TRANSDERMAL SYSTEM II

Abstract: A transdermal therapeutic system is provided which is adapted for delivery of a biologically active agent over an ex­ tended time period said system comprising a matrix containing an agent disposed therein, the intended body distal surface of said matric having fibrous reinforcing means embedded therein, said matrix being capable of firm adhesion to the skin but with a peel strength sufficiently low for removal without dis­ comfort. The reinforcing means comprises a stretchable fabric formed of either randomly or orientated bonded fibres to form an isotrophic web substantially equally deformable in all direc­ tions, or anisotrophic web formed of a multiplicity of continu­ ous generally parallel fibres having randomly orientated sec­ ond fibres bonded transversly thereto so as to be deformable primarily in a direction perpendicular to the continuous fibres.

Description: This invention relates to the parenteral delivery of biologically active materials and more particularly to the delivery of such materials to the human body in therapeutic amounts through sensitive areas of intact skin. Certain drugs and other agents are known to be capable of being topically administered to the skin to produce a local or systemic effect upon absorption into the skin. (As used herein, the term "agent" is employed in its broadest sense and applies to any drug or other substance which is delivered to the body to produce a desired, usually beneficial, effect on the recipient.) Originally this was accomplished by application of creams, ointments, gels, solutions or suspensions of the agent in a suitable carrier. This mode of application did not permit precise control of the dose or rate of administration because the amount of agent applied and the surface area covered were highly variable. Accordingly, transdermal delivery devices which deliver known amounts of drug to controlled areas of skin were developed. Representative devices are shown in U.S. Patents are 3249109, 3598122, 4144317, 4201211, 4262003, 4307717, and 4379454, for example, which patents are incorporated herein by reference. The simplest type of a transdermal delivery device is an agent reservoir of predetermined size and composition, usually a matrix material containing dissolved or dispersed agent, maintained on a predetermined area of the skin for a predetermined period of time by adhesive or other means. Such matrix systems have the advantage of being easily fabricated and are generally of lower cost than more sophisiticated rate controlled systems, although the rate of release of an agent from a simple matrix tends to decrease as a function of the time of use. The site of administration of transdermal delivery devices have been selected at various locations such as behind the ear, on the chest or on the thigh for various reasons such as desired skin permeability to an agent, convenience or cosmetic reasons. It has been known for some time that permeability of human skin varies from site to site and that for certain agents scrotal skin tends to have a higher permability than other skin. Prior to our invention however the only means by which agents were administered through intact scrotal skin was by application of an ointment, cream, gel or solution of the agent and we were unaware of any delivery device suitable for transcrotal drug delivery. This was because the shape, texture, environment and sensitivity of the scrotum presented a combination of conditions which were incompatible with the application of prior art delivery devices and the maintenance of such a device in place for an extended time period without discomfort or other adverse side effects. For example, we have found that the shape and texture of scrotal skin requires a highly flexible device possessing a certain amount of compliance or non-elastic stretch in order to be capable of comfortably conforming to the wrinkles, folds and irregular shape of scrotal skin in agent transmitting relationship thereto and thereafter remain in this slightly deformed condition rather than returning to its original configuration. Patient discomfort is a crucial factor in patient compliance and we have found that comfort depends not only on flexibility and stretchability but also on the texture of the device and the sensations attendant to removal. Typical contact adhesives, belts, buckles and elastic bands were all found to be unacceptably uncomfortable. According to our invention we have devised a transdermal delivery device which is particularly adapted for the topical and systemic administration of agents to the skin at sensitive body sites such as the scrotum, labia, penis or underside of the breast, for example, for which heretofore there have been no suitable agent delivery platforms. Typical agents, by way of non-limiting examples, include androgens such as testosterone, estrogens such as estradiol, progestins such a progesterone, steroids such as hydrocortisone and cyproterone, peptides such as LHRH and interferon, and antiviral agents such as acyclovir and phenolphthalein. As used herein, the identification of an agent to be delivered includes not only the compound per se but also its topically administrable prodrugs, active metabolites and prodrugs of the active metabolites. Thus for example the reference to testosterone includes testosterone per se, its prodrugs such as testosterone enanthate, its active metabolite, dihydrotestosterone and its prodrug dihydrotestosterone enanthate, for example. High tack transdermal therapeutic systems for the delivery of biologically active agents are known from JP-A-60-75428 to include a stretchable fabric with orientated bonds. However the tack is achieved by means of a separate adhesive layer. In our GB-A-2161073 we have described a transdermal therapeutic system adapted for the delivery of a biologically active agent for an extended time