TAMPER-RESISTANT ORAL OPIOID AGONIST FORMULATIONS

Abstract: Disclosed is an oral dosage form comprising (i) an opioid agonist in releasable form and (ii) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio of the amount of antagonist released from said dosage form after tampering to the amount of said antagonist released from said intact dosage form is about 4:1 or greater, based on the in-vitro dissolution at 1 hour of said dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 rpm at 37 degrees C wherein said agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers.

Description: T MPER-RESISTANT ORAL OPIOID AGONIST FORMULATIONS Opioids, also known as opioid agonists, are a group of drugs that exhibit opium or morphme-like properties The opioids are employed primarily as moderate to strong analgesics, but e many other pharmacological effects as well, including diowsmess, respiratoiΛ depression, changes in mood and mental clouding w ithout a resulting loss of consciousness Opioids act as agonists, interacting with stereospecific and saturable binding sites in the bram and other tissues Endogenous opioid-hke peptides aie piesent paiticularly in areas of the central nervous system that are presumed to be related to the perception of pain, to movement, mood and behavior, and to the regulation of neuroendocπnological functions Opium contains more than twenty distinct alkaloids Morphine, codeine and papavenne are included in this group By the middle ofthe nineteenth century, the use of pure alkaloids such as morphine rather than crude opium preparations began to spread throughout the medical world Parenteral use of morphine tended to produce a more severe variety of compulsive drug use than crude opium preparations The problem of addiction to opioids stimulated a search for potent analgesics that would be free ofthe potential to produce addiction By 1967, researchers had concluded that the complex interactions among morphme-like drugs, antagonists, and what was then called "mixed agonist-antagonist" could best be explained b\ postulating the existence of more than one type of receptoi foi opioids and related diugs With the advent of new totally synthetic entities with morphme-like actions, the term 'opioid was generally retained as a generic designation for all exogenous substances that bind stereo specifically to any of several subspecies of opioid receptors and produce agonist actions While this greater understanding advanced the science of pharmacology, it did not lesult m the development of an analgesic opioid free of abuse potential The potential for the development of tolerance and physical dependence with repeated opioid use is a characteristic feature of all the opioid drugs, and the possibility of developing psychological dependence (I e , addiction) is one of the major concerns in the use ofthe treatment of pain with opioids, even though latrogemc addiction is rare Another major concern associated with the use of opioids is the diversion of these drugs from the patient m pain to another (non-patient) for illicit purposes, e g , to an addict The overall abuse potential of an opioid is not established by any one single factor. Instead, there is a composite of factors, including, the capacity ofthe drug to produce the kind of physical dependence in which drug withdrawal causes sufficient distress to bring about drug-seeking behavior; the ability to suppress withdrawal symptoms caused by withdrawal from other agents; the degree to which it induces euphoria similar to that produced by morphine and other opioids; the patterns of toxicity that occur when the drug is dosed above its normal therapeutic range; and physical characteristics ofthe drugs such as water solubility. Such physical characteristics may determine whether the drug is likely to be abused by the parenteral route. In the United States, the effort to control the compulsive drug user includes efforts to control drug availability by placing restrictions on the use of opioids in the treatment of pain of compulsive drug users. In practice, the physician is often faced with a choice of administering potent opioid analgesics even to persons who seem predisposed to develop psychological dependence, i.e., addiction, on such drugs. In view of this problem, it has been recommended that these patients should not be given an opioid when another drug without a potential for abuse will suffice; and further that these patients should not be provided with a dosage form which may be parenterally abused and should only be given a few days' supply at any one time. At least three basic patterns of opioid use and dependence have been identified. The first involves individuals whose drug use begins in the context of medical treatment and who obtain their initial supplies through legitimate sources, e.g., physicians. Another pattern begins with experimental or "recreational" drug use and progresses to more intensive use. A third pattern involves users who begin in one or another ofthe preceding patterns, but later switch to oral opioids such as methadone, obtained from licensed addiction treatment programs. Tolerance refers to the need to increase the dose of opioid over a period of time in order to achieve the same level of analgesia or euphoria, or the observation that repeated administration ofthe same dose results in decreased analgesia, euphoria, or other opioid effects. It has been found that a remarkable degree of tolerance develops to the respiratory %~ depressant, analgesic, sedative, emetic and euphorigenic effects of opioids. However, the rate at which this tolerance may develop in either an addict or in a patient requiring treatment of pain depends on the pattern of use. If the opioid is used frequently, it may be necessary to increase the dose. Tolerance does not develop equally or at the same rate to all the effects of opioids, and even users who are highly tolerant to respiratory depressant effects continue to exhibit miosis and constipation. Tolerance to opioids largely disappears when the withdrawal syndrome has been completed. Physical dependence may develop upon repeated administrations or extended use of opioids. Physical dependence is gradually manifested after stopping opioid use or is precipitously manifested (e.g., within a few minutes) after administration of a narcotic antagonist (referred to "precipitated withdrawal"). Depending upon the drug to which dependence has been established and the duration of use and dose, symptoms of withdrawal vary in number and kind, duration and severity. The most common symptoms of the withdrawal syndrome include anorexia, weight loss, pupillary dilation, chills alternating with excessive sweating, abdominal cramps, nausea, vomiting, muscle spasms, hyperirritability, lacrimation, rinorrhea, goose flesh and increased heart rate. Natural abstinence syndromes typically begin to occur 24-48 hours after the last dose, reach maximum intensity about the third day and may not begin to decrease until the third week. Precipitated abstinence syndromes produced by administration of an opioid antagonist vary in intensity and duration with the dose and the specific antagonist, but generally vary from a few minutes to several hours in length. Psychological dependence (i.e., addiction) on opioids is characterized by drug-seeking behavior directed toward achieving euphoria and escape from, e.g., psychosocioeconomic pressures. An addict will continue to administer opioids for non-medicinal purposes and in the face of self-harm. There have previously been attempts in the art to control the abuse potential associated with opioid analgesics. For example, the combination of pentazocine and naloxone has been utilized in tablets available in the United States, commercially available as Talwin^Nx from Sanofi-Winthrop. Talwin^Nx contains pentazocine hydrochloride equivalent to 50 mg base and naloxone hydrochloride equivalent to 0.5 mg base. Talwin Nx is indicated for the relief of moderate to severe pam The amount of naloxone present m this combination has low activity when taken orally, and minimally interferes with the pharmacologic action of pentazocine Howe\ er. this amount of naloxone given parenterally has profound antagonistic action to naicotic analgesics Thus, the inclusion of naloxone is intended to curb a form of misuse of oral pentazocine which occurs when the dosage form is solubihzed and injected Therefore, this dosage has lower potential for parenteial misuse than previous oral pentazocine formulations However, it is still subject to patient misuse and abuse by the oial route, for example, by the patient taking multiple doses at once A fixed combination therapy comprising tilidme (50 mg) and naloxone (4 mg) has been available m Germany for the management of severe pam since 1978 (Valoron N, Goedecke) The rationale for the combination of these drugs is effective pain relief and the prevention of tilidme addiction through naloxone-mduced antagonisms at the morphine receptor A fixed combination of buprenorphme and naloxone was introduced m 1991 in New Zealand (Temgesic Nx, Reckitt & Colman) for the treatment of pam OBJECTS AND SUMMARY OF THE INVENTION It is an object ofthe invention to provide an oral dosage form of an opioid agonist that is useful for decreasing the potential for abuse ofthe opioid agonist contained therein It is an object of a preferred embodiment ofthe mvention to provide an oral dosage form of an opioid agonist that is useful for decreasing the potential abuse of the opioid agonist without affecting the analgesic effects of the opioid agonist or incurring the nsk of precipitating withdrawal. It is an object of a preferred embodiment ofthe invention to provide an oral dosage form of an opioid agonist that is resistant to misuse, abuse or diversion, wherein said resistance does not depend on individual patient-specific differences m the effects of co- admimstered opioid agonist and antagonist mixtures It is an object of a preferred embodiment ofthe invention to provide an oral dosage form containing an effective dose of an opioid agonist along with a dose of opioid antagonist which does not change the analgesic efficacy ofthe opioid agonist when the dosage form is orally administered intact, but which can prevent abuse if the dosage form is tampered with by interfering with the effect ofthe opioid agonist It is an object of a preferred embodiment ofthe invention to provide a method for preventing abuse of an oral opioid dosage form where the dosage form also mcludes a dose of opioid antagonist which is sequestered, e g , is not when the dose is administered intact but is bioavailable when the dosage form is tampered with (e g , m an attempt to misuse the dose of opioid analgesic) It is a further object of a preferred embodiment of the invention to piovide oial dosage forms that are intended for or are suitable for use m the management of acute or chronic pam where alteration of the opioid agonist's analgesic affects must be avoided such as in cases of tolerance, physical dependence or individual variability m hepatic metabolism or physiolog} It is a further object of a preferred embodiment ofthe invention to provide a method of treating pam m human patients with an oral dosage form of an opioid agonist while reducing its misuse by oral, parenteral, mtranasal and/or sublmgual route Some or all ofthe above objects and others are achieved by embodiments ofthe present invention, which is directed m part to an oral dosage form comprising an opioid agonist and an opioid antagonist, wherein the opioid antagonist is present m a substantially non-releasable form (I e , "sequestered") In piefened embodiments, the dosage form contains an orally therapeutically effective amount of the opioid agonist, the dosage form providing a desired analgesic effect Because the opioid antagonist is present in a substantially non-releasable form, it does not substantially block the analgesic effect ofthe opioid agonist when the dosage form is orally administered intact, and does not pose a risk of precipitation of withdrawal m opioid tolerant or dependent patients In preferred embodiments, the oral dosage form of the present invention is directed to an oral dosage form compnsing (l) an opioid agonist m releasable form and (n) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio ofthe amount of antagonist released from the dosage form after tampering to the amount ofthe antagonist released from the intact dosage form is about 4 1 or greater, based on the m-vitro dissolution at 1 hour ofthe dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 rpm at 37 degrees C wherein the agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers In other embodiments, the invention is directed to an oral dosage form comprising (I) an opioid agonist in releasable form and (π) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio of the amount of antagonist released from the dosage form after tampering to the amount of the antagonist released from the intact dosage form is about 4 1 or greater, based on the m-vitro dissolution at 1 hour ofthe dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 rpm at 37 degrees C wherein the antagonist is m the form of multiparticulates individually coated with a sequestering material which substantially prevents release ofthe antagonist In other embodiments, the mvention is directed to an oral dosage form comprising (l) an opioid agonist in releasable form and (n) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio of the amount of antagonist released from the dosage form after tampeπng to the amount of the antagonist released from the intact dosage form is about 4 1 or greater, based on the m-vitio dissolution at 1 hour ofthe dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 rpm at 37 degrees C wherein the antagonist is dispersed m a matrix composing a sequesteπng matenal which substantially prevents the release of the antagonist In other embodiments, the invention is directed to an oral dosage form comprising (l) an opioid agonist in releasable form and (n) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio of the amount of antagonist contained in the intact dosage form to the amount of the antagonist released from the mtact dosage form after 1 hour is about 4 1 or greater, based on the m-vitro dissolution at 1 hour ofthe dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 rpm at 37 degrees C wherein the agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers ' In other embodiments, the invention is directed to an oral dosage form comprising (1) an opioid agonist in a releasable form, and (n) a sequestered opioid antagonist which is substantially not released when the dosage form is administered mtact, such that the amount of antagonist released from the mtact dosage form after 1 hour is less than an amount bioequivalent to 0 25 mg naltrexone and the amount of the antagonist released after 1 hour from the dosage fonn after tampenng is an amount bioequivalent to 0 25 mg naltrexone or more, the release based on the dissolution at 1 hour ofthe dosage form m 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C, wherein the agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers Preferably, the amount of antagonist released after 1 hour from the tampered dosage form is an amount bioequivalent to about 0 5 mg naltrexone or more and/or the amount of antagonist released after 1 hour from the intact dosage form is an amount bioequivalent to about 0 125 mg naltrexone or less In other embodiments, the invention is directed to an oral dosage form comprising (i) an opioid agonist in a releasable form, and (n) sequestered naltrexone or a pharmaceutically acceptable sat thereof which is substantially not released when the dosage form is administered intact, such that the amount of naltexone released from the mtact dosage form after 1 hour is less than 0 25 mg and the amount ofthe naltrexone released after 1 hour from the dosage form after tampering is 0 25 mg or more, the release based on the dissolution at 1 hour ofthe dosage form m 900 ml of Simulated Gastnc Fluid using a USP Type II (paddle) apparatus at 75 m at 37 degrees C, wherein the agonist and naltrexone are interdispersed and are not isolated from each other in two distinct layers Alternatively m this embodiment, the oral the amount of antagonist released after 1 hour from the tampered dosage form is about 0 5 mg naltrexone or more and/or the amount of antagonist released after 1 hour from the mtact dosage form rs about 0 125 mg naltrexone or less In other embodiments, the invention is directed to an oral dosage form comprising (I) a therapeutic effect of an opioid agonist, and (n) a sequestered opioid antagonist, such that at 1 hour after oral administration, the mtact dosage form releases not more than about 25% of the antagonist, the dosage form providing analgesia and the released antagonist not affecting analgesic efficacy, wherein the agonist and antagonist are interdispersed and are not isolated from each other m two distinct layers Preferabl , the mtact dosage form releases not more than about 12 5% ofthe antagonist In other embodiments, the invention is directed to an oial dosage form compnsing (i) an opioid agonist m a releasable form, and an (n) opioid antagonist in substantially non- releasable form wherein the antagonist is in the form of multiparticulates ldually coated with a material which substantially prevents release of the antagonist In other embodiments, the mvention is directed to an oial dosage form compnsing (I) an opioid agonist in a releasable form, and an (n) opioid antagonist m substantially non- releasable form wherein the antagonist is dispersed m a matrix comprising a material which substantially prevents the release ofthe antagonist In certain embodiments ofthe invention, the mtact dosage form of the present invention releases some of the opioid antagonist contained therein at 1 hour after oral administration, e g , the dosage form releases at least 0 025 mg naltrexone or a bioequivalent dose of another antagonist at 1 hour In these embodiments, the dosage form provides analgesia to the patient and the released antagonist does not affect analgesic efficacy In these embodiments, the dosage form preferably does not release 0 25 mg or more naltrexone at 1 hour after administration The release of naltrexone from the mtact dosage fonn may be measured for puφoses of these embodiments, based on the m-vitro dissolution of the dosage form at 1 hour in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) appaiatus at 75 φm at 37 degrees C In other embodiments, the invention is directed to an oral dosage form comprising an opioid agonist and naltrexone or a salt thereof in a substantially non-releasable form,wherem the agonist and naltrexone are at least partrally mterdrspersed In other embodrments, the invention is directed to an oral dosage form comprising an opioid agonist, and an orally-bioavailable opioid antagonist in a substantially non-releasable form, wherein the agonist and antagonist are at least partially interdispersed In embodiments ofthe invention wherein the antagonist is in the form of multiparticulates coated with a sequestering material, the multiparticulates can be in the fonri of inert beads coated with the antagonist and overcoated with the material, or