certain devices prepared and used according to the present invention contain an opioid antagonist dispersed in microspheres . in certain embodiments , the amount of the opioid antagonist incorporated into the microspheres ranges from about 1 % by weight to about 90 % by weight , or from about 5 % by weight to about 70 % by weight , or from about 30 % to about 50 % by weight of the microsphere ( including active ). in the present invention , the opioid antagonist is incorporated into microspheres for use in opioid transdermal delivery devices in order to make the opioid antagonist non - releasable or substantially non - releasable upon topical application of an intact transdermal delivery device comprising the antagonist microspheres . the microspheres preferably comprise a polymeric substance . suitable polymers that can be used to form opioid - containing antagonist microspheres include soluble , insoluble , biodegradable , and non - biodegradable polymers . the use of pharmaceutically acceptable non - toxic polymers is preferred . physicochemical features of the polymers can be selected to provide further abuse resistance of the present invention . for example , hydrolysis of poly ( orthoester ) is catalyzed by acid . thus , abuse via oral ingestion of the opioid - containing portion of a transdermal delivery device containing microspheres of poly ( orthoester ) comprising opioid antagonist would result in degradation of the polymer and release of the opioid antagonist in the acid milieu of the stomach . degradation of microspheres comprising polysaccharides and proteins is catalyzed by enzymatic cleavage . thus , for example , abuse via oral ingestion of the opioid - containing portion of the transdermal delivery device containing microspheres of dextrans would result in degradation of the polymer and release of the opioid antagonist in the gastrointestinal tract . polymers that may be used for the opioid antagonist - containing microspheres of the present invention can generally be classified into three types , namely natural , semi - synthetic and synthetic , based on their sources . the natural biodegradable polymers may be further classified into proteins and polysaccharides . representative natural derived polymers include proteins , such as zein , modified zein , casein , gelatin , gluten , albumin , fetuin , orosomucoid , glycoproteins , collagen , synthetic polypeptides and elastin . biodegradable synthetic polypeptides include , for example , poly -( n - hydroxyalkyl )- l - asparagine , poly -( n - hydroxyalkyl )- l - glutamine , and copolymers of n - hydroxyalkyl - l - asparagine and n - hydroxyalkyl - l - glutamine with other amino acids , e . g ., l - alanine , l - lysine , l - phenylalanine , l - valine , l - tyrosine , and the like . polysaccharides ( e . g ., cellulose , dextrans , polyhyaluronic acid , lipopolysaccharides ), polymers of acrylic and methacrylic esters , and alginic acid , may also be used . synthetically modified , natural ( i . e ., semi - synthetic ) polymers include alkyl celluloses , hydroxyalkyl celluloses , cellulose ethers , cellulose esters , and nitrocelluloses , among others . semi - synthetic biodegradable polymers are produced by modifying natural polymers to produce polymers having altered physicochemical properties such as thermogelling properties , mechanical strength and degradation rates . examples of semi - synthetic , biodegradable polymers suitable for use in the present invention include modified chitosan complexes , chondroitin sulfate - a chitosan complexes , and water soluble , phosphorylated chitosans ( p - chitosans ), and combinations thereof ; such as , for example , alginate - chitosan . lack of immunogenicity and more reproducible and predictable physicochemical properties make synthetic , biodegradable polymers preferable to the natural polymers for drug delivery uses . these polymers may be non - toxic and biodegradable , and delivery devices have been prepared from these polymers . therefore , synthetic biodegradable polymers may be particularly suitable for the microspheres of the present invention . non - limiting examples of synthetic biodegradable polymers include : polyesters , polyethers , poly ( orthoesters ), poly ( vinyl alcohols ), polyamides , polycarbonates , polyacrylamides , polyalkylene glycols , polyalkylene oxides , polyalkylene terephthalates , polyvinyl ethers , polyvinyl esters , polyvinyl halides , polyvinylpyrrolidone , polyglycolides , polysiloxanes , polylactides , polyurethanes and copolymers thereof . non - limiting examples of polyesters include polylactic acid , polyglycolic acid , poly ( lactide - co - glycolide ), poly ( e - caprolactone ), polydioxanone , poly ( ethylene terephthalate ), poly ( malic acid ), poly ( tartronic acid ), polyphosphazenes , poly ( orthoester ), poly ( valeric acid ), poly ( buteric acid ), polyhydroxybutyrate , polyhydroxyvalerate , polyanhydride , and copolymers of the monomers used to synthesize any of the above - mentioned polymers , e . g ., poly ( lactic - co - glycolic acid ) or the copolymer of polyhydroxy butyrate with hydroxyvaleric acid ( biopol ® by zeneca ). copolymers of lactic and glycolic acids , e . g ., poly ( lactic - co - glycolic acid ) ( plga ), have been extensively studied for their use in drug delivery devices such as microspheres . in certain embodiments , the polymer ( e . g ., plga ) can have a molecular weight from about 1 kd to about 100 kd or greater , from about 5 kd to about 60 kd or from about 10 kd to about 40 kd . in certain embodiments , a portion of the plga ( e . g ., from 10 % to about 90 %) can have a molecular weight of less than 20 kd , or less than 15 kd and the corresponding , remaining portion ( e . g ., from 90 % to 10 %) can have a molecular weight of greater than 25 kd , or greater than 35 kd . poly ( e - caprolactone ) may be used in preparing microspheres for use in the present invention . the degradation rate of poly ( e - caprolactone ) is much slower than that of either polyglycolic acid or poly ( lactic - co - glycolic acid ). poly ( e - caprolactone ) has exceptional ability to form blends with many other polymers . copolymers of poly ( e - caprolactone ) can be used to control permeability and mechanical properties of drug delivery devices . polyethers and poly ( orthoesters ) may also be used in preparing microspheres for use in the present invention . these polymers have been incorporated into multiblocks for block polymers having diverse degradation rates , mechanical strength , porosity , diffusivity , and inherent viscosity . examples of polyethers include polyethylene glycol and polypropylene glycol . an example of a multiblock copolymer is poly ( ether ester amide ). additionally , triblock copolymers of poly ( orthoesters ) with various poly ( ethylene glycol ) contents are useful for their stability in water / oil ( w / o ) emulsions , and possess greater efficacy than poly ( orthoester ) when used in preparing microspheres . other useful block copolymers include diblock copolymers of poly ( lactic - co - glycolic acid ) and poly ( ethylene glycol ) ( peg ), triblock copolymers of peg - plga - peg , copolymers of plga and polylysine , and poly ( ester ether ) block copolymers . in certain embodiments , microspheres useful in practicing the present invention are spherically shaped and from about 1 to about 500 microns , from about 1 to about 300 microns , from about 1 to about 200 microns , from about 1 to about 100 microns , from about 300 to about 500 microns , from about 200 to about 500 microns , from about 100 to about 500 microns , from about 125 to about 200 microns , or from about 50 to about 100 microns in diameter . microsphere size may be dependent upon the type of polymer used . in certain embodiments , rather than being spherical , the microspheres may be irregularly shaped , wherein the diameter is considered to be the largest cross - section of the microsphere . in certain embodiments , the microspheres used in the present invention comprise opioid antagonist in an amount of from about 5 % to about 70 % by weight of the microsphere ( including active ). in certain embodiments , the opioid antagonist can be loaded into the microspheres via microencapsulation . techniques for microencapsulation for use in accordance with the present invention are described in u . s . pat . nos . 3 , 161 , 602 ; 3 , 396 , 117 ; 3 , 270 , 100 ; 3 , 405 , 070 ; 3 , 341 , 466 ; 3 , 567 , 650 ; 3 , 875 , 074 ; 4 , 652 , 441 ; 5 , 100 , 669 ; 4 , 438 , 253 ; 4 , 391 , 909 ; 4 , 145 , 184 ; 4 , 277 , 364 ; 5 , 288 , 502 ; and 5 , 665 , 428 . furthermore , the microspheres can be prepared by either solvent evaporation as described , e . g ., by e . mathiowitz , et al ., j . scanning microscopy , 4 , 329 ( 1990 ); l . r . beck , et al ., fertil . steril ., 31 , 545 ( 1979 ); and s . benita , et al , j . pharm . sci . 73 , 1721 ( 1984 ); or by hot - melt microencapsulation , as described , e . g ., by e . mathowitz , et al ., reactive polymers 6 , 275 ( 1987 ); or by spray drying . the microspheres may be prepared by any method known in the art including but not limited to coacervation , phase - separation , solvent evaporation , spray - drying , spray - congealing , pan - coating , fluid bed coating or the like . for purposes of the present invention , a microcapsule can be described functionally as a small container enclosing the contents with a film . the film may be made of synthetic , semi - synthetic , or natural polymer as described above , and can control the release ( or provide no release ) of the contents . the release rate of the contents from a microcapsule is mainly determined by the chemical structure and thickness of the capsule film and size of the microcapsule . in microcapsule formulations , small solid particles of opioid antagonist can be coated with a coating which consists of an organic polymer , hydrocolloid , sugar , wax , fat , metal , or inorganic oxide . in certain embodiments , the opioid antagonist is incorporated into the microspheres using an oil / water ( o / w ) emulsion , a water / oil ( w / o ) emulsion , an oil / oil ( o / o ) emulsion , an oil / water / oil ( o / w / o ) emulsion , an oil / water / water ( o / w / w ) emulsion , water / oil / water ( w / o / w ) emulsion , or a water / oil / oil ( w / o / o ) emulsion , or the like . in certain embodiments , the opioid antagonist is incorporated into the microspheres by microemulsification of a fixed oil and an aqueous solution of a water - soluble opioid antagonist . this emulsion is of the “ water in oil ” type . when the emulsion is of the “ water - in - oil ” type , oil is the continuous phase or external phase and water is the “ dispersed ” or internal phase as opposed to the “ oil in water ” device , where water is the continuous phase . in certain preferred embodiments , the opioid antagonist may be incorporated into the microspheres via a multi - phase emulsification device such as w / o / w . the opioid antagonist may be incorporated into multi - phase microspheres prepared by a multiple emulsion solvent evaporation technique . in this technique , the opioid antagonist is incorporated into biodegradable polymeric microspheres by an emulsification process . the device is suitable for both water soluble and insoluble opioid antagonists . the microspheres of the present invention may be multiphasic polymeric microspheres in which the opioid antagonist is dispersed in oily droplets in a polymeric matrix . the microspheres can be prepared by a multiple emulsion solvent evaporation technique as described in u . s . pat . no . 