period comprising:- a matrix containing said agent distributed therein, the intended body distal surface of said matrix having a fibrous reinforcing means embedded therein, The present invention provides a system that is adapted for delivery to a sensitive body location, wherein the reinforcing means comprises a stretchable fabric formed of either randomly orientated bonded fibres to form an isotrophic web substantially equally deformable in all directions, or an anisotrophic web formed of a mutiplicity of continuous, generally parallel fibres having randomly orientated second fibres bonded transversely thereto so as to be deformable primarily in a direction perpendicular to the continuous fibres, and wherein the skin contacting surface of said reservoir has a tack in the range 100 - 300g/cm² at 35°C, such that the system may be readily removed from the sensitive body location without producing discomfort. These and other objects of the invention will be readily apparent from the following description with reference to the accompanying drawings wherein which are included by way of illustration only. Figure 1 represents a cross-section through a perspective view of one embodiment of this invention. Figure 2 is a plot of in vivo testosterone blood levels obtained from embodiments of the invention applied to the scrotum , An agent delivery device 1 according to this invention is shown in FIG. 1. Such a device 1 comprises a reservoir 2 in the form of a non-aqueous polymeric carrier having the agent to be delivered dissolved or dispersed therein, which carrier has a viscosity and strength sufficient to enable the device to maintain its structural integrity during use without oozing, flowing or otherwise disintegrating. In addition, the reservoir has a limited amount of tack to permit it to cling to the skin to which it is applied without actually being adhesively bonded thereto. The carrier may optionally contain skin permeation enhancers, stabilizing agents, or other additives as is known to the art. In order to strengthen the reservoir 2, facilitate handling, application and removal of the device and to provide a textured feel to the body distal portion of the device 1, the body distal surface is provided with reinforcing means 3, typically in the form of a non-woven, woven or knit, relatively open mesh fabric, chemically inert with respect to other components of the system. An impermeable release liner 5, adapted to the easily removed from the body contacting surface of the drug reservoir 2 prior to use would normally be provided to protect the system in its package. Reinforcing means 3 is bonded to the device, embedded either in the upper surface of reservoir 2 or, in a preferred embodiment, in a discrete layer of bonding agent 4 having characteristics different from those of the carrier forming reservoir 2. The device of this invention must be sufficiently flexible and compliant to closely conform to the scrotal or other skin and to be maintained in agent transmitting contact without adhesive bonding. This is accomplished by a combination of flexibility, compliance and the non-adhesive tack of the reservoir as hereafter described in detail. Suitable carriers for the fabrication of the reservoir can be selected from a wide variety of materials known to the art, provided they possess the required compatibility with the agent, structural strength, flexibility and tackiness required. As noted in the Patents cited above, such materials include, without limitation, tacky natural and synthetic polymers and blends such as natural or synthetic rubbers, and ethylene vinylacetate (EVA) copolymers such as are disclosed for example in U.S. Patents 4069307 and 4144317 which as incorporated herein by reference. EVA polymers having a VA content of from about 28-61% and preferably about 40-60% possess characteristics of solubility, permeability and tack to be suitable for the delivery of a wide variety of agents according to this invention. Although any agent which is suitable for transdermal administration can be delivered according to this invention certain agents are particularly suited for administration from devices according to this invention. Testosterone constitutes a preferred agent according to this invention, particularly for use in treatment of hypogonadal males. Embodiments of our invention are capable of producing testosterone blood levels which exhibit a pattern more closely approximating the normal circadian hormone pattern via transcrotal administration than are obtained by application to sites other than the scrotum. Other preferred agents include estradiol, which can be administered to the labia for treatment of post menopausal disorder for example and progesterone which can be administered to the breast to correct oestrogen-progesterone imbalance in women with benign breast diseases as suggested by J. De Boever et al., Variation of Progesterone, 20 α-Dihydroprogesterone and Oestradiol Concentration in Human Mammary Tissue and Blood After Topical Administration of Progesterone , Percutaneous Absorption of Steroids, Academic Press, New York, pp. 259-265 (1980) and R. Sitruk-Ware et al., Treatment of Benign Breast Diseases by Progesterone Applied Topically , Ibid. pp. 219-229. Anti-viral agents, particularly for treating herpes, such as interferon, acyclovir or phenolphthalein as disclosed in U.S. Patent 4256763 which is incorporated herein by reference may also be administered according to this invention. Antiandrogens which have known utility in treatment of prostatic cancer as well as application as contraceptives are also particularly suitable. Cyproterone acetate either alone or with LHRH can be administered according to this invention and thereby avoid the 90-95% first-pass metabolism encountered through oral administration. The initial loading of agent in the carrier will determine the useful life of the device, useful