alternate ely m the fom of a granulation comprising the antagonist and the material The multiparticulates can be dispersed m a matrix comprising the opioid agonist or contained in a capsule w ith the opioid agonist In embodiments of the invention wherein the antagonist is dispersed in a matrix comprising a sequestering material which substantially prevents the release of the antagonist the matrix can be m the form of pellets The pellets can be dispersed in another matrix comprising the opioid agonist or contained m a capsule with the opioid agonist In other embodiments ofthe invention, part of the antagonist is m a matrix and oi pail ofthe antagonist is in a coated bead In certain embodiments ofthe invention which exhibit the above-disclosed ratio of about 4 1 or greater concerning the amount of antagonist released from the dosage fonri after tampenng to the amount of said antagonist released from the mtact dosage fonri based on the dissolution at 1 hour ofthe dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C, the mtact dosage form releases 22 5% or less ofthe antagonist after 1 hour and the tampered dosage form releases 90% or more antagonist after 1 hour In another embodiment, the intact dosage form releases 20% or less of said antagonist after 1 hour and the tampered dosage form releases 80%o or more antagonist after 1 hour In another embodiment, the mtact dosage fonri releases 10% or less of said antagonist after 1 hour and the tampered dosage fonri releases 40% or more antagonist aftei 1 hour In another embodiment the mtact dosage form releases 5% or less of said antagonist after 1 hour and the tampered dosage form releases 20%o or more antagonist after 1 hour In certain embodiments ofthe invention, the ratio ofthe amount of antagonist released from the dosage form after tampering to the amount of said antagonist released from the mtact dosage form based on the dissolution at 1 hour ofthe dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C is 10 1 or greater, 50 1 or greater or 100 1 or greater In certain embodiments of the invention, the antagonist is naltrexone or a pharmaceutically acceptable salt thereof. In such embodiments, the intact dosage form preferably releases less than 0.25 mg, preferably 0.125 mg or less naltrexone at 1 hour according to the above dissolution conditions. Preferably, the tampered dosage form releases 0.25 mg or more naltrexone at 1 hour under the same conditions. In certain embodiments of the invention, the ratio ofthe amount of antagonist released from the dosage form after tampering to the amount of said antagonist released from the intact dosage form based on the dissolution at 1 hour ofthe dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C is 10:1 or greater, 50:1 or greater or 100:1 or greater. In certain embodiments ofthe dosage form the antagonist in a substantially non- releasable form is adapted to release less than 15% by weight in vivo after 36 hours. In certain embodiments ofthe dosage form the antagonist in a substantially non-releasable form is adapted to release less than 8% by weight in vivo after 36 hours. In certain embodiments of the dosage form the antagonist in a substantially non-releasable form is adapted to release less than 3%by weight in vivo after 36 hours. In certain embodiments of the dosage form the antagonist in a substantially non-releasable form is adapted to release less than 1% by weight in vivo after 36 hours. In certain embodiments ofthe dosage form the antagonist in a substantially non-releasable form is adapted to release less than .5% by weight in vivo after 36 hours. The invention is also directed to methods of preventing abuse of an opioid agonist utilizing the dosage forms disclosed herein. The method can comprise providing the opioid agonist in an oral dosage form together with an opioid antagonist, wherein the opioid antagonist is present in a form which is in a substantially non-releasable foπn upon digestion when the integrity ofthe dosage form is maintained until digestion begins, but which becomes bioavialable if subjected to tampering (e.g., crushing, shear forces which break up the dosage form, etc., solvents or temperatures of greater than 45°C). Another embodiment ofthe invention is directed to a method of decreasing the abuse of an opioid agonist in an oral dosage form, comprising preparing an oral dosage form as disclosed herein. For example, the method can comprise preparing a dosage form which comprises (i) an orally therapeutically effective amount of an opioid agonist and (ii) an opioid antagonist in a substantially non-releasable form such that said dosage form provides a desired analgesic effect and said antagonist does not substantially block the analgesic effect ofthe opioid agonist when said dosage form is administered orally intact. In alternative embodiments, the effect of the opioid agonist is at least partially blocked when said dosage form tampered with, e.g., chewed, crushed or dissolved in a solvent, and administered oralh', intranasally, parenterally or sublingually. The invention is also directed to a method of treating pain with the dosage forms disclosed herein. The method can comprise providing an oral dosage form containing an opioid agonist in a releasable form and an opioid antagonist in substantially non-releasable form; and orally administering the intact oral dosage form. Another embodiment ofthe invention is directed to a method of treating pain with the disclosed dosage forms. In certain embodiments, the method of treating pain in patients with a dosage form having less abuse potential comprises providing an oral dosage form containing a releasable form of an opioid agonist and a substantially non-releasable form of an opioid antagonist; and orally administering the oral dosage form to provide a blood plasma level of agonist greater than the minimum analgesic concentration ofthe opioid agonist. The invention is also directed to methods of preparing the dosage forms disclosed herein. In certain embodiments, the invention comprises a method of preparing an oral dosage form comprising pretreating an opioid antagonist to render it substantially non- releasable; and combining the pretreated antagonist with a releasable form of an opioid agonist in a manner that maintains the integrity ofthe non-releasable form ofthe antagonist. Certain embodiments ofthe invention are directed to formulations wherein the agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers. However in certain embodiments, the agonist and antagonist are partially interdispersed The term "analgesic effectiveness" is defined for puφoses ofthe present invention as a satisfactory reduction in or elimination of pain, along with a tolerable level of side effects, as determined by the human patient. The phrase "not substantially blocking the analgesic K effect of an opioid agonist" means that the opioid antagonist does not block the effects ofthe opioid agonist m sufficient degree as to render the dosage form therapeutically less effective for providing analgesia The phrase "risk of precipitation of withdrawal" means that the proper action of the formulation does not depend on a specific ratio of agonist to antagonist 01 differential metabolism of either The term "an opioid antagonist in a substantially non-releasable form" lefers to an opioid antagonist that is not released or substantially not released at one hour after the mtact dosage form containing both opioid agonist and the opioid antagonist is orally administered (1 e , without having been tampered with) For puφoses of the invention, the amount leleased after oral administration of the mtact dosage form may be measured in- vitro \ la the dissolution at 1 hour of the dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C Such a dosage form is also refened to as comprising a "sequestered antagonist" Although the preferred embodiments ofthe invention comprise an opioid antagonist in a form that completely prevents the release of the opioid antagonist, the invention also includes an antagonist in a substantially non-releasable form The term "substantially not released" refers to the antagonist that might be released in a small amount, as long as the amount released is not affect or does not significantly affect analgesic efficacy w hen the dosage form is orally administered to humans as intended In certain preferred embodiments ofthe invention, the substantially non-ieleasable form ofthe antagonist is resistant to laxatives (e g , mineral oil) used to manage delayed colonic transit and to achlorhydπc states In certain embodiments, the substantially non-releasable form of an opioid antagonist comprises an opioid antagonist that is formulated with one or more of pharmaceutically acceptable hydrophobic material, such that the antagonist is not released or substantially not released dunng its transit through the gastrointestinal tract when administered orally as intended, without having been tampered with In certain embodiments ofthe present invention, the substantially non-releasable form \X ofthe opioid antagonist is vulnerable to mechanical, thermal and/or chemical tampering, e g , tampenng by means of crushing, sheanng, gnndmg, chewing and/or dissolution in a solvent in combination with heating (e g , greater than about 45°C) ofthe oral dosage form When thus tampered with, the integrity ofthe substantially non-releasable form ofthe opioid antagonist will be compromised, and the opioid antagonist will be made available to be released In certain embodiments, when the dosage form is chewed, crushed or dissolved and heated in a solvent, and administered orally, intranasally, parenterally or subhngually, the analgesic or euphoric effect of the opioid is reduced or eliminated In certain embodiments, the effect ofthe opioid agonist is at least partially blocked by the opioid antagonist In certain other embodiments, the effect ofthe opioid agonist is substantially blocked by the opioid antagonist The term "tampering" means any manipulation by mechanical, thenrial and/oi chemical means which changes the physical properties ofthe dosage form, e g , to liberate the opioid agonist for immediate release if it is m sustained release form, or to make the opioid agonist available for inappropriate use such as administration by an alternate route, e g , parenterally The tampering can be, e g , by means of crushing, shearing, grinding, chewing, dissolution m a solvent, heating (e g , greater than about 45°C), or any combination thereof The term "at least partially blocking the opioid effect," is defined for puφoses of the present invention to mean that the opioid antagonist at least significantly blocks the euphoric effect ofthe opioid agonist, thereby reducing the potential for abuse of the opioid agonist in the dosage form In certain preferred embodrments of the present invention, the substantially non- releasable form ofthe opioid antagonist compnses opioid antagonist particles m a coating that substantially prevents the release ofthe antagonist In prefened embodiments, the coating comprising one or more of pharmaceutically acceptable hydrophobic material The coating is preferably impermeable to the opioid antagonist contained therein and is insoluble in the gastrointestinal system, thus substantially preventing the lelease ofthe opioid antagonist when the dosage form is administered orally as intended Accordingly, when the oral dosage form is not tampered with as to compromise the integrity ofthe coating, the opioid antagonist contained therein will not be substantially released during its first hour of transit through the gastrointestinal system, and thus would not be available for absoφtion. In certain preferred embodiments ofthe present invention, the hydrophobic material comprises a cellulose polymer or an acrylic polymer that is insoluble in the gastrointestinal fluids and impermeable to the opioid antagonist. The term "particles" of opioid antagonist, as used herein, refers to granules, spheroids, beads or pellets comprising the opioid antagonist. In certain preferred embodiments, the opioid antagonist particles are about 0.2 to about 2 mm in diameter, more preferably about 0.5 to about 2 mm in diameter. In certain embodiments of the present invention, the oral dosage form further comprises an opioid antagonist in a releasable form and is thus capable of being released from the oral dosage form when orally administered, the ratio ofthe opioid agonist to the releasable form ofthe opioid antagonist being such that the dosage fonri, when administered orally, is analgesically effective. For example, when the opioid antagonist is coated with a coating that substantially prevents its release, and is then mixed with an opioid agonist and compressed into tablets, certain amounts ofthe coating might be cracked, thus exposing the opioid antagonist to be released upon oral administration. Preferably, the opioid agonist useful for the present invention may be selected from the group consisting of moφhine, hydromoφhone, hydrocodone, oxycodone, codeine, levoφhanol, meperidine, methadone and mixtures thereof. Preferred examples ofthe opioid antagonist useful for the present invention includes naltrexone, naloxone. nalmefene, cyclazacine, levalloφhan, pharmaceutically acceptable salts thereof and mixtures thereof. In certain embodiments ofthe present invention, the ratio ofthe opioid agonist and the opioid antagonist, present in a substantially non-releasable form, is about 1 :1 to about 50:1 by weight, preferably about 1 : 1 to about 20: 1 by weight or 15: 1 to about 30: 1. The weight ratio ofthe opioid agonist to opioid antagonist, as used in this application, refers to the weight of the active ingredients. Thus, for example, the weight ofthe opioid antagonist excludes the weight ofthe coating or matrix that renders the opioid antagonist substantially non-releasable, or other possible excipients associated with the antagonist particles. In certain preferred embodiments, the ratio is about 1:1 to about 10: 1 by weight. Since the opioid antagonist is m a substantially non-releasable from, the amount of such antagonist within the dosage form may be varied more widely than the opioid agonist/antagonist combination dosage forms where both are available for release upon administration as the formulation does not depend on differential metabolism or hepatic clearance for proper functioning. For safety reasons, the amount of the opioid antagonist present in a substantially non-releasable form is selected as not to be harmful to humans even if fully released by tampering with the dosage fonri. In certain preferred embodiments ofthe present invention, the opioid agonist comprises hydrocodone, oxycodone or pharmaceutically acceptable salts thereof and the opioid antagonist, present in a substantially non-releasable form, comprises naloxone, naltrexone or pharmaceutically acceptable salts thereof. The oral dosage form containing an opioid agonist in combination with a substantially non-releasable form of an opioid antagonist includes, but are not limited to, tablets or capsules. The dosage forms ofthe present invention may include any desired pharmaceutical excipients known to those skilled in the art. The oral dosage forms may further provide an immediate release ofthe opioid agonist. In certain embodiments, the oral dosage forms ofthe present invention provide a sustained release ofthe opioid agonist contained therein. Oral dosage forms providing sustained release ofthe opioid agonist may be prepared in accordance with formulations/methods of manufacture known to those skilled in the art of pharmaceutical formulation, e.g., via the incoφoration of a sustained release carrier into a matrix containing the substantially non-releasable form of an opioid antagonist; or via a sustained release coating of a matrix containing the opioid agonist and the substantially non-releasable form of the opioid antagonist. The benefits of the abuse-resistant dosage form are especially great in connection with oral dosage forms of strong opioid agonists (e.g., oxycodone or hydrocodone), which provide valuable analgesics but are prone to being abused. This is particularly true for sustained release opioid agonist products which have a large dose of a desirable opioid agonist intended to be released over a period of time in each dosage unit. Drug abusers take such sustained- release product and crush, grind, extract or otherwise damage the product so that the full contents ofthe dosage form become available for immediate absoφtion. Since such tampering ofthe dosage form ofthe invention results in the opioid antagonist also becoming available for absoφtion, the present invention provides a means for frustrating such abuse. In addition, the present invention addresses the risk of overdose to ordinary patients from "dumping" effect of the full dose ofthe opioid agonist if the product is accidentally chewed or crushed. The term "sustained release" is defined for puφoses of the present invention as the release ofthe opioid agonist from the oral dosage form at such a rate that blood (e.g., plasma) concentrations (levels) are maintained within the therapeutic range (above the minimum effective analgesic concentration or "MEAC") but below toxic levels over a period of 8 to 24 hours, preferable over a period of time indicative of a twice-a-day or a once-a-day formulation. The invention may provide for a safer product (e.g., less respiratory depression), if the product is misused, as well as one with less risk of abuse. In certain embodiments, a combination of two opioid agonists is included in the formulation. In further embodiments, one or more opioid agonist is included and a further non-opioid drug is also included. Such non-opioid drugs would preferably provide additional analgesia, and include, for example, aspirin, acetaminophen, non-steroidal anti-inflammatory drugs ("NSAIDS"), NMDA antagonists, and cycooxygenase-II inhibitors ("COX-II inhibitors"). In yet further embodiments, a non-opioid drug can be included which provides a desired effect other than analgesia, e.g., antitussive, expectorant, decongestant, or antihistamine drugs, and the like. For puφoses ofthe present invention, the term "opioid agonist" is interchangeable with the term "opioid" or "opioid analgesic" and shall include combinations of more than one opioid agonist, and also include the base ofthe opioid, mixed agonist-antagonists, partial agonists, pharmaceutically acceptable salts thereof, stereoisomers thereof, ethers and esters thereof, and mixtures thereof. For puφoses of the present invention, the term "opioid antagonist" shall include combinations of more than one opioid antagonist, and also include the base, pharmaceutically acceptable salts thereof, stereoisomers thereof, ethers and esters thereof, and mixtures thereof. The invention disclosed herein is meant to encompass all pharmaceutically acceptable salts thereof of the disclosed opioid agonists and antagonists. The pharmaceutically acceptable salts include, but are not limited to, metal salts such as sodium salt, potassium salt, secium salt and the like; alkaline earth metals such as calcium salt, magnesium salt and the like; organic amine salts such as triethylamine salt, pyridine salt, picoline salt, ethanolamine salt, triethanolamine salt, dicyclohexylamine