Opioid Agonist Pharmacotherapy
Methadone maintenance has become the most commonly used pharmacotherapy for opioid dependence. Methadone acts at the μ-opioid receptor and its ability to suppress opioid with-drawal for 24 to 36 hours following a single oral dose makes it an ideal medication for this purpose. Another μ-opioid agonist, LAAM, received FDA approval for maintenance treatment in 1993. LAAM is a long-acting congener of methadone that sup-presses withdrawal for 48 to 72 hours and thus has the advan-tage of requiring less frequent clinic visits than methadone, which must be taken daily. A third medication, buprenorphine, has received FDA approval. It has been mentioned above as a detoxification agent and will be discussed later and in more detail as it has unique properties that are likely to result in it being used with fewer regulatory controls than methadone and LAAM.
Both methadone and LAAM are Schedule II controlled substances and can only be used for maintenance and detoxifica-tion in programs that are licensed and regulated by the FDA and the Drug Enforcement Administration (DEA). The regulations specify who is eligible for treatment, procedures that are required for its administration, the number of take-home doses permitted, and the type of medication storage security needed. Treatment programs have been inspected approximately every 3 years for the past 30 years and violations have resulted in sanctions rang-ing from administrative citations to criminal prosecution.
A combination of regulations has resulted in a treatment system that is separated from the mainstream of other medical care and that consists almost entirely of specially licensed and inspected clinics. Clinics are often located in old buildings that have been converted to comply with regulations but that were never intended for medical use. At the present time, it is esti-mated that approximately 179 000 patients are being maintained on methadone or LAAM at 940 or more sites, and that this number represents only about 20% of all persons with opioid dependence in the USA (Addiction Treatment Forum, 2000). This situation is very unlike that of some other western countries such as Spain and Switzerland where 50% or more of persons with opioid de-pendence are reported to be on agonist therapy, with substantial numbers of others in residential treatment.
The appropriate dose of agonist medication has been a sub-ject of both federal and state regulations, although there has been a gradual shift toward allowing more clinical judgment in its de-termination. A number of studies have been done during the last 25 years to determine the optimal dose and, although it is clear that some patients do well on low doses of methadone or LAAM (about 20–50 mg), studies have consistently shown that most individuals need higher doses if they are to achieve maximum benefit from agonist treatment. The results of these comparison studies are generally supportive of the guidelines originally pro-posed by Dole and Nyswander, who recommended doses in the 80 to 120 mg/day range (Dole and Nyswander, 1968)
Physicians who choose to treat persons with opioid de-pendence under new regulations will need to notify the Secretary of Health and Human Services in writing of their intent and show that they are qualified to provide addiction treatment by virtue of certification or experience. No physician will be allowed to treat more than 30 patients at one time without special approval according to the proposed legislation. This change in the regu-lations will be especially important for buprenorphine and the buprenorphine/naloxone combination as it will provide better access to treatment for persons who are unwilling or unable to be treated in the current methadone or LAAM system. The over-all intent of the proposed regulatory reform is better to integrate maintenance treatment into the mainstream of medical care, and to make it more available and improve its quality. These changes are likely to influence the ways that buprenorphine is used in opioid addiction treatment.
The greatest advantage of buprenorphine compared with full agonists such as methadone and LAAM is the plateau effect of μ-agonist activity. A number of large trials have confirmed the utility of buprenorphine for agonist maintenance therapy. Buprenorphine has the potential to be abused and can produce addiction; however, most persons who abuse buprenorphine initiated opioid use with other drugs.
Buprenorphine, in combination with naloxone, has less potential for abuse than buprenorphine alone. The therapeutic utility of combining naloxone with buprenorphine derives from the low sublingual bioavailability of naloxone as compared with buprenorphine. Parenteral misuse of the combination by persons addicted to opioids would be expected to produce an-tagonist like effects; thus, most persons with opioid dependence would be unlikely to inject the combination more than once. The use of the buprenorphine/naloxone combination in an of-fice-based setting represents an innovative alternative to the restrictive methadone or LAAM maintenance paradigm and should expand the availability of agonist maintenance treatment with a relatively low risk for abuse or diversion. In addition, the partial agonist activity of buprenorphine results in a much lower risk for overdose death than is the case with methadone or LAAM.