5 , 288 , 502 . this patent describes a multiple emulsion solvent technique , where the drug is protected within an oily droplet and contact with the polymer , organic solvent , and other potentially denaturing agents is avoided . multiple emulsions are devices in which drops of the oil - dispersed phase themselves contain even smaller aqueous dispersed droplets consisting of a liquid identical with the aqueous continuous phase . they are emulsions of emulsions with high capacity for entrapment of drug , protection of the entrapped drug , ability to introduce incompatible substances into the same device , and prolongation of release . any of a variety of fixed oils may be used in preparing the microspheres , including safflower , soybean , peanut , cotton seed , sesame , or cod liver oil , among others . in certain preferred embodiments , soybean , sesame or safflower oil are used . the oil phase may consist of isohexadecane or liquid paraffin . oil concentration influences the stability of the emulsion . stability is optimal with an oil percentage preferably in a range of 20 - 30 % w / w of the total emulsion . in the multiple emulsion process , the organic phase may be prepared by preparing an emulsion containing the opioid antagonist and a polymeric material . preferably , the opioid antagonist is dispersed in an organic polymer solution in either methylene chloride or ethyl acetate . the resulting primary w / o emulsion is then dispersed into an external aqueous phase to form a second emulsion that comprises microspheres containing the opioid antagonist in the polymeric matrix material ( i . e ., emulsification into the external phase ). the subsequent process steps are similar to the o / w method . the step of dissolving the drug into the internal aqueous phase is eliminated . in addition , higher theoretical drug loading is achieved because the internal drug phase consists only of solid particles and not of a drug solution . in yet other embodiments , an o / w emulsion process may be used to incorporate the opioid antagonist into the microspheres . for the o / w dispersion method , the opioid antagonist is , dispersed in the polymer phase followed by emulsification in the external aqueous phase . the microspheres are then separated from the external aqueous phase by wet sieving , followed by washing and desiccator - drying . in certain embodiments , the present invention utilizes encapsulation techniques that allow liquid or solid substances to be encapsulated by polymers . in certain preferred embodiments , the opioid antagonist is in crystalline form . the crystalline opioid antagonist particles may be formed by solid - state crystallization via exposure to solvent vapors . the crystalline form may decrease the water content of the preparation , thus preserving the stability of the opioid antagonist . the crystal may be encapsulated in a fixed oil , and mixed with a solution of polymer and solvent in dispersion oil . u . s . pat . no . 6 , 287 , 693 to savoir describes stable shaped particles of crystalline organic compounds that are formed into microspheres and achieve storage stability . alternatively , any suitable method for producing crystalline particles of organic compounds can be used . the stability and release characteristics of emulsion devices are influenced by a number of factors such as the composition of the emulsion , droplet size , viscosity , phase volumes and ph . the encapsulation efficacy of the opioid antagonist can be optimized by minimizing the migration of drug from the polymer by altering the volume , temperature and chemical composition of the extraction medium ( quench solution ) during the encapsulation process . the purpose of the quench solution is to remove most of the organic solvent from the microspheres during processing . the quench liquid can be plain water , an aqueous solution , or other suitable liquid , the volume , amount , and type of which depends on the solvents in the emulsion phase . the quench liquid volume is on the order of 10 times the saturated volume ( i . e ., 10 times the quench volume needed to completely absorb the volume of solvent in the emulsion ). the quench volume can vary from about 2 to about 20 times the saturated volume . after quenching , the microspheres are separated from the aqueous quench solution by , e . g ., decantation or filtration with a sieve column . various other separation techniques can be used . residual solvent in the microspheres accelerates the degradation process , thereby reducing their shelf - life . the microspheres are therefore preferably washed with water or a solvent miscible therewith to further remove residual solvent , preferably to a level of about 0 . 2 to about 2 . 0 % or less . aliphatic alcohols such as methanol , ethanol , propanol , butanol , and isomers of the foregoing are preferred for use in the wash solution . most preferred is ethanol . alternatively , solvent removal can be accomplished by evaporation . in embodiments where the solvent evaporation method is used , the polymer can be dissolved in a volatile organic solvent . the opioid antagonist is dispersed or dissolved in a solution of the selected polymer and a volatile organic solvent like methylene chloride , the resultant dispersion or solution is suspended in an aqueous solution that contains a surface active agent such as poly ( vinyl alcohol ), and a temperature gradient is used to remove the solvent . the solvent evaporation method may involve dissolving the opioid antagonist and polymer in a co - solvent device . however , alternative methods may be used that omit the incorporation of unacceptable organic solvents . the resulting emulsion is stirred until most of the organic solvent is evaporated , leaving solid microspheres . the solution can be loaded with the opioid antagonist and suspended in 200 ml of vigorously stirred distilled water containing 1 % ( w / v ) poly ( vinyl alcohol ). after 4 hours of stirring , the organic solvent evaporates from the polymer , and the resulting microspheres can be washed with water and dried overnight in a lyophilizer . in embodiments where the spray - drying method is used , the polymer can be dissolved in methylene chloride . a known amount of drug is suspended ( where the opioid antagonist is insoluble ) or co - dissolved ( where the opioid antagonist is soluble ) in the polymer solution . the solution of the dispersion is then spray - dried . this method is used for small microspheres of between 1 - 10 microns . in certain embodiments , a hot melt encapsulation method may be used . using this method , the polymer may first be melted and then mixed with solid particles of drug that have been sieved to less than 50 microns . the mixture is suspended in a non - miscible solvent and , with continuous stirring , heated to 5 ° c . above the melting point of the polymer . once the emulsion is stabilized , it is cooled until the polymer particles solidify . the resulting microspheres are washed by decantation with petroleum ether to give a free - flowing powder . this technique is used for polyesters , polyanhydrides and polymers with high melting points and different molecular weights . the typical yield of microspheres in this process is about 80 - 90 %. the resulting microspheres have a core - shell structure . in order to create microspheres containing opioid antagonist , an organic or oil ( discontinuous ) phase and an aqueous phase may be combined . the organic and aqueous phases are largely or substantially immiscible , with the aqueous phase constituting the continuous phase of the emulsion . the organic phase includes the active agent and the wall forming polymer , i . e . the polymeric matrix material . the organic phase is prepared by dispersing the active opioid antagonist in the organic solvent ( s ). the organic and aqueous phases are preferably combined under the influence of a mixing means , preferably a static mixer . opioid antagonists useful in the present invention include , but are not limited to , nalorphine , nalorphine dinicotinate , naloxone , nalmephene , cyclazocine , levallorphan , naltrexone , nadide , cyclazocine , amiphenazole and pharmaceutically acceptable salts thereof and mixtures thereof . preferably , the opioid antagonist is an orally bioavailable antagonist , e . g ., naltrexone or pharmaceutically acceptable salt thereof . by utilizing a bioavailable antagonist , the transdermal device will deter both oral and parenteral abuse . after the formation of the microspheres containing the opioid antagonist , the microspheres are incorporated into a transdermal delivery device containing an opioid agonist . preferably , the microspheres are included in the transdermal delivery device so that they are substantially indistinguishable from the bulk of the opioid agonist - containing preparation ( e . g ., the microspheres can be imbedded in the matrix of the matrix delivery device ). in certain embodiments , the opioid agonist is in a form that can be absorbed through human skin , i . e ., the opioid agonist can be effectively administered via the transdermal route . in some embodiments , it may be necessary to further provide an absorption enhancer in order to facilitate transdermal absorption . in the transdermal delivery devices of the present invention , the opioid agonist is available for absorption , passing through pores in the intact skin surface of typically less than 50 nm to provide sustained therapeutic levels over a prolonged period . transdermal delivery devices that are prepared in accordance with the present invention may release the opioid agonist in accordance with first order pharmacokinetics ( e . g ., where the plasma concentrations of the opioid agonist increase over a specified time period ), or in accordance with zero order pharmacokinetics ( e . g ., where plasma concentrations are maintained at relatively constant level over a specified time period ), or with both first and zero order pharmacokinetics . opioid agonists that can be selected for use in the transdermal delivery devices of the present invention include any opioid agonists , mixed agonist - antagonists , or partial agonists , including but not limited to alfentanil , allylprodine , alphaprodine , anileridine , benzylmorphine , bezitramide , buprenorphine , butorphanol , clonitazene , codeine , desomorphine , dextromoramide , dezocine , diampromide , diamorphone , dihydrocodeine , dihydromorphine , dimenoxadol , dimepheptanol , dimethylthiambutene , dioxaphetyl butyrate , dipipanone , eptazocine , ethoheptazine , ethylmethylthiambutene , ethylmorphine , etonitazene , fentanyl , heroin , hydrocodone , hydromorphone , hydroxypethidine , isomethadone , ketobemidone , levorphanol , levophenacylmorphan , lofentanil , meperidine , meptazinol , metazocine , methadone , metopon , morphine , myrophine , narceine , nicomorphine , norlevorphanol , normethadone , nalorphine , nalbuphene , normorphine , norpipanone , opium , oxycodone , oxymorphone , papaveretum , pentazocine , phenadoxone , phenomorphan , phenazocine , phenoperidine , piminodine , piritramide , propheptazine , promedol , properidine , propoxyphene , remifentanil , sufentanil , tilidine , tramadol , pharmaceutically acceptable salts thereof , mixtures thereof ; and the like . in preferred embodiments , the opioid agonist is selected from the group consisting of transdermally administrable forms of fentanyl , buprenorphine , sufentanyl , hydrocodone , morphine , hydromorphone , oxycodone , codeine , levorphanol , meperidine , methadone , oxymorphone , dihydrocodeine , tramadol , pharmaceutically acceptable salts thereof , and mixtures thereof . any type of transdermal delivery device may be used in accordance with the methods of the present invention , as long as the desired pharmacokinetic and pharmacodynamic response ( s ) are attained over at least a 1 day period , e . g ., from 2 to 8 days . preferable transdermal delivery devices include , e . g ., transdermal patches , transdermal plasters , transdermal discs , and the like . in a preferred embodiment , the transdermal drug delivery device of the present invention is a patch , typically in the range of from about 1 to about 30 square centimeters , preferably 2 to 10 square centimeters . the term “ patch ” as used herein includes any product having a backing member and a pressure - sensitive adhesive face surface enabling adherence to the skin of a patient . such products can be provided in various sizes and configurations , such as tapes , bandages , sheets , and