salt, N,N'-dibenzylethylenediamine salt and the like; inorganic acid salts such as hydrochloride, hydrobromide, sulfate, phosphate and the like; organic acid salts such as formate, acetate, trifiuoroacetate, maleate, tartrate and the like; sulfonates such as methanesulfonate, benzenesulfonate, p-toluenesulfonate. and the like; amino acid salts such as arginate, asparginate, glutamate and the like. Some ofthe opioid agonists and antagonists disclosed herein may contain one or more asymmetric centers and may thus give rise to enantiomers, diastereomers, and other stereoisomeric forms. The present invention is also meant to encompass all such possible forms as well as their racemic and resolved forms and mixtures thereof. When the compounds described herein contain olefinic double bonds or other centers of geometric asymmetry, and unless specified otherwise, it is intended to include both E and Z geometric isomers. All tautomers are intended to be encompassed by the present invention as well. As used herein, the term "stereoisomers" is a general term for all isomers of individual molecules that differ only in the orientation of their atoms is space. It includes enantiomers and isomers of compounds with more than one chiral center that are not minor images of one another (diastereomers). The term "chiral center" refers to a carbon atom to which four different groups are attached. The term "enantiomer" or "enantiomeric" refers to a molecule that is nonsuperimposeable on its minor image and hence optically active wherein the enantiomer π rotates the plane of polarized light in one direction and its minor image rotates the plane of polarized light in the opposite direction. The term "racemic" refers to a mixture of equal parts of enantiomers and which is optically inactive. The term "resolution" refers to the separation or concentration or depletion of one of the two enantiomeric forms of a molecule. The present invention is further directed to a method of decreasing the potential for abuse of an opioid agonist in an oral dosage form. The method comprises providing the opioid agonist in an oral dosage form as described herein. BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a graphical representation ofthe results of Example 20. Figure 2 is a graphical representation ofthe results of Example 23. Figure 3 is a graphical representation ofthe results of Example 24. DETAILED DESCRIPTION OF THE INVENTION It has been postulated that there exists at least three subspecies of opioid receptors, designated mu, kappa, and delta. Within this framework, the mu receptor is considered to be involved in the production of superspinal analgesia, respiratory depression, euphoria, and physical dependence. The kappa receptor is considered to be involved in inducing spinal analgesia, miosis and sedation. Activation ofthe gamma receptors causes dysphoria and hallucinations, as well as respiratory and vasomotor stimulatory effects. A receptor distinct from the mu receptor and designated gamma has been described in the mouse vas deferens, Lord, et al. Nature, 1977, 267, 495-99. Opioid agonists are thought to exert their agonist actions primarily at the mu receptor and to a lesser degree at the kappa receptor. There are a few drugs that appear to act as partial agonists at one receptor type or another. Such drugs exhibit a ceiling effect. Such drugs include naloφhine, propiram, and buprenoφhine. Still other drugs act as competitive antagonists at the mu receptor and block the effects of moφhine-like drugs, by exerting their actions at the kappa and omega receptors. The term i 8 agonist-antagonist has evolved to describe such mechanism of actions. The present invention is directed to a controlled release opioid analgesic, similar in analgesic spectrum to existing controlled-release opioid analgesics, which is formulated in order to reduce and minimize misuse, abuse and diversion. In certain embodiments, these characteristics are conferred by the inclusion of an opioid antagonist such as naltrexone HCl, which is itself formulated in a unique controlled release matrix. The properties of this formulation are developed to liberate the antagonist in conditions of misuse or tampering yet a negligible amount of antagonist would be released (an amount which does not affect the analgesia experienced by the patient) under the prescribed conditions of use. In certain embodiments ofthe invention, the release for the antagonist component of the formulation is expressed in terms of a ratio ofthe release achieved after tampering, e.g.. by crushing or chewing, relative to the amount released from the intact formulation. The ratio is therefore expressed as [Crushed] / [Whole], and it is desired that this ratio have a numerical range of at least 4:1 or greater (crushed release in 1 hour/ intact release in 1 hour). When the antagonist is naltrexone, it is preferable that the intact dosage fonri releases less than 0.25 mg, preferably 0.125 mg or less within 1 hour, with 0.25mg or greater naltrexone released after 1 hour when the dosage form is crushed or chewed. The derivation of these values are described in Example 17, 18 and 19. The present invention provides an oral dosage form of opioid agonist useful for decreasing the potential for abuse ofthe opioid agonist contained therein. The present invention includes an oral dosage form comprising an orally therapeutically effective amount of an opioid agonist in combination with an opioid antagonist. The opioid antagonist is present in a substantially non-releasable form. In certain preferred embodiments, the opioid antagonist in a substantially non- releasable form comprises opioid antagonist particles coated with a coating that substantially prevents its release. In preferred embodiments, such coating surrounds the antagonist particles and is impermeable to the drug and is insoluble in the gastrointestinal system. When the dosage form of the present invention is orally administered to humans, the opioid antagonist is not substantially released from the coating and is, therefore, not available for absoφtion into the body. Thus, the opioid antagonist, although present in the dosage form, does not substantially block the analgesic effectiveness ofthe opioid agonist. However, if the oral dosage form ofthe present invention is tampered with as to compromise the integrity of the coating, the opioid antagonist contained therein would be made available to at least partially block the effect of the opioid agonist. This characteristic decreases the potential for abuse or diversion ofthe opioid agonist in the oral dosage form. For example, if one attempts to abuse the drug contained in the oral dosage form of the present invention by, e.g., chewing. crushing, grinding or dissolving it in a solvent with heat (e.g., greater than about 45°C to about 50°C), the coating will be damaged and will no longer prevent the opioid antagonist from being released. Upon administration, the opioid antagonist will be released and significantly block the euphoric effect ofthe opioid agonist. In certain embodiments of the invention, the ratio of the opioid agonist to the coated opioid antagonist is such that when the oral dosage form is tampered with as to compromise the integrity ofthe coating that renders the opioid antagonist substantially non-releasable, the euphoric effect ofthe agonist would be negated by the opioid antagonist when misused by a human subject orally, parenterally, intranasally or sublingually. In certain prefened embodiments ofthe invention, the euphoric effect of the opioid agonist would be negated by the opioid antagonist when misused parenterally or sublingually. The present invention also includes an oral dosage form which comprises a releasable form of an opioid antagonist, along with an opioid agonist and coated opioid antagonist particles, the ratio of the agonist to the non-coated opioid antagonist being such, when administered orally as intended, the oral dosage form is analgesically effective. In certain other embodiments ofthe present invention, the opioid antagonist in a substantially non-releasable form comprises an opioid antagonist dispersed in a matrix that renders the antagonist substantially non-releasable, wherein the matrix comprises one or more of a pharmaceutically acceptable hydrophobic material. The antagonist is substantially not released from the matrix, thus is not made available to be absorbed during its transit through the gastrointestinal system. In certain other embodiments ofthe present invention, the opioid antagonist in a so matrix that renders the antagonist substantialh non-releasable comprises an opioid antagonist dispersed m a melt-extruded matnx, wherein the matrix comprises one or more of a pharmaceutically acceptable hydrophobic material In prefened embodiments, opioid agonists useful in the present invention include, but are not limited to, alfentaml, allylprodme, alphaprodme, amleπdine, benzylmoφhme, bezitramide, buprenoφhine, butoφhanol, clomtazene, codeine, desomoφhme, dextromoramide, dezocme, diampromide, diamoφhone, dihydrocodeme, dihydromoφhme, dimenoxadol, dimepheptanol, dimethylthiambutene, dioxaphetyl butyrate, dipipanone, eptazocme, ethoheptazine, ethylmethylthiambutene, efhylmoφhine, etomtazene, etoφhme, dihydroetoφhine, fentanyl and derivatives, herom, hydrocodone, hydromoφhone, hydroxypethid e, isomethadone, ketobemidone, levoφhanol, levophenacylmoφhan, lofentaml, mependme, meptazmol, metazocme, methadone, metopon, moφhme, myrophme, narceine, nicomoφhme, norlevoφhanol, normethadone, naloφhme, nalbuphene, normoφhme, noφipanone, opium, oxycodone, oxymoφhone, papaveretum, pentazocine, phenadoxone, phenomoφhan, phenazocme, phenopeπdme, pimmodme, piπtramide, propheptazine, promedol, propendme, propoxyphene, sufentaml, tihdme, tramadol, mixtures of any ofthe foregoing, salts of any ofthe foregoing, and the like In certain embodiments, the amount ofthe opioid agonist in the claimed opioid composition may be about 75 ng to 750 mg In certain prefened embodiments, the opioid agonist is selected from the group consisting of hydrocodone, moφhme, hydromoφhone, oxycodone, codeine, levoφhanol, mependme, methadone, oxymoφhone, buprenoφhine, fentanyl and derivatives thereof, dipipanone, herom, tramadol, etoφhme, dihydroetoφhine, butoφhanol, levoφhanol, or salts thereof or mixtures thereof In certain preferred embodrments, the opioid agonist is oxycodone or hydrocodone Equianalgesic doses of these opioids, m comparison to a 15 mg dose of hydrocodone, are set forth m Table 1 below 3 Table 1: Equianalgesic Doses of Opioids Although hydrocodone and oxycodone are effective in the management of pain, there has been an increase in their abuse by individuals who are psychologically dependent on opioids or who misuse opioids for non-therapeutic reasons. Previous experience with other opioids has demonstrated a decreased abuse potential when opioids are administered in combination with a narcotic antagonist especially in patients who are ex-addicts. W τ einhold LL, et al. Buprenoφhine Alone and in Combination with Naltrexone in Non-Dependent Humans, Drug and Alcohol Dependence 1992; 30:263-274; Mendelson J., et al., Buprenoφhine and Naloxone Interactions in Opiate-Dependent Volunteers, Clin Pharm Tlier. 1996; 60:105-114; both of which are hereby incoφorated by reference. These combinations, however, do not contain the opioid antagonist that is in a substantially non-releasable form. Rather, the opioid antagonist is released in the gastrointestinal system when orally administered and is made available for absoφtion, relying on the physiology ofthe host to differentially metabolize the agonist and antagonist and negate the agonist effects. Hydrocodone is a semisynthetic narcotic analgesic and antitussive with multiple central nervous system and gastrointestinal actions. Chemically, hydrocodone is 4,5-epoxy- 3-methoxy-17-methylmoφhinan-6-one, and is also known as dihydrocodeinone. Like other opioids, hydrocodone may be habit forming and may produce drug dependence ofthe 30- morphine type In excess doses hydrocodone, like other opium derivatives, w ill depiess respiration Oral hydrocodone is also available in Europe (Belgium, Germany, Greece, Italy, Luxembourg, Norway and Switzerland) as an antitussive agent A parenteral formulation is also available in Germany as an antitussive agent For use as an analgesic, hydrocodone bitartrate is commercially available in the United States only as a fixed combination with non-opiate drugs (l e , ibuprofen, acetaminophen, aspirin, etc ) for relief of moderate or moderately severe pam A common dosage form of hydrocodone is in combination with acetaminophen and is commercially available, e g , as Lortab® in the U S from UCB Pharma, Inc as 2 5/500 mg, 5/500 mg, 7 5/500 mg and 10/500 mg hydrocodone/acetammophen tablets Tablets aie also available m the ratio of 7 5mg hydrocodone bitartrate and 650mg acetaminophen, and 7 5mg hydrocodone bitartrate and 750mg acetaminophen Hydrocodone in combination with aspirin is given m an oral dosage form to adults generally in 1-2 tablets every 4-6 hours as needed to alleviate pain The tablet form is 5mg hydrocodone bitartrate and 224mg aspmn with 32mg caffeine, or 5mg hydrocodone bitartrate and 500mg aspinn A relatively new formulation comprises hydrocodone bitartrate and ibuprofen Vicoprofen®, commercially available in the U S from Knoll Laboratones, is a tablet containing 7 5 mg hydrocodone bitartrate and 200 mg ibuprofen The present invention is contemplated to encompass all such formulations, with the inclusion ofthe opioid antagonist particles coated with a coating that renders the antagonist substantially non-releasable Oxycodone, chemically known as 4,5-expoxy-14-hydroxy-3-methoxy-17- methylmoφhman-6-one, is an opioid agonist whose principal therapeutic action is analgesia Other therapeutic effects of oxycodone include anxiolysis, euphoria and feelings of relaxation The precise mechanism of its analgesic action is not known, but specific CNS opioid receptors for endogenous compounds with opioid-hke activity have been identified throughout the bram and spmal cord and play a role m the analgesrc effects of this drug Oxycodone is commercially available in the United States, e g , as Oxycontin ® from Purdue Pharma L P as controlled-release tab lleettss ffcor oral administration containing 10 mg, 20 3 mg, 40 mg or 80 mg oxycodone hydrochloride, and as OxylR™, also from Purdue Pharma L P , as immediate-release capsules containing 5 mg oxycodone hydrochloride The piesent invention is contemplated to encompass all such formulations, with the inclusion of an opioid antagonist m a substantially non-releasable form In preferred embodiments, the opioid antagonist of the present invention includes naltrexone, nalmefene, cyclazacme, levalloφhan and mixtures thereof In certain prefened embodiments, the opioid antagonist is naloxone or naltrexone In certain embodiments, the amount ofthe opioid antagonist, present m a substantially non-releasable form, may be about 10 ng to 275 mg Naloxone is an opioid antagonist which is almost void of agonist effects Subcutaneous doses of up to 12 mg of naloxone produce no discernable subjective effects, and 24 mg naloxone causes only slight drowsiness Small doses (0 4-0 8 mg) of naloxone given intramuscularly or intravenously in man prevent or promptly reverse the effects of moφhme-hke opioid agonist One mg of naloxone intravenously has been reported to completely block the effect of 25 mg of herom The effects of naloxone are seen almost immediately after intravenous administration The drug is absorbed after oral administration but has been reported to be metabolized into an inactive form rapidly in its fust passage through the liver such that it has been reported to have significantly lower potency than as when parenterally administered Oral dosage of more than lg have been reported to be almost completely metabolized in less than 24 hours It has been reported that 25% of naloxone administered sublingually is absorbed Wemberg, et al , Sublmgual Absoφtion of selected Opioid Analgesics, Clm Pharmacol Ther (1988), 44 335-340 Other opioid antagonists, for example, cyclazocme and naltrexone, both of which have cyclopropylmethyl substitutions on the nitrogen, retain much of their efficacy by the oral route and their durations of action are much longer, approaching 24 hours after oral doses In the treatment of patients previously addicted to opioids, naltrexone has been used in large oral doses (over 100 mg) to prevent euphorigemc effects of opioid agonists Naltrexone has been reported to exert strong preferential blocking action against mu over delta sites ai Naltrexone is known as a synthetic congener of oxymoφhone with no opioid agonist properties, and differs in structure from oxymoφhone by the replacement of the methyl group located on the nitrogen atom of oxymoφhone with a cyclopropylmefhyl group. The hydrochloride salt of naltrexone is soluble in water up to about 100 mg/cc. The pharmacological and pharmacokinetic properties of naltrexone have been evaluated in multiple animal and clinical studies. See, e.g., Gonzalez JP, et al. Naltrexone: A review of its Pharmacodynamic and Pharmacokinetic Properties and Therapeutic Efficacy in the Management of Opioid Dependence. Drugs 1988; 35:192-213, hereby incoφorated by reference. Following oral administration, naltrexone is rapidly absorbed (within 1 hour) and has an oral bioavailability ranging from 5-40%. Naltrexone's protein binding is approximately 21%) and the volume of distribution following single-dose administration is 16.1 L/kg. Naltrexone is commercially available in tablet form (Revia , DuPont) for the treatment of alcohol dependence and for the blockade of exogenously administered opioids. See, e.g., Revia (naltrexone hydrochloride tablets). Physician Desk Reference 51 st ed., Montvale, NJ. "Medical Economics" 1997; 51 :957-959. A dosage of 50 mg Revia ® blocks the pharmacological effects of 25 mg IV administered heroin for up to 24 hours. It is known that when co administered with moφhine, heroin or other opioids on a chronic basis, naltrexone blocks the development of physical dependence to opioids. It is believed that the method by which naltrexone blocks the effects of heroin is by competitively binding at the opioid receptors. Naltrexone has been used to treat narcotic addiction by complete blockade ofthe effects of opioids. It has been found that the most successful use of naltrexone for a narcotic addiction is with narcotic addicts having good prognosis, as part of a comprehensive occupational or rehabilitative program involving behavioral control or other compliance enhancing methods. For treatment of narcotic dependence with naltrexone, it is desirable that the patient be opioid- free for at least 7-10 days. The initial dosage of naltrexone for such puφoses has typically been about 25 mg, and if no withdrawal signs occur, the dosage may be increased to 50 mg per day. A daily dosage of 50 mg is considered to produce adequate clinical blockade ofthe actions of parenterally administered opioids. Naltrexone has also been used for the treatment of alcoholism as an adjunct with social and psychotherapeutic methods. 