Agonistantagonist Mixed A

mixed agonist-antagonist is a drug or receptor li-gand that possesses pharmacological properties similar to both AGONISTS and ANTAGONISTS for certain RECEPTOR sites. Well-known mixed agonist-antagonists are drugs that interact with OPIOID (morphine-like) receptors. Pentazocine, nalbuphine, butorphanol, and BUPRENORPHINE are all mixed agonist-antagonists for opioid receptors. These drugs bind to the ¡i (mu) opioid receptor to compete with other substances (e.g., MORPHINE) for this binding site; they either block the binding of other drugs to the ¡i receptor (i.e., competitive antagonists) or produce a much smaller effect than that of "full" agonists (i.e., they are only partial agonists). Therefore, these drugs block the effects of high doses of morphine-like drugs at ¡i opioid receptors, while producing partial agonist effects at k (kappa) and/or 8 (delta) opioid receptors. Some of the mixed opioid agonist-antagonists likely produce analgesia (pain reduction) and other morphine-like effects in the CENTRAL NERVOUS SYSTEM by binding as agonists to k opioid receptors.

In many cases, however, there is an upper limit (ceiling) to some of the central nervous system effects of these drugs (e.g., respiratory depression). Furthermore, in people physically addicted to morphine-like drugs, the administration of a mixed opioid agonist-antagonist can produce an abstinence (WITHDRAWAL) syndrome by blocking the ^ opioid receptor and preventing the effects of any ^ agonists (i.e., morphine) that may be in the body. Pretreatment with these drugs can also reduce or prevent the euphoria (high) associated with subsequent morphine use, since the ¡i opioid receptors are competitively antagonized. Therefore, the mixed opioid agonist-antagonists are believed to have less ABUSE LIABILITY than full or partial opioid receptor agonists.

As more and more subtypes of receptors are discovered in other NEUROTRANSMITTER systems

(there are now more than five serotonin receptor subtypes and five dopamine receptor subtypes), it is quite likely that mixed agonist-antagonist drugs will be identified that act on these receptors as well.


Gilman, A. G., et al. (Eds.). (1990). Goodman and Gilman's the pharmacological basis of therapeutics, 8th ed. New York: Pergamon.

NickE. Goeders

AIDS See Alcohol and AIDS; Complications: Route of Administration; Injecting Drug Users and HIV; Substance Abuse and AIDS; Needle and Syringe Exchanges and HIV/AIDS

AL-ANON Al-Anon is a fellowship very similar to Alcoholics Anonymous (AA), but it is for family members and friends of alcoholics. Although formally totally separate from the fellowship of AA, it has incorporated into its groups the AA Twelve Steps and Twelve Traditions and AA's beliefs and organizational philosophy, but it has directed them toward helping families of alcoholics cope with the baffling and disturbing experiences of living in close interaction with an active alcoholic. In this sense, it is a satellite organization of AA (Rudy, 1986). Proselytizing organizations, such as AA, of necessity attempt to reduce, even eliminate, the ties of newcomers with other significant persons and groups who are not members. Rather than attempt to sever those bonds for prospective AA members, AA evolved Al-Anon as a way to include families into a parallel organization, and thus also initiate them into the beliefs and practices of AA. In addition, as AA expanded and more alcoholics became "recovering" ones, close relatives became aware that their own personal problems could be reduced by applying AA principles to themselves and working the Twelve Step program, even though they were not alcoholic. In 1980, there were 16,500 Al-Anon groups worldwide, including 2,300 ALATEEN groups of children of alcoholics (Maxwell,

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