeners or polyacrylic acid. Polyacrylamide is sold under the trademark Polytec.RTM. 31x a polyacrylamide by Tecna Corp., Belleville, N.J.

The humectant can comprise a polyhydric alcohol such as glycerol, propylene glycol, ethylene glycol, or sorbitol.

The adhesive can comprise any suitable biocompatible hydrophilic adhesive such as a resin emulsion adhesive, e.g., an acrylate emulsion adhesive or a copolymer of vinyl acetate and dioctyl maleate. The most outstanding results have been achieved with an acrylic emulsion adhesive. Other hydrophilic adhesives that can be used include an acrylic ester copolymer and a vinyl acetate resin.

Any of a variety of topical medications can be used in accordance with the present invention. When the patch is used as an analgesic, these include trolamine salicylate, methyl salicylate, menthol, camphor, eucalyptus oil, spearmint oil, or a combination thereof. In other applications, the medication can include anti-pruritic agents or anti-inflammatory agent such as hydrocortisone, or anesthetic agents such as benzocaine or lidocaine. Also included are non-steroidal anti-inflammatory agents such as ibuprofen, especially the S-isomer of ibuprofen. Other medications include keratolytic agents such as salicylic acid, and rubefacient agents such as capsicum.

In FIG. 2 the finished patch 32 is seen applied to the surface of the body with the backing 10 exposed and the pressure-sensitive hydrogel layer 24 bonded to the skin.

In FIG. 3 is shown a package containing the finished patch 32 as it appears during shipment and storage. The package 36 comprises a pouch including lower and upper layers of paper 35, 37 or other suitable packaging material such as metal foil coated paper which is sealed to itself along its edges, e.g., at 36a, 36b to provide a sealed pouch containing the finished patch 32.

As shown in FIGS. 4 and 5, the finished patch 32 includes the porous backing 10, the hydrogel coating including the lower, i.e., external hydrogel coating layer 24 and the upper or internal portion 24a that permeates the backing 10. The upper surface 26a of the liner sheet 26 is a release surface for facilitating its removal. Before use, the liner sheet 26 is removed by pulling it off the patch as shown at the right in FIG. 4 to expose the pressure-sensitive surface of the layer 24 which is then applied to the skin as shown in FIG. 2.

During use, the upper or internal reservoir portion 24a that infiltrates the backing 10 and is solidified therein serves to store the medication within the backing 10 so that the medication migrates over time from its location at 24a within the backing 10 through the external coating layer 24 and then passes through the skin to provide sustained release of the medication into the body of the patient.

The porosity of the backing 10 combined with the water compatibility of the hydrocolloidal dispersion also makes the patch non-occlusive so that moisture from the body can evaporate through the patch into the atmosphere. The moisture vapor transmission rate (MVTR) of the skin alone under various conditions is typically from about 70 to about 149 g/m.sup.2 /24 hr while the medication applying patch of the present invention is about 612 to 1952 g/m.sup.2 /24 hr. This shows that the invention is non-occlusive because in a given period of time about 8 to 14 times more moisture vapor is transmitted through the patch of the present invention than through the skin. Prior medication-applying patches that employed a rubber backing allow virtually no moisture evaporation from the skin. By contrast, the non-occlusive patch of the present invention will not interfere with moisture evaporation from the skin. This is important because the evaporation of moisture from the skin helps the skin to act in its normal capacity as a barrier to externally applied compounds which, if absorbed in excessive amounts, can produce toxic reactions or skin irritation. The invention thus enables the barrier function of the stratum corneum to be maintained.

When used as an analgesic patch, the present invention provides outstanding results in relieving pain such as arthritis pain and backache pain, as well as muscular aches and strains. Because of the thinness of the patch, it is perceived as being more comfortable, more flexible, less obtrusive and is more acceptable to the patient. The backing 10 is rendered so translucent by infiltration of the hydrocolloidal gel that the patch is very inconspicuous on the skin. The entire thickness of the analgesic patch is about 13.5 mils.

The invention will be better understood by reference to the following examples:

Many variations of the present invention within the scope of the appended claims will be apparent to those skilled in the art once the principles described herein are understood.