5 ~ In certain embodiments ofthe present invention, ratio of the opioid agonist to the substantially non-releasable form of an opioid antagonist in the oral dosage fonri is such that the effect ofthe opioid agonist is at least partially blocked when the dosage form is chewed, crushed or dissolved in a solvent and heated, and administered orally, intranasally, parenterally or sublingually. Since the oral dosage form ofthe present invention, when administered properly as intended, would not substantially release the opioid antagonist, the amount of such antagonist may be varied more widely than if the opioid antagonist is available to be released into the gastrointestinal system upon oral administration. For safety reasons, the amount ofthe antagonist present in a substantially non-releasable fonri should not be harmful to humans even if fully released. The ratio of particular opioid agonist to antagonist can be determined without undue experimentation by one skilled in the art. In certain embodiments ofthe present invention, the ratio of the opioid agonist and the opioid antagonist, present in a substantially non-releasable form, is about 1 :1 to about 50:1 by weight, preferably about 1 : 1 to about 20: 1 by weight. In certain preferred embodiments, the ratio is about 1:1 to about 10:1 by weight. In a preferred embodiment of the invention, the opioid agonist comprises oxycodone or hydrocodone and is present in the amount of about 15-45 mg and the opioid antagonist comprises naltrexone and is present in about 0.5-5 mg. The oral dosage form ofthe present invention may further include, in addition to an opioid agonist and antagonist, one or more drugs that may or may not act synergistically therewith. Thus, in certain embodiments, a combination of two opioid agonists may be included in the dosage form, in addition to the opioid antagonist. For example, the dosage form may include two opioid agonists having different properties, such as half-life, solubility, potency, and a combination of any ofthe foregoing. In yet further embodiments, one or more opioid agonist is included and a further non-opioid drug is also included, in addition to the opioid antagonist. Such non-opioid drugs would preferably provide additional analgesia, and include, for example, aspirin, acetaminophen; non-steroidal anti-inflammatory drugs ("NSAIDS"), e.g., ibuprofen, ketoprofen, etc.; N-methyl-D-aspartate (NMD A) receptor antagonists, e.g., a moφhinan such as dextromethoφhan or dextroφhan, or ketamine; cycooxygenase-II inhibitors ("COX-II inhibitors"); and/or glycine receptor antagonists. % In certain prefened embodiments ofthe present invention, the invention allows for the use of lower doses of the opioid analgesic by virtue ofthe inclusion of an additional non- opioid agonist, such as an NSAID or a COX-2 inhibitor. By using lower amounts of either or both drugs, the side effects associated with effective pain management in humans are reduced. Suitable non-steroidal anti-inflammatory agents, including ibuprofen, diclofenac, naproxen, benoxaprofen, flurbiprofen, fenoprofen, flubufen, ketoprofen, indoprofen, piroprofen, caφrofen, 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, fiufenisal. piroxicam, sudoxicam or isoxicam, and the like. Useful dosages of these drugs are well known to those skilled in the art. N-methyl-D-aspartate (NMD A) receptor antagonists are well known in the art, and encompass, for example, moφhinans such as dextromethoφhan or dextroφhan, ketamme, d- methadone or pharmaceutically acceptable salts thereof. For puφoses of the present invention, the term "NMDA antagonist" is also deemed to encompass drugs that block a major intracellular consequence of NMDA-receptor activation, e.g. a ganglioside such as GM, or GT, b a phenothiazine such as trifluoperazine or a naphthalenesulfonamide such as N- (6-aminothexyl)-5-chloro-l -naphthalenesulfonamide. These drugs are stated to inhibit the development of tolerance to and/or dependence on addictive drugs, e.g., narcotic analgesics such as moφhine, codeine, etc. in U.S. Pat. Nos. 5,321,012 and 5,556,838 (both to Mayer, et al.), and to treat chronic pain in U.S. Pat. No. 5,502,058 (Mayer, et al.), all of which are hereby incoφorated by reference. The NMDA antagonist may be included alone, or in combination with a local anesthetic such as lidocaine, as described in these Mayer, et. al. patents. The treatment of chronic pain via the use of glycine receptor antagonists and the identification of such drugs is described in U.S. Pat. No. 5,514,680 (Weber, et al.), hereby incoφorated by reference. 21 COX-2 inhibitors have been reported m the art and many chemical structures are known to produce inhibition of cyclooxygenase-2 COX-2 inhibitors are described, for example, in U S Patent Nos 5,616,601, 5,604,260, 5,593,994, 5,550,142, 5,536,752, 5,521,213, 5,475,995, 5,639,780, 5,604,253, 5,552,422, 5,510,368, 5,436,265, 5,409,944, and 5,130,311, all of which are hereby incoφorated by reference Certain prefened COX-2 inhibitors include celecoxib (SC-58635), DUP-697, flosuhde (CGP-28238), meloxicam, 6- methoxy-2 naphthylacetic acid (6-MNA), MK-966 (also known as Vioxx), nabumetone (prodrug for 6-MNA), mmesuhde, NS-398, SC-5766, SC-58215, T-614, or combinations thereof Dosage levels of COX-2 inhibitor on the order of from about 0 005 mg to about 140 mg per kilogram of body weight per day are therapeutically effective m combination with an opioid analgesic Alternatively, about 0 25 mg to about 7 g per patient per day of a COX-2 inhibitor is administered in combination with an opioid analgesic In yet further embodiments, a non-opioid drug can be included which provides a desired effect other than analgesia, e g , antitussive, expectorant, decongestant, antihistamme drugs, local anesthetics, and the like PREPARATION OF OPIOID ANTAGONIST IN A SUBSTANTIALLY NON-RELEASABLE FORM: In certain embodiments ofthe present m\ ention, an opioid antagonist m a substantially non-releasable form may be prepared by combining the antagonist with one oi more of a pharmaceutically acceptable hydrophobic material Foi example, opioid antagonist particles may be coated with coating that substantially prevents the release of the antagonist, the coating compnsing the hydrophobic mateπals(s) Another example would be an opioid antagonist that is dispersed m a matnx that renders the antagonist to be substantially non- releasable, the matnx compnsing the hydrophobic mateπals(s) In certain embodiments, the pharmaceutical acceptable hydrophobic matenal comprises a cellulose polymer selected from the group consisting of ethylcellulose, cellulose acetate, cellulose propionate (lower, medium or higher molecular weight), cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate and cellulose triacetate An example of ethylcellulose is one that has an ethoxy content of 44 to 55% Ethylcellulose may be used m the form of an alcoholic solution In certain other embodiments, the hydrophobic material comprises polylactic acid, polyglycohc acid or a co-polymer ofthe polylactic and polyglycohc acid 26 In certain embodiments, the hydrophobic material may comprise a cellulose polymer selected from the group consisting of cellulose ether, cellulose ester, cellulose ester ether, and cellulose. The cellulosic polymers have a degree of substitution, D.S., on the anhydroglucose unit, from greater than zero and up to 3 inclusive. By degree of substitution is meant the average number of hydroxyl groups present on the anhydroglucose unit comprising the cellulose polymer that are replaced by a substituting group. Representative materials include a polymer selected from the group consisting of cellulose acylate, cellulose diacylate, cellulose triacylate, cellulose acetate, cellulose diacetate, cellulose triacetate, mono, di, and tricellulose alkanylates, moni, di, and tricellulose aroylates, and mono, di, and tricellulose alkenylates. Exemplary polymers include cellulose acetate having a D.S. and an acetyl content up to 21%; cellulose acetate having an acetyl content up to 32 to 39.8%; cellulose acetate having a D.S. of 1 to 2 and an acetyl content of 21 to 35%>; cellulose acetate having a D.S. of 2 to 3 and an acetyl content of 35 to 44.8%. More specific cellulosic polymers include cellulose propionate having a D.S. of 1.8 and a propyl content of 39.2 to 45 and a hydroxyl content of 2.8 to 5.4%; cellulose acetate butyrate having a D.S. of 1.8, an acetyl content of 13 to 15% and a butyryl content of 34 to 39%; cellulose acetate butyrate having an acetyl content of 2 to 29%, a butyryl content of 17 to 53%o and a hydroxyl content of 0.5 to 4.7%; cellulose triacylate having a D.S. of 2.9 to 3 such as cellulose triacetate, cellulose trivalerate, cellulose trilaurate, cellulose tripatmitate, cellulose trisuccinate, and cellulose trioctanoate; cellulose diacylates having a D.S. of 2.2 to 2.6 such as cellulose disuccinate, cellulose dipalmitate, cellulose dioctanoate, cellulose dipentanoate, and coesters of cellulose such as cellulose acetate butyrate, cellulose acetate octanoate butyrate and cellulose acetate propionate. Additional cellulose polymers useful for preparing an opioid antagonist in a substantially non-releasable form includes acetaldehyde dimethyl cellulose acetate, cellulose acetate ethylcarbamate, cellulose acetate methylcarbamate, and cellulose acetate dimethylaminocellulose acetate. An acrylic polymer useful for preparation of the opioid antagonist in a substantially non-releasable form includes, but are not limited to, acrylic resins comprising copolymers 3< synthesized from acrylic and methacrylic acid esters (e.g., the copolymer of acrylic acid lower alkyl ester and methacrylic acid lower alkyl ester) containing about 0.02 to 0.03 mole of a tri (lower alkyl) ammonium group per mole of the acrylic and methacrylic monomers used. An example of a suitable acrylic resin is a polymer manufactured by Rohm Pharma GmbH and sold under the Eudragit RS trademark. Eudragit RS30D is prefened. Eudragit RS is a water insoluble copolymer of ethyl acrylate (EA), methyl methacrylate (MM) and trimethylammoniumethyl methacrylate chloride (TAM) in which the molar ratio of TAM to the remaining components (EA and MM) is 1 :40. Acrylic resins such as Eudragit RS may be used in the form of an aqueous suspension. In certain embodiments ofthe invention, the acrylic polymer may be selected from the group consisting of acrylic acid and methacrylic acid copolymers, methyl methacrylate copolymers, ethoxyethyl methacrylates, cyanoethyl methacrylate, poly(acrylic acid), poly(methacrylic acid), methacrylic acid alkylamide copolymer, poly(methyl methacrylate), polymethacrylate, poly(mefhyl methacrylate) copolymer, polyacrylamide, aminoalkyl methacrylate copolymer, poly(methacrylic acid anhydride), and glycidyl methacrylate copolymers. When the opioid antagonist in a substantially non-releasable form comprises opioid antagonist particles coated with a coating that renders the antagonist substantially non- releasable, and when a cellulose polymer or an acrylic polymer is used for preparation ofthe coating composition, suitable plasticizers, e.g., acetyl triethyl citrate and/or acetyl tributyl citrate may also be admixed with the polymer. The coating may also contain additives such as coloring agents, talc and/or magnesium stearate, which are well known in the coating art. The coating composition may be applied onto the opioid antagonist particles by spraying it onto the particles using any suitable spray equipment known in the part. For example, a Wuster fluidized-bed system may be used in which an air jet, injected from underneath, fluidizes the coated material and effects drying while the insoluble polymer coating is sprayed on. The thickness ofthe coating will depend on the characteristics of the particular coating composition being used. However, it is well within the ability of one skilled in the art to determine by routine experimentation the optimum thickness of a particular coating required for a particular dosage form ofthe present invention. 3) The pharmaceutically acceptable hydrophobic material useful for preparing an opioid antagonist in a substantially non-releasable form includes a biodegradable polymer comprising a poly(lactic /glycolic acid) ("PLGA"), a polylactide, a polyglycolide, a polyanhydride, a polyorthoester, polycaprolactones, polyphosphazenes, polysaccharides, proteinaceous polymers, polyesthers, polydioxanone, polygluconate, polylactic-acid- polyethylene oxide copolymers, poly(hydroxybutyrate), polyphosphoesther or mixtures or blends of any of these. In certain embodiments, biodegradable polymer comprises a poly(lactic/glycolic acid), a copolymer of lactic and glycolic acid, having molecular weight of about 2,000 to about 500,000 daltons. The ratio of lactic acid to glycolic acid is from about 100:0 to about 25:75, with the ratio of lactic acid to glycolic acid of 65:35 being preferred. Poly(lactic/glycolic acid) may be prepared by the procedure set forth in U.S. Patent No. 4,293,539 (Ludwig et al.), the disclosure of which is hereby incoφorated by reference in its entirety. In brief, Ludwig prepares the copolymer by condensation of lactic acid and glycolic acid in the presence of a readily removable polymerization catalyst (e.g., a strong acid ion-exchange resin such as Dowex HCR-W2-H). The amount of catalyst is not critical to the polymerization, but typically is from about 0.01 to about 20 parts by weight relative to the total weight of combined lactic acid and glycolic acid. The polymerization reaction may be conducted without solvents at a temperature from about 100 C to about 250 C for about 48 to about 96 hours, preferably under a reduced pressure to facilitate removal of water and byproducts. Poly(lactic/glycolic acid) is then recovered by filtering the molten reaction mixture in an organic solvent such as dichloromethane or acetone and then filtering to remove the catalyst. Once the opioid antagonist in a substantially non-releasable form is prepared, it may be combined with an opioid agonist, along with conventional excipients known in the art, to prepare the oral dosage form ofthe present invention. In certain preferred embodiments ofthe invention, the oral dosage form is a capsule or a tablet. When being formulated as a tablet, the opioid antagonist and agonist may be combined with one or more inert, non-toxic phanriaceutical excipients which are suitable foi the manufacture of tablets Such excipients include, for example, an inert diluent such as lactose, granulating and disintegrating agents such as cornstarch, binding agents such as starch, and lubncatmg agents such as magnesium stearate The oral dosage form of the present invention may be formulated to provide immediate release ofthe opioid agonist contained therein In other embodiments of the invention, however, the oral dosage form provides sustained-release of the opioid agonist In certain embodiments, the oral dosage forms providing sustained release ofthe opioid agonist may be prepared by admixing the opioid antagonist in a substantially non- releasable form with the agonist and desirable pharmaceutical excipients to provide a tablet, and then coating the tablet with a sustained-release tablet coating In certain embodiments of the invention, sustained release opioid agonist tablets may be prepared by admixing the substantially non-releasable form of an opioid antagonist with an opioid antagonist in a matnx that provides the tablets with sustained-releasing properties Detailed description for preparmg sustained-release oral dosage forms according to the present invention is set forth below PREPARATION OF CONTROLLED RELEASE DOSAGE FORMS CONTAINING AN OPIOID AGONIST AND A SUBSTANTIALLY ON-RELEASABLE FORM OF AN OPIOID ANTAGONIST A combination ofthe opioid agonist and a substantially non-releasable form of an opioid antagonist may be formulated as a controlled or sustained release oral formulation in any suitable tablet, coated tablet or multiparticulate formulation known to those skilled m the art The sustained release dosage form may optionally include a sustained release earner which is incoφorated into a matrix along w ith the opioid agonist and a non-available fonri of an opioid antagonist, or may be applied as a sustained release coating In embodiments in which the opioid agonist comprises hydrocodone, the sustained release oral dosage forms may include analgesic doses from about 8 mg to about 50 mg of hydrocodone per dosage unit In sustained release oral dosage forms where hydromoφhone 3 is the therapeutically active opioid. it is included in an amount from about 2 mg to about 64 mg hydromoφhone hydrochloride. In another embodiment, the opioid agonist comprises moφhine, and the sustained release oral dosage forms ofthe present invention include from about 2.5 mg to about 800 mg moφhine, by weight. In yet another embodiment, the opioid agonist comprises oxycodone and the sustained release oral dosage forms include from about 2.5 mg to about 800 mg oxycodone. In certain prefened embodiments, the sustained release oral dosage forms include from about 20 mg to about 30 mg oxycodone. Controlled release oxycodone formulations are known in the art. The following documents describe various controlled release oxycodone formulations suitable for use in the invention described herein, and processes for their manufacture: U.S. Patent Nos. 5,266,331; 5,549,912; 5,508,042; and 5,656,295. The opioid agonist may comprise tramadol and the sustained release oral dosage forms may include from about 25 mg to 800 mg tramadol per dosage unit. The dosage fonn may contain more than one opioid agonist to provide a substantially equivalent therapeutic effect. Alternatively, the dosage form may contain molar equivalent amounts of other salts of the opioid agonists useful in the present invention. In one prefened embodiment ofthe present invention, the sustained release dosage form comprises such particles comprising the opioid agonist, wherein the particles have diameter from about 0.1 mm to about 2.5 mm, preferably from about 0.5 mm to about 2 mm. The opioid agonist particles are preferably film coated with a material that permits release ofthe opioid agonist at a sustained rate in an aqueous medium. The film coat is chosen so as to achieve, in combination with the other stated properties, a desired in-vitro release rate. The sustained release coating formulations ofthe present mvention should be capable of producing a strong, continuous film that is smooth and elegant, capable of supporting pigments and other coating additives, non-toxic, inert, and tack-free. The dosage forms comprising an opioid agonist and a substantially non-releasable opioid antagonist may optionally be coated with one or more materials suitable for the regulation ofthe opioid agonist release or for the protection ofthe formulation. In one embodiment, coatings are provided to permit either pH-dependent or pH-independent release, e.g., when exposed to gastrointestinal fluid. A pH-dependent coating serves to release the opioid in desired areas ofthe gastro-intestinal (GI) tract, e.g., the stomach or small intestine, such that an absoφtion profile is provided which is capable of providing at least about eight hours and preferably about twelve hours to up to about twenty- four hours of analgesia to a patient. When a pH-independent coating is desired, the coating is designed to achieve