lives of from about 8 hours to 1 week being typical for transdermal devices generally. This invention can be used for such time periods, however, certain preferred embodiments are particularly adapted for administration periods of up to about 24 hours. The concentration of the agent in the carrier can vary over relatively wide limits, the maximum concentration being determined by the amount of agent that can be received in the carrier without producing adverse histological effects such as irritation, an unacceptably high initial pulse of agent into the body or adverse effects on the characteristics of the device such as loss of tackiness, viscosity or deterioration of other properties. If the device contains agent in an amount in excess of saturation, the excess will function as a unit activity source until depleted. If subsaturated systems are employed, the release rate will tend to decrease more rapidly with time of use than with saturated systems. This characteristic is particularly useful with hormones such as testosterone in which a circadian variation in blood level is normal. With respect to certain specific embodiments, we have found it desirable to maintain the agent concentration below that level at which the agent crystalizes to prevent loss of tackiness. Suitable reinforcing means 3 include spun bonded polyester and polyamide fabrics such as noted above as well as natural or synthetic woven or knit fabrics, and chopped rovings which may, in certain embodiments, be made from, or be coated with a material having the solubility characteristics for a particular agent and matrix with respect to which it is incorporated The reinforcing means are preferably incorporated as stretchable, typically spun-bonded, fabrics consisting of either randomly oriented bonded fibers which form an isotropic web equally deformable in all directions or an anisotropic web formed from a multiplicity of continuous generally parallel fibers having randomly oriented fibers bonded transversely thereto which is deformable primarily in the direction perpendicular to the continuous fibers. Woven and knit fabrics can also be used. These fabrics tend to curl when the release liner is removed and are preferably applied in a manner in which the curl tends to envelop the scrotum rather then separate therefrom to assist in maintaining contact. The reinforcing means 3 can be embedded in the upper surface of the reservoir 2 or may be embedded in the upper surface of a layer of bonding agent 4 which is applied over reservoir 2. The reinforcing means is preferably not totally submerged in the material in which it is embedded so that the skin distal surface of the device retains a textured feel rather than presenting a smooth surface. By embedding the reinforcement means 3 in a bonding agent formed of a material different from the carrier, it is possible to use a bonding material which is substantially impermeable to the drug to be delivered and thereby reduce the amount of agent that can be released through the skin distal surface. The bonding agent should be selected to be adherent to both the matrix material and the reinforcing means and be relatively impermeable to the agent to be delivered. Polyisobutylene (PIB) and silicone adhesives, for example, are useful for many combinations of materials. In transcrotal delivery of testosterone, for example, release of testosterone to a female sexual partner is undesirable. This embodiment of our invention provides an integral impermeable barrier without impairing the textured feel or other characteristics of the skin distal surface of the device. Delivery devices according to this invention normally comprise devices having a surface area in the range of from about 15-75 cm², depending on site of application. Smaller systems have a tendency to fall off prematurely and larger systems may be too large for the average penis, scrotum, labia or breast. The preferred range is about 20-60 cm², a typical transcrotal device being fabricated as an approximately 40cm² generally rectangular patch with rounded corners. The patches are intended to be applied and left in place preferably while wearing close fitting clothing such as jock strap or jockey shorts, panties or brassiere for example to protect the device from unnecessary physical contact or motion and assist in maintaining the device in contact with the skin, for the desired time period. When applied to the penis or breast, the devices would be configured appropriately for their environment of use as elongated strips or kidney shaped devices respectively. The sensitivity of scrotal, penile, labial, and mammary skin and their sometimes irregular and changing configurations imposes significant constraints on the characteristics of a delivery device according to this invention. For example, the device must be both sufficiently thin, flexible and stretchable so as to easily conform to the configuration of the site of application and have sufficient non-adhesive tack to stay in skin contact in a manner which does not create discomfort on removal. The required combination of characteristics can be obtained from devices having a thickness in a range from approximately 2 to 10 mil with approximately 3 to 5 mil being preferred. The non-adhesive tack of the skin contacting surface should be sufficiently high to maintain contact during use and sufficiently low to be removable without pain, discomfort or irritation. Peel strengths from skin in the range of 1-20 gm/cm were contemplated but this value is extremely difficult to measure accurately or reproducibly. Accordingly, the properties possessed by the devices of this invention have been quantified by test procedures which are accurate and reproducible in vitro . A Polykon Digital Probe Tack Tester, Model #80-20-01 was used to quantify the tack possessed by devices according to this invention. In the test procedure