the like . in the transdermal delivery device of the present invention , the opioid agonist is preferably dispersed throughout a matrix ( e . g ., a polymer matrix ). in such a matrix device , release of the opioid agonist can be predominantly controlled by diffusion of the opioid agonist out of the polymer , or by erosion of the polymer to release the opioid agonist , or by a combination of these two mechanisms . when the diffusion of opioid agonist is faster than the erosion of the polymer , drug release is controlled by diffusion . when polymer erosion is faster than diffusion of the opioid agonist , drug release is controlled by erosion of the polymer . if the delivery device is prepared with a surface - erosion polymer , the release of drug can be controlled by varying the amount of drug loaded into the device and / or by varying the geometric dimension of the delivery device . generally , the polymers used in the polymer matrix of the transdermal delivery device are those capable of forming thin walls or coatings through which the opioid agonist can pass at a controlled rate . examples of such polymers for use in preparing the polymer matrix include polyethylene , polypropylene , ethylene / propylene copolymers , ethylene / ethylacrylate copolymers , ethylenevinyl acetate copolymers , silicones , rubber , rubber - like synthetic homo -, co - or block polymers , polyacrylic esters and the copolymers thereof ; polyurethanes , polyisobutylene , chlorinated polyethylene , polyvinylchloride , vinyl chloride - vinyl acetate copolymer , polymethacrylate polymer ( hydrogel ), polyvinylidene chloride , poly ( ethylene terephthalate ), ethylene - vinyl alcohol copolymer , ethylene - vinyloxyethanol copolymer , silicones including silicone copolymers such as polysiloxane - polymethacrylate copolymers , cellulose polymers ( e . g ., ethyl cellulose , and cellulose esters ), polycarbonates , polytetrafluoroethylene and mixtures thereof . preferred materials for use in preparing the polymer matrix are silicone elastomers of the general polydimethylsiloxane structures , ( e . g ., silicone polymers ). preferred silicone polymers are those that cross - link and are pharmaceutically acceptable . for example , preferred materials for use in preparing the polymer matrix layer include silicone polymers that are cross - linkable copolymers having dimethyl and / or dimethylvinyl siloxane units that can be crosslinked using a suitable peroxide catalyst . also preferred are those polymers consisting of block copolymers based on styrene and 1 , 3 - dienes ( particularly linear styrene - isoprene - block copolymers of styrene - butadiene - block copolymers ), polyisobutylenes , polymers based on acrylate and / or methacrylate . in certain embodiments , the polymer matrix includes a pharmaceutically acceptable cross - linking agent . suitable crosslinking agents include , e . g ., tetrapropoxysilane , among others . certain embodiments of the present invention include a polymer matrix layer comprising opioid agonist with intermixed microspheres of opioid antagonist . preferably , for the opioid antagonist to become bioavailable , the integrity of the microspheres must be disrupted . the combination of microsphere with polymer matrix prevents release of the opioid antagonist from the microspheres embedded within the matrix in an intact device . release of the opioid antagonist from microspheres may be further prevented by polymer coatings over the microspheres . preferably , the transdermal delivery device of the present invention comprises a backing layer made of a pharmaceutically acceptable material that is impermeable to the opioid agonist . the backing layer preferably serves as a protective cover for the opioid agonist and may also provide a support function . examples of materials suitable for making the backing layer are films of high and low density polyethylene , polypropylene , polyvinylchloride , polyurethane , polyesters such as poly ( ethylene phthalate ), metal foils , metal foil laminates of such suitable polymer films , and textile fabrics . preferably , the materials used for the backing layer are laminates of such polymer films with a metal foil such as aluminum foil . the backing layer can be any appropriate thickness that provides the desired protective and support functions . a suitable thickness will be , e . g ., from about 10 to about 200 microns . in certain alternative embodiments , the transdermal delivery device of the present invention can comprise microspheres are contained in a reservoir . in such a reservoir device , the opioid agonist and microspheres of opioid antagonist are dispersed in a reservoir ( e . g ., a liquid or gel reservoir ), and a rate limiting biodegradable membrane is situated in the flow path of the drugs , thereby limiting the flux of the opioid agonist to the skin . such a device can provide a constant release rate of opioid agonist , but serve to prevent release of the opioid antagonist . a transdermal delivery device utilizing a reservoir device can also have a backing layer , and optionally a removable protective layer as described above with the matrix device . preferred transdermal delivery devices used in accordance with the methods of the present invention preferably further include an adhesive layer to affix the delivery device to the skin of a patient for a desired period of administration , e . g ., from 2 to 8 days . if the adhesive layer of the delivery device fails to provide adequate adhesion for the desired period of time , it is possible to maintain contact between the delivery device and the skin by , e . g ., affixing the delivery device to the skin of the patient with adhesive tape , e . g ., surgical tape . it is not critical for purposes of the present invention whether adhesion of the delivery device to the skin of the patient is achieved solely by the adhesive layer of the delivery device or by use of an external adhesive source , such as surgical tape , provided that the delivery device is adhered to the patient &# 39 ; s skin for the requisite administration period . in all cases , however , the adhesive must allow for the patch to adhere firmly to the skin of the patient in need of treatment , but not be so strongly adhesive as to injure the patient when the patch is removed . the adhesive layer can be selected from any adhesive known in the art that is pharmaceutically compatible with the delivery device . the adhesive is preferably hypoallergenic . examples include a polyacrylic adhesive polymer , acrylate copolymer ( e . g ., polyacrylate ) or polyisobutylene adhesive polymer . other useful adhesives include silicones , polyisoalkylenes , rubbers , vinyl acetates , polybutadiene , styrene - butadiene ( or isoprene )- styrene block copolymer rubber , acrylic rubber and natural rubber ; vinyl - based high molecular weight materials such as polyvinyl alkyl ether , polyvinyl acetate ; cellulose derivatives such as methylcellulose , carboxymethyl cellulose and hydroxypropyl cellulose ; polysaccharides such as pullulan , dextrin and agar , and polyurethane elastomers and polyester elastomers . while many of these adhesives are virtually interchangeable , some combinations of a specific opioid analgesic and a specific adhesive may provide marginally better properties . in some embodiments , the adhesive is a pressure - sensitive contact adhesive , which is preferably hypoallergenic . in certain embodiments , the transdermal drug delivery material provides the functions of both drug - containing matrix and adhesive . in certain embodiments with a separate adhesive layer , the drug will be distributed throughout all the layers ( with the exception of the backing layer ) according to its relative affinity for the different environments offered by the different layers . the matrix “ layer ” may consist of more than a single sub - layer , with opioid loading in the different layers adjusted to optimize its delivery characteristics and opioid antagonist containing microspheres dispersed throughout . in such embodiments , the drug - containing matrix contacts the skin directly and the transdermal delivery device is held to the skin by a peripheral adhesive or the matrix itself . in certain embodiments , the transdermal delivery device of the present invention optionally includes a permeation - enhancing agent . permeation - enhancing agents are compounds that promote penetration and / or absorption of the opioid agonist through the skin into the blood stream of the patient . as a result of these penetration enhancers , almost any drug , to some degree , can be administered transdermally . permeation - enhancing agents are generally characterized to be from the group of monovalent branched or unbranched aliphatic , cycloaliphatic or aromatic alcohols of 4 - 12 carbon atoms ; cycloaliphatic or aromatic aldehydes or ketones of 4 - 10 carbon atoms , cycloalkanoyl amides of c 10 - 20 carbons , aliphatic , cycloaliphatic and aromatic esters , n , n - di - lower alkylsulfoxides , unsaturated oils , terpenes and glycol silicates . a non - limiting list of permeation - enhancing agents includes polyethylene glycols , surfactants , and the like . permeation of the opioid agonist can be also be enhanced by occlusion of the delivery device after application to the desired site on the patient with , e . g . an occlusive bandage . permeation can also be enhanced by removing hair from the application site by , e . g . clipping , shaving or use of a depilatory agent . another approach to enhancing permeation is by the application of heat to the site of the adhered patch , such as with an infrared lamp . other approaches to enhancing the permeation of opioid agonist includes the use of iontophoretic means . in certain embodiments , the transdermal delivery device includes a softening agent to modify the skin at the point of adhesion to promote drug absorption . suitable softening agents include higher alcohols such as dodecanol , undecanol , octanol , esters of carboxylic acids , wherein the alcohol component may also be a polyethoxylated alcohol , diesters of dicarboxylic acids , such as di - n - butyladiapate , and triglycerides particularly medium - chain triglycerides of the caprylic / capric acids or coconut oil . further examples of suitable softening agents are multivalent alcohols , e . g ., levulinic acid , caprylic acids , glycerol and 1 , 2 - propanediol , which can also be etherified by polyethylene glycols . in certain embodiments , a solvent for the opioid agonist is included in the transdermal delivery device of the present invention . preferably , the solvent dissolves the opioid agonist to a sufficient extent , thereby avoiding complete salt formation . a non - limiting list of suitable solvents includes those with at least one acidic group . monoesters of dicarboxylic acids such as monomethylglutarate and monomethyladipate are particularly suitable . other pharmaceutically acceptable compounds that may be included in the transdermal delivery device of the present invention include viscosity enhancing agents , such as cellulose derivatives , natural or synthetic gums , such as guar gum , and the like . in certain embodiments of the present invention , the transdermal delivery device further includes a removable protective layer . the removable protective layer is removed prior to application , and can consist of materials used for the production of the backing layer described above , provided that they are rendered removable , e . g ., by a silicone treatment . other examples of removable protective layers are polytetra - fluoroethylene , treated paper , allophane , polyvinyl chloride , and the like . generally , the removable protective layer is in contact with the adhesive layer , and provides a convenient means of maintaining the integrity of the adhesive layer until the desired time of application . it is well understood in the art of transdermal delivery devices that in order to maintain a desired flux rate for a desired dosing period , it is necessary to include an “ overage ” of active