optimal release ofthe opioid regardless of pH-changes in the environmental fluid, e.g., the Gl tract. It is also possible to formulate compositions which release a portion ofthe dose in one desired area of the GI tract, e.g., the stomach, and release the remainder ofthe dose in another area ofthe GI tract, e.g., the small intestine. Formulations according to the invention that utilize pH-dependent coatings to obtain formulations may also impart a repeat-action effect whereby unprotected drug is coated over the enteric coat and is released in the stomach, while the remainder, being protected by the enteric coating, is released further down the gastrointestinal tract. Coatings which are pH- dependent may be used in accordance with the present invention include shellac, cellulose acetate phthalate (CAP), polyvinyl acetate phthalate (PVAP), hydroxypropylmethylcellulose phthalate, and methacrylic acid ester copolymers, zein, and the like. In certain preferred embodiments, the substrate (e.g., tablet core bead, matrix particle) containing the opioid analgesic (with or without the COX-2 inhibitor) is coated with a hydrophobic material selected from (i) an alkylcellulose; (ii) an acrylic polymer; or (iii) mixtures thereof. The coating may be applied in the form of an organic or aqueous solution or dispersion. The coating may be applied to obtain a weight gain from about 2 to about 25 % ofthe substrate in order to obtain a desired sustained release profile. Coatings derived from aqueous dispersions are described, e.g., in detail in U.S. Patent Nos. 5,273,760 and 5,286,493, assigned to the Assignee ofthe present invention and hereby incoφorated by reference. Other examples of sustained release formulations and coatings which may be used in accordance with the present invention include Assignee's U.S. Patent Nos. 5,324,351 ; 5,356,467, and 5,472,712, hereby incoφorated by reference in their entirety. Alkylcellulose Polymers Cellulosic materials and polymers, including alkylcelluloses, provide hydrophobic materials well suited for coating the beads according to the invention Simply by way of example, one preferred alkylcellulosic polymer is ethylcellulose, although the artisan will appreciate that other cellulose and/or alkylcellulose polymers may be readily employed, singly or m any combination, as all or part of a hydrophobic coating according to the invention One commercially- available aqueous dispersion of ethylcellulose is Aquacoat (FMC Coφ , Philadelphia, Pennsylvania, U S A ) Aquacoat is prepared by dissolving the ethylcellulose in a water-immiscible organic soh ent and then emulsifying the same in water in the presence of a surfactant and a stabilizer After homogemzation to generate submicron droplets, the organic solvent is evaporated under \ acuum to fonri a pseudolatex The plasticizer is not incoφorated m the pseudolatex dunng the manufacturing phase Thus, pnoi to using the same as a coating, it is necessary to intimately mix the Aquacoat with a suitable plasticizer pnor to use Another aqueous dispersion of ethylcellulose is commercially available as Surelease (Colorcon, Inc , West Point, Pennsylvania, U S A ) This product is prepared by mcoφorating plasticizer into the dispersion dunng the manufacturing process A hot melt of a polymer, plasticizer (dibutyl sebacate), and stabilizer (oleic acid) is prepared as a homogeneous mixture, which is then diluted with an alkaline solution to obtain an aqueous dispersion which can be applied directly onto substrates Acrylic Polymers In other prefened embodiments ofthe present mvention, the hydrophobic material comprising the controlled release coating is a pharmaceutically acceptable acrylic polvmer including but not lrmited to acrylic acid and methacrylic acid copolymers, methyl methacrylate copolymers, ethoxyethyl methacrylates, cyanoethyl methacrylate, poly(acryhc acid), poly(methacryhc acid), methacrylic acid alkylamide copolymer, poly(methyl methacrylate), polymethacrylate, poly(methyl methacrylate) copolymer, polyacrylamide, aminoalkyl methacrylate copolymer, poly(mefhacrylic acid anhydride), and glycidyl methacrylate copolymers. In certain preferred embodiments, the acrylic polymer is comprised of one or more ammonio methacrylate copolymers. Ammonio methacrylate copolymers are well known in the art, and are described in NF XVII as fully polymerized copolymers of acrylic and methacrylic acid esters with a low content of quaternary ammonium groups. In order to obtain a desirable dissolution profile, it may be necessary to incoφorate two or more ammonio methacrylate copolymers having differing physical properties, such as different molar ratios of the quaternary ammonium groups to the neutral (mefh)acrylic esters. Certain methacrylic acid ester-type polymers are useful for preparing pH-dependent coatings which may be used in accordance with the present invention. For example, there are a family of copolymers synthesized from diethylaminoethyl methacrylate and other neutral methacrylic esters, also known as methacrylic acid copolymer or polymeric methacrylates, commercially available as Eudragit " from Rohm Tech, Inc. There are several different types of Eudragit . For example, Eudragit " E is an example of a methacrylic acid copolymer which swells and dissolves in acidic media. Eudragit L is a methacrylic acid copolymer which does not swell at about pH < 5.7 and is soluble at about pH > 6. Eudragit S does not swell at about pH < 6.5 and is soluble at about pH > 7. Eudragit " RL and Eudragit RS are water swellable, and the amount of water absorbed by these polymers is pH-dependent, however, dosage forms coated with Eudragit ® RL and RS are pH-independent. In certain preferred embodiments, the acrylic coating comprises a mixture of two acrylic resin lacquers commercially available from Rohm Pharma under the Tradenames Eudragit RL30D and Eudragit RS30D, respectively. Eudragit RL30D and Eudragit RS30D are copolymers of acrylic and methacrylic esters with a low content of quaternary ammonium groups, the molar ratio of ammonium groups to the remaining neutral (meth)acrylic esters being 1 :20 in Eudragit RL30D and 1 :40 in Eudragit " RS30D. The mean molecular weight is about 150,000. The code designations RL (high permeability) and RS (low permeability) refer to the permeability properties of these agents. Eudragit " RL/RS mixtures are insoluble in water and m digestive fluids However, coatings formed from the same are swellable and permeable m aqueous solutions and digestive fluids The Eudragit " RL/RS dispersions of the present invention may be mixed together in any desired ratio in order to ultimately obtain a sustained release formulatron having a desirable dissolution profile Desirable sustained release formulations may be obtained, for instance, from a retardant coating derived from 100% Eudragit RL, 50%o Eudragit RL and 50% Eudragit 8 RS, and 10% Eudragit ® RL Eudragit ® 90% RS Of course, one skilled in the art will recognize that other aery he polymers may also be used, such as, foi example, Eudragit " L Plasticizers In embodiments ofthe present mvention where the coating compnses an aqueous dispersion of a hydrophobic matenal, the inclusion of an effective amount of a plasticizer in the aqueous dispersion of hydrophobic material will further improve the physical properties ofthe sustained release coating For example, because ethylcellulose has a relatively high glass transition temperature and does not form flexrble films under normal coating conditions, it is preferable to incoφorate a plasticizer into an ethylcellulose coating containing sustained release coating before using the same as a coating material Generally, the amount of plasticizer included in a coating solution is based on the concentration of the film-former, e g , most often from about 1 to about 50 percent by weight of the film-former Concentration of the plasticizer. however, can only be propeily determined after careful experimentation with the particular coating solution and method of application Examples of suitable plasticizers for ethylcellulose include water insoluble plasticizers such as dibutyl sebacate, diethyl phthalate, tnethyl citrate, tπbutyl citrate, and tnacetm, although it is possible that other water-insoluble plasticizers (such as acetylated monoglycendes, phthalate esters, castor oil, etc ) may be used Tnethyl citrate is an especially prefened plastrcizer for the aqueous drspersions of ethyl cellulose of the present mvention Examples of suitable plasticizers for the acrylic polymers ofthe present invention include, but are not limited to citric acid esters such as tnethyl citrate NF XVI, tnbutyl citrate, dibutyl phthalate, and possibly 1,2-propylene glycol Other plasticizers which have pioved to be suitable for enhancing the elasticity ofthe films formed from acrylic films such as Eudragit RL/RS lacquer solutions include polyethylene glycols, propylene glycol, diethyl phthalate, castor oil, and tnacetm Tnethyl citrate is an especially prefened plasticizer for the aqueous dispersions of ethyl cellulose of the present invention It has further been found that the addition of a small amount of talc reduces the tendency ofthe aqueous dispersion to stick during processing, and acts as a polishing agent PROCESSES FOR PREPARING COATED BEADS When a hydrophobic controlled release coating material is used to coat inert pharmaceutical beads such as nu panel 18/20 beads, which are already coated with an opioid agonist, a plurality of the resultant solid controlled release beads may thereafter be placed in a gelatin capsule, with the opioid antagonist in a substantially non-releasable form The dosage form provides an effectrve controlled release dose ofthe opioid agonist when ingested and contacted by an environmental fluid, e.g , gastric fluid or dissolution media The controlled release bead formulations ofthe present invention slowly release the opioid agonist, e g , w hen ingested and exposed to gastric fluids, and then to intestinal fluids The controlled release profile ofthe formulations ofthe inv ention can be altered, foi example, by varying the amount of overcoating with the hydrophobic material, altering the manner in which the plasticizer is added to the hydrophobic material, by varying the amount of plasticizer relative to hydrophobic material, by the inclusion of additional ingredients oi excipients, by altering the method of manufacture, etc The dissolution profile ofthe ultimate product may also be modified, for example, by increasing or decreasing the thickness ofthe retardant coating Spheroids or beads coated with an opioid agonist may be prepared, e g , by dissolving the drug in water and then spraying the solution onto a substrate, for example, nu panel 18/20 beads, using a Wuster insert Optionally, additional ingredients are also added prior to 3β coating the beads in order to assist the binding ofthe opioid to the beads, and/or to color the solution, etc For example, a product which includes hydroxypropylmethylcellulose, etc with or without colorant (e g , Opadry , commercrally available from Colorcon, Inc ) may be added to the solution and the solution mixed (e g , for about 1 hour) prior to application ot the same onto the beads The resultant coated substrate, m this example beads, may then be optionally overcoated with a barrier agent, to separate the therapeutically active agent from the hydrophobic controlled release coating An example of a suitable barrier agent is one which compnses hydroxypropylmethylcellulose However, any film-former known in the art may be used It is prefened that the barrier agent does not affect the dissolution rate ofthe final product The beads may then be overcoated with an aqueous dispersion of the hydrophobic matenal The aqueous dispersion of hydrophobic material preferably further includes an effective amount of plasticizer, e g tnethyl citrate Pre-formulated aqueous dispersions of ethylcellulose, such as Aquacoat " or Surelease , may be used If Surelease is used, it is not necessary to separately add a plasticizer Alternatively, pre-formulated aqueous drspersions of acrylic polymers such as Eudragit " can be used The coating solutions ofthe present invention preferably contain, in addition to the film-former, plasticizer, and solvent system (l e , water), a colorant to provide elegance and product distinction Color may be added to the solution ofthe therapeutically active agent instead, or in addition to the aqueous dispersion of hydrophobic material For example, coloi may be added to Aquacoat via the use of alcohol or propylene glycol based color dispersions, milled aluminum lakes and opacifϊers such as titanium dioxide by adding color with shear to water soluble polymer solution and then using low shear to the plasticized Aquacoat Alternatively, any suitable method of providing color to the formulations of the present invention may be used Suitable ingredients for providing color to the formulation when an aqueous dispersion of an acrylic polymer is used include titanium dioxide and color pigments, such as iron oxide pigments The mcoφoration of pigments, may, however, increase the retard effect ofthe coating Plasticized hydrophobic material may be applied onto the substrate comprising the therapeutically active agent by spraying using any suitable spray equipment known m the art 3^ In a prefened method, a Wurster flurdized-bed system is used in which an an jet, injected from underneath, fluidizes the core matenal and effects drying while the acrylic polymei coating is sprayed on A sufficient amount ofthe hydrophobic material to obtain a predetei- mmed controlled release of said therapeutically active agent when the coated substrate is exposed to aqueous solutions, e g gastnc fluid, is preferably applied, taking into account the physical characteristics ofthe therapeutically active agent, the mannei of incoφoration of tht plasticizer, etc After coating w ith the hydrophobrc matenal, a further o\ eicoat of a film- former, such as Opadry , is optionally applied to the beads This overcoat is provided, if at all, in order to substantially reduce agglomeration ofthe beads The release of the therapeutically active agent from the controlled lelease fonnulation of the present invention can be further influenced, I e , adjusted to a desired rate, by the addition of one or more release-modifying agents, or by providing one oi more passageways through the coating The ratio of hydrophobic material to water soluble material is determined by, among other factors, the release rate required and the solubility characteristics ofthe matenals selected The release-modifying agents which function as pore-formers may be organic or inorganic, and include matenals that can be dissolved, extracted or leached from the coating in the environment of use The pore-formers may comprise one or more hydrophihc matenals such as hydroxypropylmethylcellulose The sustained release coatings ofthe present invention can also include erosion- promoting agents such as starch and gums The sustained release coatings ofthe present invention can also include materials useful for makmg microporous lamma in the environment of use, such as polycarbonates compnsed of linear polyesters of carbonic acid in which carbonate groups reoccur in the polymer chain The release-modifying agent may also comprise a semi-permeable polymer In certain prefened embodiments, the release-modifying agent is selected from hydroxypropylmethylcellulose, lactose, metal stearates, and mixtures of am of the foiegoing The sustained release coatings of the present invention may also include an exit means comprising at least one passage ay, orifice, or the like The passagew ay may be formed by such methods as those disclosed in U S Patent Nos 3,845,770, 3,916.889 4 063,064, and 4,088,864 (all of which are hereby incoφorated by reference) The passagew ay can ha\ e any shape such as round, triangular, square, elliptical, megular, etc MATRIX FORMULATIONS In other embodiments ofthe present invention, the controlled release fonn illation is achieved via a matrix having a controlled release coating as set forth abo\ e The piesent invention also comprises sustained-release tablets comprising an opioid agonist and opioid antagonist particles coated with a coating that renders the antagonist substantially non- releasable, wherein the agonist and the antagonist are dispersed in a controlled release matrix that affords m-vitro dissolution rates of the oproid agonist withm the prefened ranges and that releases the opioid agonist m a pH-dependent or pH-mdependent manner The materials suitable for inclusion in a controlled release matrix will depend on the method used to fonn the matnx For example, a matrix m addition to the opioid agonist and the substantially non releasable form ofthe coated opioid antagonist, may include Hydrophihc and/or hydrophobic materials, such as gums, cellulose etheis, aciyhc resins, protein denved matenals, the list is not meant to be exclusive, and any pharmaceutically acceptable hydrophobic material or hydrophihc material w hich is capable of imparting controlled release of the opioid may be used m accordance with the present invention Digestible, long chain (C 8 -C., 0 , especially C r -C 40 ), substituted or unsubstituted hydrocarbons, such as fatty acids, fatty alcohols, glyceryl esters of fatty acids, mmeial and vegetable oils and waxes, and stearyl alcohol, and polyalkylene glycols ^1 Of these polymers, acrylic polymers, especially Eudragit RSPO - the cellulose ethers, especially hydroxyalkylcelluloses and carboxyalkylcelluloses, are prefened. The oral dosage form may contain between 1% and 80% (by weight) of at least one hydrophihc or hydrophobic material. When the hydrophobic material is a hydrocarbon, the hydrocarbon preferably has a melting point of between 25 ° and 90°C. Ofthe long chain hydrocarbon materials, fatty (aliphatic) alcohols are prefened. The oral dosage form may contain up to 60% (by weight) of at least one digestible, long chain hydrocarbon. Preferably, the oral dosage form contains up to 60% (by weight) of at least one polyalkylene glycol. The hydrophobic material is preferably selected from the group consisting of alkylcelluloses, acrylic and methacrylic acid polymers and copolymers, shellac, zein, hydrogenated castor oil, hydrogenated vegetable oil, or mixtures thereof. In certain prefened embodiments ofthe present invention, the hydrophobic material is a pharmaceutically acceptable acrylic polymer, including but not limited to acrylic acid and methacrylic acid copolymers, methyl methacrylate, methyl methacrylate copolymers, ethoxyethyl methacrylates, cyanoethyl methacrylate, aminoalkyl methacrylate copolymer, poly(acrylic acid), poly(methacrylic acid), methacrylic acid alkylamine copolymer, poly(methyl methacrylate), poly(methacrylic acid)(anhydride), polymethacrylate, polyacrylamide, poly(methacrylic acid anhydride), and glycidyl methacrylate copolymers. In other embodiments, the hydrophobic material is selected from materials such as hydroxyalkylcelluloses such as hydroxypropylmethylcellulose and mixtures of the foregoing. Preferred hydrophobic materials are water-insoluble with more or less pronounced hydrophihc and/or hydrophobic trends. Preferably, the hydrophobic materials useful in the invention have a melting point from about 30° to