the probe of the Tack Tester is forced into the surface to be tested at 35°C with a contact pressure of 500 g/cm² for 10 seconds and thereafter withdrawn from the surface at a rate of 1 cm/sec. The maximum force exerted before the probe releases from the surface is recorded. The optimum maximum and minimum tack values for devices according to this invention are in the range of about 100-300 g/cm². Tack values referred to hereinafter are determined by this test. In addition to the tack of the body contacting surface, the device of this invention also possesses certain required characteristics of modulus, stress decay and elongation in at least one dimension when measured at room temperature (approximately 20°C). When anisotropic reinforcing means are employed, the following characteristics apply to deformation along the weakest axis. The device should have an extension modulus at 15% extension in the range of 1000-15,000 g/cm² and preferably 1000-5000 g/cm². It should also possess a stress decay in the range of about 25% to 45% within 5 minutes after a 15% extension. In addition a 2 cm wide strip of this device should require an elongation force of from about 30-300 gm and preferably 50-150 gm to produce a 15% extension of the device. The above characteristics of the device can be obtained by appropriate combination of the materials forming the reinforcing means and the reservoir if these materials have certain characteristics. The reinforcing means should have a modulus at 15% extension of from about 800 to 60,000 g/cm² and preferably 1500-15,000 gm/cm² with stress decay from about 30-45% in 5 minutes after a 15% elongation. In the event a bonding layer is incorporated, the bonding layer is preferably selected from a material that, at the thickness used, does not cause the modulus or stress relaxation of the reinforcing means/bonding agent composite to vary by more than about 5% from that of the reinforcing means alone. The reservoir should have an extension modulus significantly lower than that of the reinforcing means, typically less than 1500 g/cm² and preferably in the range of about 800-1200 g/cm²; a stress decay of less than 25% and preferably from about 10-20% in 5 minutes at 15% extension. Having thus generally described our invention, the following examples are provided. EXAMPLE 1 A spun-bonded polyester fabric, 0.3 oz/yd² (equivalent to 1 mg/cm²) sold by Chicopee Mills as Fabric Code No. 9123, was laid upon a release surface of an impermeable silicone-coated polyester film and a 50/50 mixture of low average molecular weight (35,000) and high average molecular weight (1,200,000) polyisobutylene (PIB) in heptane was cast onto the fabric at a loading of 1 mg PIB/cm². Upon evaporation of the heptane, the upper surface of the fabric was sufficiently exposed to have a distinct textured feel with the PIB concentrated in the lower portion of the fabric at a thickness of about 0.4 mils. A mixture of 2 wt% testosterone and 98 wt% EVA (40% VA) was dissolved in methylene chloride and cast onto a fluorocarbon coated polyester release liner available from 3M Co. to produce, after evaporation of the solvent, a reservoir loading of 12.5 mg/cm² containing 0.25 mg testosterone per cm². The spun bonded polyester/PIB laminate was removed from its release liner and the PIB surface was laminated and bonded to the testosterone reservoir at 90°C. When the resultant product is die cut into 20 cm², 40 cm² and 60 cm² rectangles with rounded corners it provides systems having testosterone loadings of 5, 10 and 15 mg respectively. These devices are suitable for the transcrotal administration of testosterone. The tack of the systems was about 100g/cm², the elongation modulus was 1670 g/cm², the stress decay was 33% and the elongation force was 55 gm. EXAMPLES 2-11 Systems for topical application of interferon, acyclovir, cytopreterone acetate, LHRH and phenolphthalein can be fabricated according to the general procedures of Example 1 from the formulations in Table 2. Example # Drug Drug Loading gm/cm² Reinforcing Means Matrix Bonding Agent 2. Interferon 0.20 spun bonded polyester hydrophyllic silicone copolymer (Dow Chemical None 3. Acyclovir 0.25 spun bonded polyester EVA (40% VA) PIB 4. Cyproterone Acetate 0.30 spun bonded polyester EVA (51% VA) None 5. LHRH 0.10 spun bonded polyester EVA (40% VA) Silicone Adhesive Dow-355 6. Phenolphthalein 0.30 spun bonded nylon EVA (51% VA) None EXAMPLE 7 When testosterone ointments were used according to the prior art, it had been reported that female sexual partners were experiencing adverse reactions such as increased hair growth as a result of the transfer of testosterone during intercourse. An experiment was performed to compare how much testosterone was transferred from the back side of devices fabricate according to Example 1 with the amount transferred using Percutacrine ointment. 20 cm² patches produced according to Example 1 were applied to the scrotums of four subjects and left in place for three hours. The patches were removed and the back (skin distal) surface of the patch was rubbed vigorously on the forearm of each subject. The residual testosterone on each scrotum and forearm was recovered by wiping three times with a cotton swab soaked in isopropyl alcohol and thereafter assayed. 0.2 cc Percutacrine ointment gas applied to a 20 cm² gauze pad and applied to the thigh of the same four subjects. After three hours the gauze was removed and the subjects forearm was vigorously rubbed over the site of application. The residual testosterone was recovered from the forearm and thigh of each subject and asayed as described above. The results are shown in Table 3. The results indicate that the device of Example 1 provides a barrier to the transport of testosterone from the back surface thereof. The results also indicate that less residual testosterone remains on scrotal skin than on thigh skin.

