Transdermal Therapeutic Systems for the Administration of Naloxone, Naltrexone and Nalbuphine

This invention relates to transdermal therapeutic system for the parenteral administration of naloxone, naltrexone and nalbuphine through intact skin.

This application is related to the copending coassigned patent application Ser. No. 06/659,121 of like date herewith of Taskovich et al. for Skin Permeation Enhancer Compositions.

Naloxone, naltrexone and nalbuphine are known, chemically similar drugs and are described in the 1984 USAN and the USP Dictionary of Drug Names, United States Pharmacopiea Convention, Inc., Rockville, MD pp. 327 and 378 (1983). The therapeutic administration of naloxone and nalbuphine is currently limited to injection or infusion typically from solution of the hydrochloride and naltrexone is under investigation for similar administration. Although various types of transdermal therapeutic systems for delivering a wide variety of drugs are known to the art, such as described in U.S. Pat. Nos. 3,598,122, 3,598,123, 4,379,454, 4,286,592, and 4,317,557, (which are all incorporated herein by reference) for example, none of these patents are directed specifically to systems for the transdermal delivery of either naloxone, naltrexone or nalbuphine. We found that the permeability through skin of these drugs is too low to produce any therapeutic effect from a reasonably sized therapeutic system. When we attempted to increase their permeation through skin by the contemporaneous administration of conventional permeation enhancers we were either unsuccessful in increasing the flux or we observed unacceptable levels of irritation to the skin.

According to this invention we have discovered that the base form of naloxone, naltrexone and nalbuphine can be delivered through intact skin at fluxes capable of producing therapeutic effects if delivered in the presence of permeation enhancing amounts of polyethylene glycol monolaurate (PEGML) and have provided drug/permeation enhancer reservoir compositions and transdermal therapeutic systems incorporating the same which are useful in the transdermal delivery of naloxone, naltrexone and nalbuphine.

It is accordingly an object of this invention to provide transdermal therapeutic systems for the delivery of naloxone, naltrexone and nalbuphine through intact skin.

It is another object of this invention to provide drug reservoir/permeation enhancer compositions for use in the transdermal delivery of naloxone, naltrexone and nalbuphine.

It is another object of this invention to provide a method for the transdermal administration of naloxone, naltrexone and nalbuphine.

These and other objects and advantages will be readily apparent from the following description with reference to the accompanying drawings wherein:

FIG. 1 is a cross-sectional, perspective view through one embodiment of transdermal therapeutic system according to this invention.

FIG. 2 is a cross-sectional view through another embodiment of transdermal therapeutic system according to this invention.

According to our invention we have discovered that therapeutic amounts of naloxone, naltrexone or nalbuphine can be delivered transdermally by topical application of the drug in the base form to the skin in the presence of flux enhancing amounts of polyethylene glycol monolaurate (PEGML). In addition, by appropriate selection of the thermodynamic activity of the drug and the PEGML in the reservoir compositions, the drug can be delivered over extended periods of time without producing unacceptable irritation to the skin. Although the drugs are currently administered by injection in the form of the water soluble hydrochloride, our transdermal systems utilize the drugs in the form of the base, and as used herein the term, "drug" refers to the base form of naloxone, naltrexone and nalbuphine.

Referring now to FIG. 1, a transdermal therapeutic system 1 according to this invention is shown which comprises a drug/permeation enhancer reservoir 2 in the form of matrix having drug and PEGML dispersed therethrough. The reservoir 2 is covered by an impermeable backing 3 which is preferably sized slightly larger in circumference than reservoir 2. Means 4 for maintaining the system on the skin may either be fabricated together with or provided separately from the remaining elements of the system which means in the embodiment of FIG. 1 takes the form of an adhesive overlay. The use of an adhesive overlay with this invention is preferred to the use of an inline adhesive applied to the skin proximal surface of reservoir 2 because PEGML adversely affects the adhesive properties of most pharmaceutically acceptable contact adhesives. For this reason, impermeable backing layer 3 is preferably sized slightly larger than the reservoir 2 to provide a peripheral area around reservoir 2 free of PEGML to prevent adverse interaction between the adhesive in the overlay 4 and any of the PEGML which may seep from under the base of reservoir 2 in use. A strippable release liner 5, adapted to be removed prior to application would normally be included in the packaged product.

Various materials suited for the fabrication of the various layers are disclosed in the aforementioned patents. Due to the solubility characteristics of the drug and PEGML, the matrix is preferably an anhydrous matrix, such as natural or synthetic rubbers, or other polymeric material, thickened mineral oil or petroleum jelly, for example. The preferred embodiment according to this invention is fabricated from an ethylene vinylacetate (EVA) co-polymer of the type described in U.S. Pat. No. 4,144,317, preferably those having a vinylacetate (VA) content in the range of about 28 to 60% VA. The drug is preferably dispersed through the matrix at a concentration in excess of saturation, the amount of the excess being a function of the intended useful life of the system. The PEGML is initially dispersed through the reservoir, preferably at a concentration below unit activity, i.e., below saturation concentrations in the reservoir, and preferably within the range of activity 0.25 to 0.60. Various grades of PEGML are commercially available differing in average molecular weight of the polyethylene glycol (PEG) component. The lower the molecular weight of the PEG component, the greater is the drug flux obtainable. Thus we prefer PEG (200-400) ML for use in our invention.