about 200 °C, preferably from about 45 ° to about 90 °C. Specifically, the hydrophobic material may comprise natural or synthetic waxes, fatty alcohols (such as lauryl, myristyl, stearyl, cetyl or preferably cetostearyl alcohol), fatty acids, including but not limited to fatty acid esters, fatty acid glycerides (mono-, di-, and tri- glycerides), hydrogenated fats, hydrocarbons, normal waxes, stearic aid, stearyl alcohol and hydrophobic and hydrophihc materials having hydrocarbon backbones. Suitable waxes include, for example, beeswax, glycowax, castor wax and carnauba wax. For puφoses of the present invention, a wax-like substance is defined as any material which is normally solid at room temperature and has a melting point of from about 30° to about 100°C. Suitable hydrophobic materials which may be used in accordance with the present invention include digestible, long chain (C 8 -C 50 , especially C ]2 -C, 0 ), substituted or unsubstituted hydrocarbons, such as fatty acids, fatty alcohols, glyceryl esters of fatty acids. mineral and vegetable oils and natural and synthetic waxes. Hydrocarbons having a melting point of between 25° and 90°C are preferred. Of the long chain hydrocarbon materials, fatty (aliphatic) alcohols are prefened in certain embodiments. The oral dosage fonn may contain up to 60%) (by weight) of at least one digestible, long chain hydrocarbon. Preferably, a combination of two or more hydrophobic materials are included in the matrix formulations. If an additional hydrophobic material is included, it is preferably selected from natural and synthetic waxes, fatty acids, fatty alcohols, and mixtures ofthe same. Examples include beeswax, carnauba wax, stearic acid and stearyl alcohol. This list is not meant to be exclusive. One particular suitable matrix comprises at least one water soluble hydroxyalkyl cellulose, at least one C I2 -C 36 , preferably C i4 -C 22 , aliphatic alcohol and, optionally, at least one polyalkylene glycol. The at least one hydroxyalkyl cellulose is preferably a hydroxy (C to C 6 ) alkyl cellulose, such as hydroxypropylcellulose, hydroxypropylmethylcellulose and, especially, hydroxyethylcellulose. The amount of the at least one hydroxyalkyl cellulose in the present oral dosage form will be determined, inter alia, by the precise rate of opioid release required. The at least one aliphatic alcohol may be, for example, lauryl alcohol, myristyl alcohol or stearyl alcohol. In particularly preferred embodiments ofthe present oral dosage form, however, the at least one aliphatic alcohol is cetyl alcohol or cetostearyl alcohol. The amount ofthe at least one aliphatic alcohol in the present oral dosage form will be determined, as above, by the precise rate of opioid release required. It will also depend on whether at least one polyalkylene glycol is present in or absent from the oral dosage fonn. In the absence of at least one polyalkylene glycol, the oral dosage form preferably contains between 20% and 50% (by wt) of the at least one aliphatic alcohol. When at least one polyalkylene glycol is present in the oral dosage fonn, then the combined weight of the at least one aliphatic alcohol and the at least one polyalkylene glycol preferably constitutes between 20% and 50% (by wt) of the total dosage. In one embodiment, the ratio of, e.g., the at least one hydroxyalkyl cellulose or acrylic resin to the at least one aliphatic alcohol/ polyalkylene glycol determines, to a considerable extent, the release rate of the opioid from the formulation. A ratio of the at least one hydroxyalkyl cellulose to the at least one aliphatic alcohol/polyalkylene glycol of between 1 :2 and 1 :4 is prefened, with a ratio of between 1 :3 and 1 :4 being particularly prefened. The at least one polyalkylene glycol may be, for example, polypropylene glycol or, which is prefened, polyethylene glycol. The number average molecular weight of the at least one polyalkylene glycol is preferred between 1 ,000 and 15,000 especially between 1 ,500 and 12,000. Another suitable controlled release matrix would comprise an alkylcellulose (especially ethyl cellulose), a C 12 to C 36 aliphatic alcohol and, optionally, a polyalkylene glycol. In another prefened embodiment, the matrix includes a pharmaceutically acceptable combination of at least two hydrophobic materials. In addition to the above ingredients, a controlled release matrix may also contain suitable quantities of other materials, e.g. diluents, lubricants, binders, granulating aids, colorants, flavorants and glidants that are conventional in the pharmaceutical art. PROCESSES FOR PREPARING MATRIX - BASED BEADS In order to facilitate the preparation of a solid, controlled release, oral dosage fonn according to this invention, any method of preparing a matrix formulation known to those skilled in the art may be used. For example incoφoration in the matrix may be effected, for example, by (a) forming granules comprising at least one water soluble hydroxyalkyl cellulose and opioid or an opioid salt; (b) mixing the hydroxyalkyl cellulose containing granules with at least one C 12 - C. 6 aliphatic alcohol; and (c) optionally, compressing and shaping the granules. Preferably, the granules are formed by wet granulating the hydroxyalkyl cellulose/opioid with water. In a particularly prefened embodiment of this process, the amount of water added during the wet granulation step is preferably between 1.5 and 5 times, especially between 1.75 and 3.5 times, the dry weight of the opioid. In yet other alternative embodiments, a spheronizing agent, together with the active ingredient can be spheronized to fonn spheroids. Microcrystalline cellulose is preferred. A suitable microcrystalline cellulose is, for example, the material sold as Avicel PH 101 (Trade Mark, FMC Coφoration). In such embodiments, in addition to the active ingredient and spheronizing agent, the spheroids may also contain a binder. Suitable binders, such as low viscosity, water soluble polymers, will be well known to those skilled in the phannaceutical art. However, water soluble hydroxy lower alkyl cellulose, such as hydroxypropylcellulose, are prefened. Additionally (or alternatively) the spheroids may contain a water insoluble polymer, especially an acrylic polymer, an acrylic copolymer, such as a methacrylic acid-ethyl acrylate copolymer, or ethyl cellulose. In such embodiments, the sustained release coating will generally include a hydrophobic material such as (a) a wax, either alone or in admixture with a fatty alcohol; or (b) shellac or zein. Melt Extrusion Matrix Sustained release matrices can also be prepared via melt-granulation or melt-extrusion techniques, as long as the techniques used do not damage the integrity of the substantially non-releasable form ofthe opioid antagonist added during the preparation of the matrix to the extent that sufficient amount ofthe opioid antagonist becomes available to be released into the gastrointestinal system upon oral administration. Alternatively, the melt extrusion step may be performed with the opioid agonist to produce sustained release particles ofthe agonist, which may then be combined with the substantially non-releasable form ofthe opioid antagonist. Generally, melt-granulation techniques involve melting a normally solid hydrophobic material, e.g. a wax. and incoφorating a powdered drug therein. To obtain a sustained release dosage form, it may be necessary to incoφorate an additional hydrophobic substance, e.g. ethylcellulose or a water-insoluble acrylic polymer, into the molten wax hydrophobic material. Examples of sustained release formulations prepared via melt- granulation techniques are found in U.S. Patent No. 4,861,598, assigned to the Assignee of the present invention and hereby incoφorated by reference in its entirety. The additional hydrophobic material may comprise one or more water-insoluble waxlike thermoplastic substances possibly mixed with one or more wax-like thermoplastic substances being less hydrophobic than said one or more water-insoluble wax-like substances. In order to achieve constant release, the individual wax-like substances in the formulation should be substantially non-degradable and insoluble in gastrointestinal fluids during the initial release phases. Useful water-insoluble wax-like substances may be those with a water-solubility that is lower than about 1 :5,000 (w/w). In addition to the above ingredients, a sustained release matrix may also contain suitable quantities of other materials, e.g., diluents, lubricants, binders, granulating aids, colorants, flavorants and glidants that are conventional in the pharmaceutical art. The quantities of these additional materials will be sufficient to provide the desired effect to the desired formulation. In addition to the above ingredients, a sustained release matrix incoφorating melt- extruded multiparticulates may also contain suitable quantities of other materials, e.g. diluents, lubricants, binders, granulating aids, colorants, flavorants and glidants that are conventional in the pharmaceutical art in amounts up to about 50% by weight of the particulate if desired. Specific examples of pharmaceutically acceptable carriers and excipients that may be used to formulate oral dosage forms are described in the Handbook of Pharmaceutical Excipients, American Pharmaceutical Association (1986), incoφorated by reference herein. Melt Extrusion Multiparticulates The preparation of a suitable melt-extruded matrix according to the present invention may, for example, include the steps of blending the opioid analgesic, together with at least one hydrophobic material and preferably the additional hydrophobic material to obtain a homogeneous mixture The homogeneous mixture is then heated to a temperature sufficient to at least soften the mixture sufficiently to extrude the same The resulting homogeneous mixture is then extruded to form strands The extrudate is prefeiably cooled and cut into multiparticulates by any means known m the art The strands are cooled and cut into multiparticulates The multiparticulates are then blended with the opioid antagonist particles coated with a coating that renders the antagonist substantially non-releasable and dι\ ided into unit doses The extrudate preferably has a diameter of from about 0 1 to about 5 mm and provides sustained release ofthe opioid agonist for a time period of from about 8 to about 24 hours An optional process for prepanng the melt extrusions ofthe present invention include;, directly metering into an extruder a hydrophobic matenal, a therapeutically active agent, and an optional binder, heating the homogenous mixture, extruding the homogenous mixture to thereby form strands, cooling the strands containing the homogeneous mixture, cutting the strands into particles having a size from about 0 1 mm to about 12 mm, and combining the particles with the coated opioid antagonist particles and dividing them into unit doses In this aspect of the invention, a relatively continuous manufacturmg procedure is realized The diameter ofthe extruder aperture or exit port can also be adjusted to vary the thickness ofthe extruded strands Furthermore, the exit part ofthe extruder need not be round, it can be oblong, rectangular, etc The exiting strands can be reduced to particles using a hot wire cutter, guillotine, etc The melt extruded multiparticulate system can be, for example, in the form of granules, spheroids or pellets depending upon the extruder exit onfice For puφoses ofthe present mvention, the terms "melt-extruded multrpartιculate(s)" and "melt-extruded multiparticulate system(s)" and "melt-extruded particles" shall refer to a plurality of units, preferably wrthin a range of similar size and/or shape and containing one or more actι\ e agents and one or more excipients, preferably including a hydrophobic material as described herein In this regard, the melt-extruded multiparticulates will be of a range of from about 0 1 to about 12 mm m length and have a diameter of from about 0 1 to about 5 mm In addition, it is to be understood that the melt-extruded multiparticulates can be any geometrical shape withm this size range Alternatively, the extrudate may srmply be cut into desired lengths and divided into unit doses of the therapeutically active agent without the need of a spheronization step In one prefened embodiment, oral dosage fonns are prepared to include an effective amount of melt-extruded multiparticulates ithm a capsule For example, a plurality of the melt-extruded multiparticulates may be placed m a gelatin capsule m an amount sufficient to provide an effective sustained release dose when ingested and contacted by gastric fluid In another prefened embodiment, a suitable amount of the multiparticulate extiudate is combined with the coated opioid antagonist particles and compiessed into an oral tablet using conventional tabletmg equipment using standard techniques Techniques and compositrons for makmg tablets (compressed and molded), capsules (hard and soft gelatin) and pills are also described in Remington's Pharmaceutical Sciences, (Arthur Osol editor), 1553-1593 (1980), mcoφorated by reference herein In yet another prefened embodrment, the coated opioid antagonist particles are added during the extrusion process and the extrudate can be shaped into tablets as set forth in U S Patent No 4,957,681 (Klimesch, et al ), described in additional detail abo\ e and hereby incoφorated by reference Optionally, the sustained release melt-extruded multiparticulate systems or tablets can be coated, or the gelatin capsule can be further coated, wrth a sustained release coating such as the sustained release coatings described above Such coatings preferably include a sufficient amount of hydrophobic matenal to obtain a weight gam level from about 2 to about 30 percent, although the overcoat may be greater depending upon the physical properties of the particular opioid analgesic compound utilized and the desired release rate, among othei things The melt-extruded unit dosage forms ofthe present invention may further include combinations of melt-extruded multiparticulates containing one or more of the therapeutically active agents disclosed above before being encapsulated Furthermore, the unit dosage forms can also include an amount of an immediate release opioid agonist for prompt therapeutic effect The immediate release opioid agonist may be incoφorated, e g . as sepaiate pellets withm a gelatin capsule, or may be coated on the surface of the multiparticulates after preparation ofthe dosage forms (e g , controlled release coating or matrix-based) The unit dosage forms ofthe present mvention may also contain a combination of controlled release beads and matrix multiparticulates to achieve a desired effect The sustamed release formulations ofthe present invention preferably slowly release the opiord agonist, e g , when ingested and exposed to gastric fluids, and then to intestinal fluids The sustained release profile of the melt-extruded formulations ofthe im ention can be altered, for example, by varying the amount of retardant, I e , hydrophobic material, by varying the amount of plasticizer relative to hydrophobic material, by the inclusion of additional ingredients or excipients, by altering the method of manufacture, etc In other embodiments of the invention, the melt exti tided material is prepaied without the inclusion ofthe opioid agonist and/or coated opioid antagonist particles, which are added thereafter to the extrudate Such formulations typically will have the drugs blended together with the extruded matrix matenal, and then the mixture would be tableted m ordei to provide a slow release ofthe opioid agonist Such formulations may be advantageous, foi example, when the therapeutically active agent included in the formulation is sensitive to tempeiatuies needed for softening the hydrophobic material and/ or the retardant material DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS The following examples illustrate various aspects of the piesent invention They aie not to be construed to limit the claims in any manner whatsoever EXAMPLE 1 In Example 1, a substantially non-releasable form of an opioid antagonist (naltiexone HCl) is prepared by coating naltrexone particles with a coating that renders the antagonist substantially non-releasable A- c \ FORMULA: * Remains in product as residual moisture only. PROCESS: 1. Solution Preparation Dissolve the Naltrexone HCl in Purified Water. Once dissolved, add the Opadry White and continue mixing until a homogeneous dispersion is yielded. 2. Loading Apply the above dispersion onto the Sugar Spheres using a fluid bed coating machine. 3. Overcoating Prepare an overcoating solution by dispersing Opadry White in Purified Water. Apply this dispersion over the sugar spheres loaded with Naltrexone HCl using a fluid bed coating machine. 4. Retardant Coating Prepare the non-release coating solution by mixing the Eudragit RS30D, Triethyl Citrate, Talc, and Purified Water. Apply this dispersion over the loaded and overcoated sugar spheres using a fluid bed coating machine. 5. Overcoating Prepare a second overcoating solution by dispersing Opadry White in Purified Water. Apply this dispersion over the non- release coated naltrexone spheres using a fluid bed coating machine 6. Curing Cure the spheres at 45°C for approximately 48 hours. SD EXAMPLE 2 In Example 2, a substantially non-releasable form of an opioid antagonist (naltrexone HCl) is prepared as naltrexone HCl containing granulates. The granulates are comprised of naltrexone HCl dispersed in a matrix that renders the antagonist substantially non-releasable. FORMULA: * Used as a vehicle for application of PLGA polymer. PROCESS: 1. Solution Preparation Dissolve PLGA in Ethyl Acetate by mixing. 2. Granulation Place the Naltrexone HCl, and Dicalcium Phosphate in a fluid bed coating machine and granulate by spraying the above solution. EXAMPLE 3 In Example 3, a substantially non-releasable form of an opioid antagonist (naltrexone HCl) is prepared as naltrexone HCl extruded pellets. FORMULA: PROCESS: 1. Milling Pass stearyl alcohol flakes through an impact mill. 2. Blending Mix Naltrexone HCl, Eudragit, and milled Stearyl Alcohol in a twin shell blender. 3. Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant strands on a conveyor. 4. Cooling Allow the strands to cool on the conveyor. 5. Pelletizing Cut the cooled strands into pellets using a Pelletizer. 