agent in the transdermal delivery device in an amount that is substantially greater than the amount to be delivered to the patient over the desired time period . for example , to maintain the desired flux rate for a three day time period , it is considered necessary to include in a transdermal delivery device much greater than what would otherwise be 100 % of a three - day dose of the active agent . the remainder of the active agent remains in the transdermal delivery device . only that portion of active agent that exits the transdermal delivery device becomes available for absorption into the skin . the term “ overage ” means for the purposes of the present invention the amount of opioid analgesic contained in a transdermal delivery device that is not delivered to the patient . the overage is necessary for creating a sufficient concentration gradient by which the active agent will migrate from the transdermal delivery device through a patient &# 39 ; s skin to produce a sufficient therapeutic effect . preferably , the transdermal delivery device of the present invention is used for prolonged dosing , releasing the opioid agonist in a constant or pulsed manner to the patient while the opioid antagonist contained in the microspheres remains unreleasable or substantially unreleasable . non - opioid analgesics that may be included in combination with the opioid agonist are , e . g ., acetaminophen , phenacetin and non - steroidal anti - inflammatory agents . suitable non - steroidal anti - inflammatory agents include aspirin , ibuprofen , diclofenac , naproxen , benoxaprofen , flurbiprofen , fenoprofen , flubufen , ketoprofen , indoprofen , piroprofen , carprofen , oxaprozin , pramoprofen , muroprofen , trioxaprofen , suprofen , aminoprofen , tiaprofenic acid , fluprofen , bucloxic acid , indomethacin , sulindac , tolmetin , zomepirac , tiopinac , zidometacin , acemetacin , fentiazac , clidanac , oxpinac , mefenamic acid , meclofenamic acid , flufenamic acid , niflumic acid tolfenamic acid , diflurisal , flufenisal , piroxicam , sudoxicam or isoxicam , pharmaceutically acceptable salts thereof ; and mixtures thereof . other suitable non - steroidal anti - inflammatory agents include cox - 2 inhibitors such as celecoxib , dup - 697 , flosulide , meloxicam , 6 - mna , l - 745337 , rofecoxib , nabumetone , nimesulide , ns - 398 , sc - 5766 , t - 614 , l - 768277 , gr - 253035 , jte - 522 , rs - 57067 - 000 , sc - 58125 , sc - 078 , pd - 138387 , ns - 398 , flosulide , d - 1367 , sc - 5766 , pd - 164387 , etoricoxib , valdecoxib , parecoxib , pharmaceutically acceptable salts thereof , and mixtures thereof . other active agents that may be combined with the opioid agonist can be , e . g , antiemetic / antivertigo agents such as chlorpromazine , perphenazine , triflupromazine , prochlorperazine , triethylperazine , metoclopropramide , cyclizine , meclizine , scopolamine , diphenhydramine , buclizine , dimenhydrate , and trimethobenzamide ; 5 - ht 3 receptor antagonists such as ondansetron , granisetron , and dolasetron ; anti - anxiety agents such as meprobamate , benzodiazepines , buspirone , hydroxyzine , and doxepin , and the like . it is contemplated that previously known transdermal delivery devices can be modified by including in the matrix , reservoir , and / or adhesive layers opioid - antagonist - containing microspheres as described above , so as to decrease the potential for abuse of such devices . for example , the transdermal delivery devices for use in accordance with the present invention can use certain aspects described in u . s . pat . no . 5 , 240 , 711 to hille , et . al . ; u . s . pat . no . 5 , 225 , 199 to hidaka et al . ; u . s . pat . no . 4 , 588 , 580 to gale et al . ; u . s . pat . no . 5 , 069 , 909 to sharma et al . ; u . s . pat . no . 4 , 806 , 341 to chien et al . ; u . s . pat . no . 5 , 026 , 556 to drust et al . ; and mcquinn , r . l . et al , “ sustained oral mucosal delivery in human volunteers ” j . controlled release ; ( 34 ) 1995 ( 243 - 250 ). the present invention is also directed to the transdermal dosage forms disclosed herein utilizing different active agent / antagonist combinations ( i . e . non - opioid ) in order to deter the abuse of the active agent . for example , when a benzodiazepine is used as the active agent in the transdermal dosage form of the present invention , a non - releasable benzodiazepine antagonist can be formulated in the transdermal dosage form . when a barbiturate is used as an active agent in the transdermal dosage form of the present invention , a non - releasable barbiturate antagonist can be formulated in the transdermal dosage form . when an amphetamine is used as an active agent in the transdermal dosage form of the present invention , a non - releasable amphetamine antagonist can be formulated in the transdermal dosage form . the term “ benzodiazepines ” refers to benzodiazepines and drugs that are derivatives of benzodiazepine that are able to depress the central nervous system . benzodiazepines include , but are not limited to , alprazolam , bromazepam , chlordiazepoxied , clorazepate , diazepam , estazolam , flurazepam , halazepam , ketazolam , lorazepam , nitrazepam , oxazepam , prazepam , quazepam , temazepam , triazolam , methylphenidate and mixtures thereof . benzodiazepine antagonists that can be used in the present invention include , but are not limited to , flumazenil . barbiturates refer to sedative - hypnotic drugs derived from barbituric acid ( 2 , 4 , 6 ,- trioxohexahydropyrimidine ). barbiturates include , but are not limited to , amobarbital , aprobarbotal , butabarbital , butalbital , methohexital , mephobarbital , metharbital , pentobarbital , phenobarbital , secobarbital and mixtures thereof . barbiturate antagonists that can be used in the present invention include , but are not limited to , amphetamines , as described herein . stimulants refer to drugs that stimulate the central nervous system . stimulants include , but are not limited to , amphetamines , such as amphetamine , dextroamphetamine resin complex , dextroamphetamine , methamphetamine , methylphenidate and mixtures thereof . stimulant antagonists that can be used in the present invention include , but are not limited to , benzodiazepines , as described herein . the present invention is also directed to the transdermal dosage forms disclosed herein utilizing adverse agents other than antagonists in order to deter the abuse of the active agent . the term “ adverse agent ” refers to any agent which can create an unpleasant effect upon administration in a releasable form . examples of adverse agents , other than antagonists , include emetics , irritants and bittering agents . irritants include , but are not limited to , capsaicin , capsaicin analogs , and mixtures thereof . capsaicin analogs include resiniferatoxin , tinyatoxin , heptanoylisobutylamide , heptanoyl guaiacylamide , other isobutylamides or guaiacylamides , dihydrocapsaicin , homovanillyl octylester , nonanoyl vanillylamide , and mixtures thereof . bittering agents include , but are not limited to , flavor oils ; flavoring aromatics ; oleoresins ; extracts derived from plants , leaves , flowers ; fruit flavors ; sucrose derivatives ; chlorosucrose derivatives ; quinine sulphate ; denatonium benzoate ; and combinations thereof the following examples are not meant to limit the invention in any manner . using the procedure disclosed in this example , multiple batches of naltrexone - loaded microspheres were prepared using different molecular weight lactide / glycolide ( 65 : 35 ) polymers ( 40 kd , 40 kd with 0 . 01 % calcium chloride , 50 : 50 blend of 40 kd and low molecular weight ( about 10 kd ) and 11 kd ) naltrexone - loaded microspheres were fabricated using a water - in - oil - in - water ( w / o / w ) double - emulsion solvent extraction / evaporation technique . in this process , naltrexone was dissolved in phosphate - buffered saline ( pbs ) ( ph 7 . 4 ) solution containing 0 . 05 % ( w / v ) polyvinylalcohol ( pva ) as an emulsifier and mixed with ethyl acetate containing poly ( lactic - co - glycolic acid ) ( plga ). the emulsification was carried out by sonication for 15 seconds . the resulting emulsion was further injected into pbs ( ph 7 . 4 ) containing 0 . 05 % ( w / v ) pva as an emulsifier to produce a double w / o / w emulsion . the dispersion was then stirred at a constant temperature for 30 minutes . in order to extract ethyl acetate from the first emulsion into the external phase , a second buffer solution ( ph 7 . 4 ) containing 0 . 05 % ( w / v ) pva was added continuously at a rate of 3 ml / minute . the temperature of the second emulsion throughout the solvent extraction / evaporation stage was maintained constant using a low - temperature circulator . the resulting naltrexone - loaded microspheres were collected by vacuum - filtration and washed three times with pbs . the microspheres were then vacuum - dried overnight and stored at 4 c . the load of naltrexone for the microspheres is set forth below in table 1 . the microsphere prepared in example 1 were exposed to simulated extraction conditions to determine the degree of in - vitro release of naltrexone from the microspheres . the extractions were performed using 0 . 5n nacl , ph 6 . 5 phosphate buffer . the sample size was 100 mg microspheres and the naltrexone release was measures at 0 . 5 , 1 and 4 hours . the results are set forth in table 2 and fig5 . based on the amount of antagonist released from any given microsphere formulation , the amount of antagonist loaded into the microspheres can be adjusted in order to obtain the release of a desired amount upon tampering . microspheres are prepared as follows . naltrexone is mixed with requisite amounts of gelatin , tween 80 and water , and heated . the mixture is then dispersed in a mixture of aluminum monostearate , span 80 and soybean oil to form a microemulsion . the microemulsion is homogenized by a microfluidizer . thereafter , the microemulsion is dispersed in a plga - acetonitrile solution . the acetonitrile is then removed from the emulsion by evaporation under atmospheric pressure , thereby forming microspheres containing naltrexone to be incorporated into a transdermal delivery device . a transdermal patch is prepared in accordance with the disclosure of wo 96 / 19975 to lts gmbh , published jul . 4 , 1996 , with the addition of naltrexone - containing microspheres prepared in accordance with example 1 , as follows : the following are homogenized : 1 . 139 g of a 47 . 83 w / w % polyacrylate solution with a self cross - linking acrylate copolymer containing 2 - ethylhexylacrylate , vinyl acetate , acrylic acid ( dissolving agent : ethylacetate : heptan : isopropanol : toluol : acetylacetonate in the ratio of 37 : 26 : 26 : 4 : 1 ), 100 g laevulinic acid , 150 g oleyloleate , 100 g polyvinylpyrrolidone , 150 g ethanol , 200 g ethyl acetate and 100 g buprenorphine base . the mixture is stirred for about 2 hours and then examined visually to confirm that all solid substances have been dissolved . evaporation loss is controlled by method of weighing back and making up for the solvent with addition of of ethylacetate , if necessary . thereafter , the mixture is combined with the naltrexone microspheres prepared as described above in example 1 . this mixture is then transferred to a 420 mm wide transparent polyester foil . the solvent is removed by drying with heated air . thereafter , the sealing film is covered with a polyester foil . a surface of about 16 cm 2 is cut with the help of the appropriate cutting tool . while the invention has been described and illustrated with reference to certain preferred embodiments thereof , those skilled in the art will appreciate that modifications can be made herein without departing from the spirit and scope of the invention . such variations are contemplated to be within the scope of the appended claims .
the present invention provides abuse - resistant transdermal delivery devices containing an opioid agonist intended for analgesic purposes in pain patients .