In addition to the drug and PEGML which are essential to the invention, the matrix may also contain other materials such as dyes, pigments, inert fillers or other conventional components of transdermal therapeutic systems known to the art. In particular, an inert, non-absorbent filler such as titanium dioxide for example, can be added to the matrix in order to reduce the amount of naloxone contained in the unused and in the depleted systems.

Typical reservoir formulations are described in Table 1.

Since the drugs are substantially insoluble in EVA, the total loading of in the matrix can be determined based on desired hourly release rates and duration of administration. When the reservoir compositions are fabricated with the initial PEGML activity of approximately 0.50, relatively constant transdermal fluxes within the range of from about 20 to 40 .mu.g/cm.sup.2 /hr are obtainable. Such fluxes appear to be maintained so long as drug is present at unit activity and the activity of the PEGML remains above about 0.20.

Referring now to FIG. 2 another embodiment of this invention is shown in place upon the skin 17 of a patient. In this embodiment the transdermal therapeutic system 10 comprises a multilaminate drug/enhancer reservoir 11 having at least two zones 12 and 14. Zone 12 consists of drug/PEGML reservoir substantially as described with respect to FIG. 1. Zone 14 comprises a PEGML reservoir which is preferably made from substantially the same matrix material as used to form zone 12 and which is substantially free of any undissolved drug. A rate-controlling membrane 13 for controlling the release rate of PEGML from zone 14 into zone 12 and from zone 12 to the skin may also be utilized between zones 12 and 14 if desired. Suitable rate-controlling membranes may be formed from materials having a lower permeability to PEGML than the material used to form reservoir zone 14. If an EVA membrane is used in conjunction with EVA matrix the membrane would preferably have a lower VA content than the matrix.

An advantage of the system described in FIG. 2 is that the drug loaded zone 12 is concentrated at the skin surface rather than throughout the entire mass of the reservoir and can function to reduce the amount of drug present in the system while providing an adequate PEGML reservoir for delivery throughout the anticipated system lifetime. The PEGML is preferably incorporated in the reservoir 11 such that its concentration in zone 12 is initially below unit activity and is present in sufficient amounts to maintain the activity within the activity levels described above over the anticipated life of the system. It should be understood that after fabrication of the system the PEGML wll equilibriate throughout reservoir 11. Thus, the equilibrium concentration at the skin surface, is not dependent upon the initial concentration of PEGML in the zone 14 or 12 but on the final equilibrium concentration. Superimposed over the drug enhancer reservoir 11 is an impermeable backing 15 and adhesive overlay 16 as described above with respect to FIG. 1. In addition, a strippable release liner would preferably be provided on the system prior to use as described with respect to FIG. 1 and removed prior to application to the skin 17.

A transdermal therapeutic system according to FIG. 1 was fabricated from 35 wt % naloxone base, 25 wt % PEG 200 ML and 40 wt % EVA (40% VA) by dissolving all components in methyl chloride. The solution was cast onto a glass substrate and dried to remove all solvent. The resulting reservoir composition was removed from the glass substrate and pressed between two siliconized release liners to a thickness of 12 mils and the appropriate sized reservoir cut from the sandwich structure so formed. The appropriately sized plug of reservoir composition so produced was applied to an impermeable, EVA coated, aluminized polyester backing having exterior dimensions slightly larger than that of the reservoir to leave a slight flange about the periphery of the reservoir. The thus formed laminate was then applied on intact human skin by means of an adhesive overlay comprising a microfoam adhesive pad. Systems as described above having a surface area of 1 cm.sup.2 were applied to human forearms for a period of 24 hours. They were removed and fresh systems were applied to half of the test sites for another 24 hours. The apparent drug flux through the skin determined from residual drug in the depleted systems was 30.58.+-.8.5 .mu.g/cm.sup.2 /hr for Day 1 and 30.77.+-.11.72 .mu.g/cm.sup.2 /hr for Day 2. No observable irritation or erythema was noted 24 hours after removal of the systems.

The therapeutic transdermal delivery rate for naloxone appears to be in the range from about 9 to 30 mg/day with an average of about 15 mg. Thus, systems fabricated as described above having skin contacting surfaces from about 10 to 60 cm.sup.2 should be capable of delivering naloxone to patients within the therapeutic dosage range for periods of time as long as 48 hours although larger and smaller systems are also contemplated hereunder.

The in vitro flux of naloxone and nalbuphine base through cadaver skin into an infinite sink at 37.degree. C. from EVA matrices with and without PEGML were measured as follows:

Accordingly, substitution of nalbuphine base for the naloxone base in systems of Example I should result in nalbuphine delivery at comparable rates. The hourly dosage rates of naloxone and nalbuphine are similar, so similarly sized systems should be suitable for transdermal nalbuphine therapy.

The in vitro skin flux of naloxone and naltrexone base through cadaver skin into an infinite sink at 32.degree. C. from mineral oil donors containing the drug without PEGML and from samples saturated with PEGML were measured as follows:

Accordingly substitution of naltrexone base for the naloxone base in the systems of Example I should result in naltrexone delivery at comparable rates. The hourly dosage rates of naloxone and naltrexone are similar so similar sized systems should be suitable for transdermal naltrexone therapy.

Having thus generally described our invention and having provided a specific examples thereof, it will be apparent that various modifications can be made by workers skilled in the art without departing from the scope of the invention which is limited only by the following claims.