6. Screening Screen the pellets and collect desired sieve portion. :- EXAMPLE 4 Hydrocodone Bitartrate Controlled Release Tablets with Naltrexone HCl Beads * Remams in product as residual moisture only. PROCESS: 1 Milling Pass the Stearyl Alcohol flakes through an occillating mill 2. Blending Mix the Hydrocodone Bitartrate, milled Stearyl Alcohol, Anhydrous Dicalcium Phosphate, Microcrystalline Cellulose, and Glyceryl Behenate m a twin shell blendei Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant heated matenal on a conveyoi 4. Cooling Allow the extrudate to cool on the conveyor 5. Milling Mill the cooled extrudate using an occillating mill 6 Blending Blend the milled extrudate, naltrexone HCl beads (fiom Example 1), and Magnesium Stearate Compression Compress the resultant granulation using a tablet press 8. Coating Prepare a film coating solution by dispersing the Opadry in Purified Water and applying it to the tablet cores EXAMPLE 5 Hydrocodone Bitartrate Controlled Release Tablets with Naltrexone HCl Granulation * Remains in product as residual moisture only PROCESS 1 Milling Pass the Stearyl Alcohol flakes through an occillating mill Blending Mix the Hydrocodone Bitartrate, milled Stearyl Alcohol, Anhydrous Dicalcium Phosphate, Microcrystalline Cellulose, and Glyceryl Behenate in a twin shell blender Extrusion Continuously feed the blended matenal rnto a twin screw extruder and collect the resultant heated material on a conveyor 4 Cooling Allow the extrudate to cool on the conveyor 5 Milling Mill the cooled extrudate using an occillating mill 6 Blending Blend the milled extrudate, Naltrexone HCl granulation (from Example 2), and Magnesium Stearate 7 Compression Compress the resultant granulation using a tablet press 8 Coating Prepare a film coating solution by dispersing the Opadry in Punfied Water and applying it to the tablet cores *f EXAMPLE 6 Oxvcodone HCl Controlled Release Tablets with Naltrexone HCl Beads * Remains m product as residual moisture only. PROCESS. 1. Solution Preparation Plasticize the Eudragit with Tnacetm by mixing 2. Granulation Place Oxycodone HCl, Spray Dned Lactose, and Povidone into a fluid bed granulator and apply the above solution 3. Milling Pass the granulation through a rotating impeller mill. 4. Drying Dry granulation if moisture content is too high 5. Waxing Melt Stearyl Alcohol and wax the above granulatron by adding melted Stearyl Alcohol onto granulation while mixing 6. Cooling Cool the waxed granulation in a fluid bed dryer. 7. Milling Pass the cooled waxed granulation through a rotating impeller mill. 8. Blending Blend the milled waxed granulation, Talc, Magnesium Stearate. and Naltrexone HCl beads (from Example 1) 9. Compression Compress the resultant granulation using a tablet press 10. Coating Prepare a film coating solution by dispersing the Opadry m Purified Water and applying it to the tablet cores P? EXAMPLE 7 Oxcodone HCl Controlled Release Tablets with Naltrexone HCl Granulation * Remains in product as residual moisture only. PROCESS: 1. Solution Preparation Plasticize the Eudragit with Tnacetm by mixing. 2. Granulation Place Oxycodone HCl, Spray Dried Lactose and Povidone into a fluid bed granulator and apply the above solution. 3. Milling Pass the granulation through a rotating impeller mill. 4. Drying Dry granulation if moisture content is too high 5. Waxing Melt Stearyl Alcohol and wax the above granulation by adding melted Stearyl Alcohol onto granulation while mixing 6. Cooling Cool the waxed granulation in a fluid bed dry er. 7. Milling Pass the cooled waxed granulation through a rotating impeller mill. Blending Blend the milled waxed granulation, Talc, Magnesium Stearate, and Naltrexone HCl granulation (from Example 2). 9. Compression Compress the resultant granulation using a tablet press. 10. Coating Prepare a film coating solution by dispersing the Opadry in Purified Water and applying it to the tablet cores. EXAMPLE 8 Hydromorphone HCl Controlled Release Capsules with Naltrexone HCl Extruded Pellets FORMULA PROCESS 1 Mrllrng Pass Stearyl Alcohol flakes through an impact mill 2 Blending Mix Hydromoφhone HCl, Eudragit, Ethycellulose and milled Stearyl Alcohol in a twin shell blender 3 Extrusion Continuously feed the blended material into a tw in screw extruder and collect the resultant strands on a co eyor 4 Cooling Allow the strands to cool on the conveyor 5 Pelletizmg Cut the cooled strands into pellets using a Pelletizer 6 Screening Screen the pellets and collect desired sieve portion 7 Encapsulation Fill the extruded Hydromoφhone HCl pellets at 120 mg and Naltrexone HCl pellets (from Example 3) at 240 mg into hard gelatin capsules 5H EXAMPLE 9 Hydrocodone Bitartrate Controlled Release Tablets with Naltrexone HCl Beads * Remains in product as residual moisture only. PROCESS: 1. Milling Pass the Stearyl Alcohol flakes through an occillating mill. 2. Blending Mix the Hydrocodone Bitartrate, milled Stearyl Alcohol, Anhydrous Dicalcium Phosphate, Microcrystalline Cellulose, and Glyceryl Behenate in a twin shell blender. 3. Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant heated material on a conveyor. 4. Cooling Allow the extrudate to cool on the conveyor. 5. Milling Mill the cooled extrudate using an occillating mill. 6. Blending Blend the milled extrudate, Naltrexone HCl beads (from Example 1), and Magnesium Stearate. 7. Compression Compress the resultant granulation using a tablet press. 8. Coating Prepare a film coating solution by dispersing the Opadry in Purified Water and applying it to the tablet cores. EXAMPLE 10 Hydrocodone Bitartrate Controlled Release Tablets with Naltrexone HCl Granulation * Remains in product as residual moisture only. PROCESS: 1. Milling Pass the Stearyl Alcohol flakes through an occillating mill. 2. Blending Mix the Hydrocodone Bitartrate, milled Stearyl Alcohol, Anhydrous Dicalcium Phosphate, Microcrystalline Cellulose, and Glyceryl Behenate in a twin shell blender. 3. Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant heated material on a conveyor. 4. Cooling Allow the extrudate to cool on the conveyor. 5. Milling Mill the cooled extrudate using an occillating mill. 6. Blending Blend the milled extrudate, Naltrexone HCl granulation (from Example 2), and Magnesium Stearate. 7. Compression Compress the resultant granulation using a tablet press. 8. Coating Prepare a film coating solution by dispersing the Opadry in Purified Water and applying it to the tablet cores. EXAMPLE 11 Oxvcodone HCl Controlled Release Tablets with Naltrexone HCl Beads * Remains in product as residual moisture only. PROCESS: 1. Solution Preparation Plasticize the Eudragit with Triacetin by mixing. 2. Granulation Place Oxycodone HCl, Spray Dried Lactose, and Povidone into a fluid bed granulator and apply the above solution. 3. Milling Pass the granulation through a rotating impeller mill. 4. Drying Dry granulation if moisture content is too high. 5. Waxing Melt Stearyl Alcohol and wax the above granulation by adding melted Stearyl Alcohol onto granulation while mixing. 6. Cooling Cool the waxed granulation in a fluid bed dryer. 7. Milling Pass the cooled waxed granulation through a rotating impeller mill. Blending Blend the milled waxed granulation, Talc, Magnesium Stearate, and Naltrexone HCl beads (from Example 1). 9. Compression Compress the resultant granulation using a tablet press. 10. Coating Prepare a film coating solution by dispersing the Opadry in Purified Water and applying it to the tablet cores. r EXAMPLE 12 Oxycodone HCl Controlled Release Tablets with Naltrexone HCl Granulation * Remains in product as residual moisture only. PROCESS: 1. Solution Preparation Plasticize the Eudragit with Tnacetm by mixing 2 Granulation Place Oxycodone HCl, Spray Dried Lactose, and Povidone into a fluid bed granulator and apply the above solution 3. Milling Pass the granulation through a rotating impeller mill 4. Drying Dry granulation if moisture content is too high 5. Waxmg Melt Stearyl Alcohol and wax the above granulation by adding melted Stearyl Alcohol onto granulation while mixing 6. Cooling Cool the waxed granulation m a fluid bed dryer 7. Milling Pass the cooled waxed granulation through a rotating impeller mill 8 Blending Blend the milled waxed granulation, Talc, Magnesium Stearate, and Naltrexone HCl granulation (from Example 2) 9. Compression Compress the resultant granulation using a tablet press 10 Coating Prepare a film coating solution by dispersing the Opadry m Purified Water and applying it to the tablet cores \ WO 01/58451 PCT/TJSOl/04346 EXAMPLE 13 Hydromorphone HCl Controlled Release Capsules with Naltrexone HCl Extruded Pellets FORMULA: PROCESS: 1. Milling Pass stearyl alcohol flakes through an impact mill. 2. Blending Mix Hydromoφhone HCl, Eudragit, Ethycellulose and milled Stearyl Alcohol in a twin shell blender. 3. Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant strands on a conveyor. 4. Cooling Allow the strands to cool on a Conveyor. 5. Pelletizing Cut the cooled strands into pellets using a Pelletizer. 6. Screening Screen the pellets and collect desired sieve portion. 7. Encapsulation Fill the extruded Hydromoφhone HCl pellets at 120.0 mg and Naltrexone HCl pellets (from Example 3) at 240 mg into hard gelatin capsules. EXAMPLE 14 Controlled Release Oxycodone Hydrochloride 10 mg Tablets— Organic Manufacture Oxycodone hydrochloride (10 mg/tablet) and spray dried lactose (71.25 mg/tablet) are transferred into an appropriate sized mixer and mix for approximately 6 minutes. Eudragit " RS PM powder (6 mg/tablet) is dispersed in ethanol. While the powders are mixing, the powders are granulated with the dispersion and the mixing continued until a moist granular mass is formed. Additional ethanol is added if needed to reach granulation end point. The granulation is transfened to a fluid bed dryer and dried at 30 C, and then passed through a 12-mesh screen. The remaining Eudragit RS PM (9 mg/tablet) is dispersed in a solvent of 90 parts ethanol and 10 parts purified water; and sprayed onto the granules in the fluid bed granulator/dryer at 30 C. Next, the granulate is passed through a 12-mesh screen. Stearyl alcohol (25 mg/tablet) is melted at approximately 60-70 C. The warm granules are returned to the mixer. While mixing, the melted stearyl alcohol is added. The coated granules are removed from the mixer and allowed to cool. Thereafter, they are passed through a 12-mesh screen. Next, the granulate is mixed with naloxone particles (approximately 1-5 mg per tablet) coated with a coating that renders naloxone substantially non-releasable, and pharmaceutically desirable tabletting excipients, e.g., talc and magnesium stearate in a suitable blender and compressed into tablets. The naloxone particles have a diameter of about 0.5 to 2 mm. The naloxone particles coated with a coating that renders naloxone substantially non-releasable may be prepared by spraying onto the particles the coating composition comprising a cellulose polymer or an acrylic polymer that is insoluble in water and impermeable to naloxone. The suitable particles include granules, pellets, spheroids or beads comprising naloxone. When the particles are beads or pellets, they may be prepared by dissolving the naloxone in a solution and spraying it onto inert pellets or beads. Preferably, the coating composition comprises Eudragit " RS, which may be used in the form of an aqueous suspension and in combination with a plasticizer such as, e.g.. acetyl triefhylcitrate and/or acetyl tributyl citrate. c3 Preferably, the coating composition comprises Eudragit RS, which may be used m the form of an aqueous suspension and m combination with a plasticizer such as, e g , acetyl tπethylcitrate and/or acetyl tπbuty 1 citrate EXAMPLE 15 Method Of Treating Pam The oral dosage form accordmg to the present invention may be admimstered to a patient to provide pam relief The oral dosage form may comprrse an orally effective amount of an opioid agonist and an opioid antagonist that is rendered substantially non-releasable When the oral dosage form is administered orally and delivered to the gastrointestinal tract of a patient in need of pam therapy, the opioid agonist is released from the dosage fonn during normal digestion, providing analgesia to the patient But the opioid antagonist, because it has been rendered substantially non-releasable is substantially not released during its transit through the gastrointestinal system Preferably, the substantially non-releasable form ofthe antagonist is resistant to laxatives (mineral oil) used to manage delayed colomc transit , or achlorhydna states Patients who take the oral dosage form as directed, without tampering with it (e g by mechanical agitation, heating, or dissolution m a solvent), will not have the opioid antagonist absorbed in sufficient amount during any time interval dunng the dosing ofthe formulation such that the analgesic effectiveness of the opioid agonist is reduced or eliminated by the antagonist In other words, the amount of opioid antagonist released from the dosage form (w hen orally administered mtact) and absorbed from the gastrointestinal tract and accumulated in the patient's body, does not rise to a level which significantly impacts or changes on the analgesic efficacy ofthe dose of opioid agonist included in the dosage form M EXAMPLE 16 Method Of Preventing Abuse Of An Opioid Agonist The oral dosage form accordmg to the present invention may be used to prevent the abuse potential of an opioid agonist contained therein The oial dosage form compnses an opioid agonist in combination with an opioid antagonist The opioid antagonist is piesent m a form that is substantially non-releasable during digestion Thus, when the oial dosage form is delivered to the gastrointestinal tract orally as intended, without ha\ mg been tampered with, the antagonist is substantially prevented from being released into the gastrointestinal system But if the oral dosage form is tampered with, e g , by mechanical agitation (e g , crushing, shearing, grinding), heat (e g , temperatures of greater than 45 C , preferably between 45 to 50 C), or dissolution ofthe dosage form in a solvent (with or without heating), the dosage form is tainted by the opioid antagonist, which is now made available to blunt the opioid effects Thus, when the dosage form is chewed, crushed, heated or dissolved m a solvent, and then administered orally, intranasally, parenterally or sublingually, the effect of the opioid agonist is at least partially blocked by the opioid antagonist EXAMPLE 17 In this human study, 12 moφhme-dependent subjects were evaluated for precipitated withdrawal after administration of hydrocodone immediate release tablets given concomitantly with a dose of naltrexone ranging from 0 25 to 8 mg The experimental design was single blind, single-dose, placebo-controlled with an ascending naltrexone dose After administration ofthe study medications, subjective and physiological measurements of abuse liability and withdrawal were made across a 32-fold range of naltrexone doses The data suggest that at a 1 mg naltrexone dose, opioid-dependent subjects demonstrate less liking of the agonist relative to the combination with placebo and achieved a plasma concentration resulting in 50% ofthe maximal withdrawal symptom score EXAMPLE 18 This was a randomized, double blind placebo controlled trial examining the threshold of withdrawal induced by immediate-release naltrexone in 12 methadone-dependent subjects While the study was in progress, an mtenm analysis shows that 0 5 mg of naltrexone was able to elicit the signs and symptoms of withdrawal in this population These studies suggest that the dose of naltrexone needed to elicit withdra al symptoms m opioid dependent subjects lies between 0 25 and 1 mg EXAMPLE 19 This is a randomized single blind, single dose, placebo controlled 10-way ei trial examining the effect of naltrexone on the subjective and physiological effects of 15 mg hydrocodone in 16 normal subjects Doses of naltrexone ranged from 0 4 to 12 8 mg In this study, 0 4 mg of naltrexone was able to antagonize several ofthe centrally mediated opioid effects of hydrocodone, including pupillary miosis Based on this data, substantially lower doses below 0 25 mg of naltrexone will demonstrate little antagonism of the concomitant agonist This is supported by the absence of withdrawal signs observed m subjects m example 17 receiving the 0 25-mg The clinical data for examples 17, 18 and 19 suggest that bio-available, immediate- release doses of 0 125 mg of naltrexone (or equiv alent prompt release from a controlled release dosage form) will not affect analgesia to any significant degree, while larger prompt release of bio-available drug (0 25 mg or greater) will do so These clinical data show that a loading of naltrexone into the opioid matnx for thrs example at a ratio of 1 15 to 1 30 mg naltrexone/mg hydrocodone, and that the tampered mtact release ratio is at least 4 1 and preferably hrgher Or alternatively, it can be defined that less than 0 25 mg of naltrexone is released from the mtact dosage form, and 0 25 mg or greater naltrexone rs released from the crushed dosage form G-(r EXAMPLE 20 Naltrexone HCl Beads FORMULA: Bead Manufacturing Procedure 1. Dissolve naltrexone HCl and Opadry Clear in water. Spray the dnig solution onto non-pareil beads in a fluid bed coater with Wurster insert. 2. Disperse Eudragit L30D, Tributyl citrate, and talc in water. Spray the dispersion onto the drug-loaded beads in the fluid bed coater. 3. Disperse Eudragit RS30D, tributyl citrate, and talc in water. Spray the dispersion onto the beads in the fluid bed coater. 4. Dissolve Opadry Clear in water. Spray the solution onto the beads in the fluid bed coater. 5. Cure the beads at 60°C for 24 hours. DISSOLUTION METHOD 1. Apparatus- USP Type II (Paddle), 75 φm at 37°C 2. Sampling Time: 1, 2, 4, 8, 12, 24, 36 3. Media: SGF for one hour/ SIF thereafter Analytical Method: High Performance Liquid Chromatography on Results and Discussion: The beads (108 mg) were found to have the following dissolution results: Time (hr) 1 2 4 12 24 36 Mean % nd nd nd nd 6.0 10.0 dissolved nd=none detected The dissolution results show that only about 10%o naltrexone HCl (0.06 mg) of naltrexone HCl was released after 36 hours in the dissolution bath. These beads will not be bioavailable if taken unbroken orally. Naltrexone HCl is very water-soluble. It tends to migrate through the sustained release film during aqueous film coating process (step 3). If migration occurs during this coating step, the film will become porous during dissolution and the drug release rate would be relatively rapid. The anionic coating (step 2) forms a water insoluble complex layer with the protonated naltrexone HCl salt and would prevent the drug from migrating through the subsequent sustained release coating. Dissolution of broken beads Simulated tampering process About 108 mg of naltrexone beads was ground in a mortar and pestle to powder for the dissolution study. Dissolution Method- same as above Results and Discussion: The broken beads (108 mg) were found to have the following dissolution results: Time (hr) 0.25 0.5 1 Mean % 91 100 104 dissolved We can thus see at hour 1, from the intact beads, there is no detectable NTX released, yet when crushed, all the NTX, 0.6 mg is released. This is graphically represented in Figure ( cβ 1. Thus the ratio of cnished/ mtact at hour 1 is 100.0 and this is greater than the criteria of > 4:1 as concluded from examples 17, 18 and 19 EXAMPLE 21 Oxycodone IR Capsules with Naltrexone beads FORMULA: * To blind the OxylR beads, the naltrexone beads would need to use Opadry Butterscotch as the seal coat m Step 4, Example 20. Manufacturing Procedure 1. Dissolve oxycodone HCl and HPMC in water Spray the drug solution onto nonpareil beads in a fluid bed coater with Wurster insert 2. Dissolve the colored Opadry in water. Film coat the drug-loaded beads m the fluid bed coater. 3. Mix equal amount of OxylR beads and naltrexone beads. Encapsulate in hard gelatin capsules. ( , EXAMPLE 22 Morphine Sulfate Controlled Release Capsules with Naltrexone beads FORMULA: * To blind the MSCR beads, the naltrexone beads would need to use Opadry blue as the seal coat in Step 4, Example 22. Manufacturing Procedure 1. Disperse povidone and Eudragit RS30D in water. Blend moφhine sulfate and lactose. 