Claims: A trans-dermal therapeutic system (1) adapted for the delivery of a biologically active agent for an extended time period comprising:- a matrix (2) containing said agent distributed therein, the intended body distal surface of said matrix having a fibrous reinforcing means (3) embedded therein, characterised in that the system is adapted for delivery to a sensitive body location, in that the reinforcing means comprises a stretchable fabric formed of either randomly orientated bonded fibres to form an isotrophic web substantially equally deformable in all directions, or an anisotrophic web formed of a mutiplicity of continuous, generally parallel fibres having randomly orientated second fibres bonded transversely thereto so as to be deformable primarily in a direction perpendicular to the continuous fibres, and in that the skin contacting surface of said reservoir has a tack in the range 100 - 300g/cm² at 35°C such that the system may be readily removed from the sensitive body location without producing discomfort. A system according to claim 1 characterised in that when the reinforcing means is anisotrophic, the system is formed with an extension modulus at about 15% extension in the range of 1000 - 1500 g/cm², and a stress decay from 15% elongation in the range of about 25 to 45% within five minutes of said extension. A system according to claim 2 characterised in that a 2 cm. wide strip of the device requires an elongation force of 30 - 300 gms. to produce the 15% extension. A system according to claim 1 characterised in that the reinforcing means has a modulus at 15% extension or from 800 to 60,000 g/cm² and a stress decay of 30 to 45% in five minutes after 15% elongation. A system according to any preceding claim characterised by a bonding layer (4), bonding said matrix to said reinforcing means, said bonding layer being formed of a material which is substantially impermeable to the active agent thereby to reduce the amount of agent released through the body distal surface of the system. A system according to claim 5 characterised in that the bonding layer does not cause the modulus or stress relaxation of the reinforcing means/bonding agent composite to vary by more than 5% from that of the reinforcing means alone. A system according to any of claims 2 to 6 characterised in that the reservoir has an extension modulus less than 1500 g/cm² and a stress decay of less than 25% in five minutes at 15% extension. A system according to any preceding claim characterised in that the reservoir is formed of an EVA polymer having a VA content of 28 to 61%. A system according to any preceding claim characterised in that the active agent is selected from testosterone, estadiol, interferon, acyclovir, phenolphthalein, antiantrogens, and cyproterone with or without LHRH. A system according to any preceding claim characterised in that the active agent is testosterone, and in that the system is adapted for application to male genitalia by non-elastic stretch about the genitalia to retain the same in testosterone transmitting relationship. A system according to claim 10 characterised in that the fibrous reinforcing means is embedded in the upper surface of, said reservoir to a depth that does not penetrate through said skin contacting surface and does not totally submerge said reinforcing means in said reservoir, said embedded fibrous reinforcing means forming the body distal surface of said device; said fibrous reinforcing means being non-elastically stretchable in at least one direction; whereby the body distal surface of said device retains a fibrous texture and said device is capable of non-adhesively clinging to the skin at sensitive body locations in agent transmitting relationship thereto. A system according to claim 11 characterised in that said reservoir comprises an ethylene/vinyl acetate copolymer having a vinyl acetate content of about 51%, and in that said reinforcing means comprises a spun bonded fabric having a weight of about 10.17 gms/sq metre (0.3 oz./sq. yd.).

Inventors: CAMPBELL, PATRICIA S., ECKENHOFF, JAMES B., PLACE, VIRGIL A.
Applicants: ALZA CORPORATION
Application year: 1986
Main classification: A61M35
IPC codes: A61K9