2. Load beads in Rotor processor. Spray the drug powder blend and the binder solution onto beads. 3. Film-coat the above beads in the Rotor processor. 4. Disperse Eudragit RS30D, RL 30D, Triethyl citrate, talc and triethyl citrate in water. Coat the above beads in a fluid bed coated with Wurster insert. 5. Cure the beads (MSCR beads). 6. Mix equal amount of MSCR beads and naltrexone beads. Encapsulate in hard gelatin capsules. no EXAMPLE 23 Naltrexone HCl Extruded Pellets FORMULA: PROCESS: 1. Milling Pass stearyl alcohol flakes through a mill. 2. Blending Mix Naltrexone HCl, Eudragit, milled Stearyl Alcohol, Stearic Acid and BHT in a twin shell blender. 3. Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant strands on a conveyor. 4. Cooling Allow the strands to cool on a Conveyor. 5. Pelletizing Cut the cooled strands into 1mm pellets using a Pelletizer. 6. Screening Screen the pellets and collect desired sieve portion. DISSOLUTION METHOD 1. Apparatus- USP Type II (Paddle), 75 φm at 37°C 2. Sampling Time: 1, 2, 4, 8, 12, 24, 36 3. Media: SGF for one hour/ SIF thereafter 4. Analytical Method: High Performance Liquid Chromatography Results: Simulated Tampering Process Naltrexone Pellets were ground in a mortar and pestle to powder for the dissolution study. Dissolution Method: Same as above Results: ni Thus the release of the intact pellets is 0.026 mg at hour 1, and when crushed is 0.67 mg at hour 1. This ratio of crushed to intact is also greater than 4:1. This is graphically represented in Figure 2. EXAMPLE 24 Naltrexone HCl Extruded Pellets FORMULA: PROCESS: 1. Milling Pass stearyl alcohol flakes through a mill. 2. Blending Mix Naltrexone HCl, Eudragit, milled Stearyl Alcohol, Dibasic Calcium Phosphate and BHT in a twin shell blender. 3. Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant strands on a conveyor. 4. Cooling Allow the strands to cool a Conveyor. 5. Pelletizing Cut the cooled strands into pellets using a Pelletizer. 6. Screening Screen the pellets and collect desired sieve portion. DISSOLUTION METHOD 4. Apparatus- USP Type II (Paddle), 75 φm at 37°C 5. Sampling Time: 1, 2, 4, 8, 12, 24, 36 6. Media: SGF for one hour/ SIF thereafter 7. Analytical Method: High Performance Liquid Chromatography η . Results: Simulated Tampering Process Naltrexone Pellets were ground in a mortar and pestle to powder for the dissolution study. Dissolution Method: Same as above Results: Thus the release of the intact pellets is 0.062 mg at hour 1, and when crushed is 0.728 mg at hour 1. This ratio of crushed to intact is also greater than 4:1. This is graphically represented in Figure 24. 13 EXAMPLE 25 Possible Hydromorphone HCl CR Capsules with Naltrexone HCl Extruded Pellets FORMULA: PROCESS: 1. Milling Pass Stearyl Alcohol flakes through an impact mill. 2. Blending Mix Hydromoφhone HCl, Eudragit, Ethycellulose and milled Stearyl Alcohol in a twin shell blender. 3. Extrusion Continuously feed the blended material into a twin screw extruder and collect the resultant strands on a conveyor. 4. Cooling Allow the strands to cool a Conveyor. 5. Pelletizing Cut the cooled strands into pellets using a Pelletizer. 6. Screening Screen the pellets and collect desired sieve portion. 7. Encapsulation Fill the extruded Hydromoφhone HCl pellets at 120 mg and Naltrexone pellets (from example 23) at 121 mg into hard gelatin capsules. Example 26 Possible Hydromorphone HCl CR Capsules with Naltrexone HCl Extruded Pellets FORMULA: • H PROCESS: 1 Milling Pass Stearyl Alcohol flakes through an impact mill 2 Blending Mix Hydromoφhone HCl, Eudragit, Ethycellulose and milled Stean ] Alcohol m a twin shell blender Extrusion Contmuously feed the blended matenal into a twin screw extruder ai.d collect the resultant strands on a conveyor 4 Cooling Allow the strands to cool a Conveyor 5 Pelletizmg Cut the cooled strands into pellets using a Pelletizer 6 Screening Screen the pellets and collect desired sieve portion 7 Encapsulation Fill the extruded Hydromoφhone HCl pellets at 120 mg and Naltrexone pellets (from example 24) at 127 mg mto hard gelatin capsules Example 27A Naltrexone CR Beads A Naltrexone controlled release bead is developed which can be mcoφorated into opioid controlled release granulation and the mixture is then compressed mto tablets Oxycodone HCl controlled release granulation is used with naltrexone beads as an example 16 Bead Manufacturing Procedure 1. Dissolve naltrexone HCl and HPMC in water. Spray the drug solution onto nonpareil beads in a fluid bed coater with Wurster insert. 2. Disperse Eudragit L, Tributyl citrate, and talc in water. Spray the dispersion onto the drug-loaded beads in the fluid bed coater. 3. Disperse Eudragit RS, tributyl citrate, and talc in water. Spray the dispersion onto the beads in the fluid bed coater. 4. Dissolve HPMC in water. Spray the solution onto the beads in the fluid bed coater. 5. Cure the beads at 60°C for 24 hours. DISSOLUTION METHOD 1. Apparatus- USP Type II (Paddle), 75 φm at 37°C 2. Sampling Time: 1, 2, 4, 8, 12, 24, 36 3. Media: SGF for one hour/ SIF thereafter 4. Analytical Method: High Performance Liquid Chromatography Results and Discussion: Naltrexone dissolution from intact beads Time (hr) 1 4 8 12 24 36 Mean % 2 2 4 5 6 33 dissolved Naltrexone dissolution from crushed beads Time (hr) 100 dissolved Manufacturing Procedure (Oxy/NX CR tablet) 1 Spray the Eudragit tnacetm dispersion onto the Oxycodone HCl, spray dried lactose and povidone using a fluid bed granulator 2 Discharge the granulation and pass through a mill 3 Melt the stearyl alcohol and add to the milled granulation using a mill Allow to cool 4 Pass the cooled granulation through a mill 5 Lubricate the granulation with talc and magnesium stearate Using a mixei 6 Mix naltrexone beads with the above granulation and compress mto tablets DISSOLUTION METHOD 1 Apparatus- USP Type II (Paddle), 50 φm at 37°C 2 Sampling Time 1, 2, 4, 8, 12, 24, 36 3 Media 900 ml pH 6 5 phosphate buffer 4 Analytical Method High Performance Liquid Chromatography The Oxy/NX CR tablets ere found to have the following dissolution results Naltrexone dissolution from intact tablet Tune (hr) 1 4 8 12 24 36 Mean % 1 3 9 15 25 36 dissolved Naltrexone dissolution from crushed tablet Mean % 95 dissolved

Claims: WHAT IS CLAIMED IS: 1. An oral dosage form comprising (i) an opioid agonist in releasable fonn and (ii) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio ofthe amount of antagonist released from said dosage form after tampering to the amount of said antagonist released from said intact dosage form is about 4: 1 or greater, based on the in-vitro dissolution at 1 hour of said dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C wherein said agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers. 2. An oral dosage form comprising (i) an opioid agonist in releasable form and (ii) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio ofthe amount of antagonist released from said dosage form after tampering to the amount of said antagonist released from said intact dosage form is about 4:1 or greater, based on the in-vitro dissolution at 1 hour of said dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C wherein said antagonist is in the form of multiparticulates individually coated with a sequestering material which substantially prevents release ofthe antagonist. 3. An oral dosage form comprising (i) an opioid agonist in releasable form and (ii) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the ratio ofthe amount of antagonist released from said dosage form after tampering to the amount of said antagonist released from said intact dosage form is about 4: 1 or greater, based on the in-vitro dissolution at 1 hour of said dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C wherein said antagonist is dispersed in a matrix comprising a sequestering material which substantially prevents the release of the antagonist. 1Q An oral dosage form compnsing (l) an opioid agonist in releasable form and (n) a sequestered opioid antagonist which is substantially not released w hen the dosage form rs administered mtact, such that the ratio ofthe amount of antagonist contained in said intact dosage form to the amount of said antagonist released from said mtact dosage form after 1 hour is about 4 1 or greater, based on the m-vitro dissolution at 1 hour of said dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C wherein said agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers An oral dosage form comprising (l) an opioid agonist in a releasable fonn, and (n) a sequestered opioid antagonist which is substantially not released when the dosage form is administered intact, such that the amount of antagonist released from said intact dosage form after 1 hour is less than an amount bioequivalent to 0 25 mg naltrexone and the amount of said antagonist released after 1 hour from said dosage form after tampenng is an amount bioequivalent to 0 25 mg naltrexone or more, said release based on the dissolution at 1 hour of said dosage form in 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C, wherein said agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers An oral dosage form compnsing (l) an opioid agonist m a releasable form, and (n) sequestered naltrexone or a pharmaceutically acceptable sat thereof which is substantially not released when the dosage form rs administered mtact, such that the amount of naltexone released from said mtact dosage form after 1 hour is less than 0 25 mg and the amount of said naltrexone released after 1 hour from said dosage form after tampenng is 0 25 mg or more, said release based on the dissolution at 1 hour of said dosage form m 900 ml of Simulated Gastric Fluid using a USP Type II (paddle) apparatus at 75 φm at 37 degrees C, wherein said agonist and naltrexone are interdispersed and are not isolated from each other in two distinct layers An oral dosage form compnsing (l) a therapeutic effect of an opioid agonist, and (n) a sequestered opioid antagonist, such that at 1 hour after oral admmrstration, said dosage form releases not more than 25% of said antagonist, said dosage form providing analgesia and said released antagonist not affecting analgesic efficacy, wherein said agonist and antagonist are interdispersed and are not isolated from each other in two distinct layers An oral dosage fonn comprising (I) an opioid agonist m a releasable form, and an (n) opioid antagonist m substantially non-releasable form wherein said antagonist is in the form of multipartrculates individually coated with a material that substantially prevents release of the antagonist An oral dosage form comprising (l) an opioid agonist in a releasable foπn, and an (n) opioid antagonist in substantially non-releasable form wherein said antagonist is dispersed in a matnx compnsing a material that substantially prevents the release of the antagonist The oral dosage form of claims 1-4 wherein said ratio is 10 1 or greater The oral dosage form of clarms 1-4 wherein said ratio is 50 1 or greatei The oral dosage form of claims 1-4 wherein said ratio is 100 1 or greater The oral dosage form of clarm 6 wherein said intact dosage form releases at least 0 025 mg naltrexone at 1 hour The oral dosage form of claims 1-5 and 7-9 wherein said mtact dosage foπn piovides at least an amount of antagonist bioequivalent to 0 025 mg naltrexone at 1 hour The oral dosage form of claim 5 wherein the amount of antagonist released aftei 1 hour from said tampered dosage form rs an amount bioequivalent to 0 5 mg naltrexone or more The oral dosage form of claims 5 and 15 wherein the amount of antagonist released after 1 hour from said mtact dosage form is an amount bioequivalent to 0 125 mg naltrexone or less ®0 17. The oral dosage form of claim 6 wherein the amount of antagonist released after 1 hour from said tampered dosage form is 0.5 mg naltrexone or more. 18. The oral dosage form of claims 6 and 17 wherein the amount of antagonist released after 1 hour from said intact dosage form is 0.125 mg naltrexone or less. 19. The oral dosage form of claims 1-9, wherein the opioid agonist is selected from the group consisting of moφhine, hydromoφhone, hydrocodone, oxycodone, codeine, levoφhanol, meperidine, methadone, oxymoφhone, buprenoφhine, fentanyl and derivatives thereof, dipipanone, heroin, tramadol, etoφhine, dihydroetoφhine, butoφhanol, levoφhanol, pharmaceutically acceptable salts thereof and mixtures thereof. 20. The oral dosage form of claim 19, wherein the opioid agonist is selected from the group consisting of oxycodone, hydrocodone and pharmaceutically acceptable salts thereof. 21. The oral dosage form of claims 1-5 and 7-9, wherein the opioid antagonist is selected from the group consisting of naltrexone, naloxone, nalmephene, cyclazocine, levalloφhan, pharmaceutically acceptable salts thereof and mixtures thereof. 22. The oral dosage form of claim 21, wherein the opioid antagonist is selected from the group consisting of naltrexone, naloxone, nalmephene, pharmaceutically acceptable salts thereof and mixtures thereof. 23. The oral dosage form of claim 22, wherein the opioid antagonist comprises naltrexone or a pharmaceutically acceptable salt thereof. 24. The oral dosage form of claims 2 and 8, wherein the material comprises a cellulose polymer or an acrylic polymer that is insoluble in the gastrointestinal tract and impermeable to the opioid antagonist contained within the coating. 25. The oral dosage form of claim 24, wherein the cellulose polymer is selected from the group consisting of ethylcellulose, cellulose acetate, cellulose propionate, cellulose acetate propionate, cellulose acetate butyrate, cellulose acetate phthalate, and mixtures thereof. 26. The oral dosage form of claim 24, wherein the acrylic polymer is selected from the group consisting of acrylic acid and methacrylic acid copolymers, methyl methacrylate copolymers, ethoxyethyl methacrylates, cyanoethyl methacrylate, poly(acrylic acid), poly(methacrylic acid), methacrylic acid alkylamide copolymer, polyrinefhyl methacrylate), polymethacrylate, poly(methyl methacrylate) copolymer, polyacrylamide, aminoalkyl methacrylate copolymer, poly(methacrylic acid anhydride), and glycidyl methacrylate copolymers. 27. The oral dosage form of claims 1-9, wherein the dosage form provides sustained- release ofthe opioid agonist. 28. The oral dosage form of claim 27, wherein the dosage fonn is a sustained-release tablet or a sustained-release capsule. 29. The oral dosage form of claim 2 and 8 wherein said multiparticulates are in the form of inert beads coated with said antagonist and overcoated with said material. 30. The oral dosage form of claims 2 and 8 wherein said multiparticulates are in the form of a granulation comprising said antagonist and said material. 31. The oral dosage form of claims 2 and 8 wherein said multiparticulates are dispersed in a matrix comprising said opioid agonist. 32. The oral dosage form of claims 2 and 8 wherein said multiparticulates are contained in a capsule with said opioid agonist. 33. The oral dosage form of claims 3 and 9 wherein said matrix is in the form of pellets. 8 C? ' a. 34. The oral dosage form of claim 33 wherein said pellets are dispersed m a matrix comprising said opioid agonist 35 The oral dosage form of claim 33 wherein said pellets are contained m a capsule \\ ith said opioid agonist 36. The oral dosage form of claims 1-9 wherein said tampering is by crushing 37. The oral dosage form of claim 27 wherein said tampering is m a manner as to obtain an immediate release of said agonist 38. The oral dosage form of claims 1-9 wherein said tampering is to make the agonist available for mappropnate use. 39. The oral dosage form of claims 1-9 wherein said antagonist does not significantly affect analgesia provided by the agonist. 40. A method of decreasing the abuse of an opioid agonist in an oral dosage form, comprising mcoφoratmg said opioid agonist into a dosage form of clarms 1-9 41. A dosage form compnsing: (a) an opioid agonist; and (b) naltrexone in a substantially non-releasable form, wherein the agonist and naltrexone are at least partially interdispersed. 42. The dosage form of claim 41 wherein the opioid agonist is oxycodone, codeine, hydrocodone, hydromoφhone, levoφhanol, meperidme, methadone, moφhme, salts thereof, or mixtures thereof 43. The dosage form of claim 42 wherein the opioid agonist is oxycodone hydrochlonde 44 The dosage form of claim 42 wherein the opioid agonist is hydrocodone bitartrate β3 45. The dosage form of claim 42 wherein the opioid agonist is hydromoφhone hydrochloride. 46. The dosage form of claim 41 wherein at least part of the naltrexone is in a matrix. 47. The dosage form of claim 41 wherein at least part ofthe naltrexone is in a coated bead. 48. The dosage form of claim 41 wherein the naltrexone in a substantially non-releasable form is adapted to release less than 15% by weight of the naltrexone in \ ivo after 36 hours. 49. The dosage form of claim 48 wherein the naltrexone in a substantially non-releasable form is adapted to release less than 8%> by weight of the naltrexone in o after 36 hours. 50. The dosage form of claim 49 wherein the naltrexone in a substantially non-releasable form is adapted to release less than 1% by weight ofthe naltrexone in vivo after 36 hours. 51. The dosage form of claim 41 wherein the naltrexone in a substantially non-releasable form is adapted to release less than 3%> by weight ofthe naltrexone in vivo after 1 hour. 52. The dosage form of claim 41 wherein the naltrexone in a substantially non-releasable form is adapted to release less than 1.0% by weight ofthe naltrexone in vivo after 1 hour. 53. The dosage form of claim 41 wherein the naltrexone in a substantially non-releasable form is adapted to release less than 0.5% by weight of the naltrexone in vivo after 1 hour. 54. A dosage form comprising: (a) an opioid agonist, and (b) an orally-bioavailable opioid antagonist m a substantially non-ieleasable fonn The dosage foπn of claim 54 wherein the agonist and antagonist are at least partially interdispersed The dosage form of claim 54 wherein the orally-bioavailable opioid antagonist is naltrexone, or a salt thereof The dosage form of claim 54 wherein the opioid agonist is oxycodone, codeine, hydrocodone, hydromoφhone, levoφhanol, mependme, methadone, moφhme, or salts thereof or mixtures thereof The dosage form of clarm 54 wherern at least part of the antagonist is m a matrix The dosage form of claim 54 wherein at least part of the antagonist is m a coated bead A method of preparing an oral dosage form comprising pretreatmg an opioid antagonist to render it substantially non-releasable, and combining the pretreated antagonist with a releasable form of an opioid agonist A method of treating pain compnsing admmistenng to a human patient a dosage fonn of claims 1-9, 41 or 54 §b

Inventors: OSHLACK BENJAMIN, WRIGHT CURTIS, OSHLACK, BENJAMIN, WRIGHT, CURTIS
Applicants: EURO CELTIQUE SA, OSHLACK BENJAMIN, WRIGHT CURTIS, EURO-CELTIQUE, S.A., OSHLACK, BENJAMIN, WRIGHT, CURTIS
Application year: 2001
Main classification: A61K31
IPC codes: A61K9, A61K31, A61K38, A61K45, A61K47, A61P25, A61P39, A61P43