Heroin, is “an illegal opiate drug exerts its addictive effect by activating brain regions responsible for producing both the pleasurable sensation of reward and physical dependence”. The direct effects of the opioids on the CNS include sedation by suppressing the reticular-activating system in the brainstem; nausea and vomiting by activating the chemo-trigger zone in the medulla; reduced pain reception by suppressing the spinal cord, thalamus, and periaqueductal gray region in the midbrain; and euphoria by stimulating the limbic system.
In addition, acute and chronic administration of opioids produce decrease in luteinizing hormone, testosterone, and cortisol, resulting to diminished libido, amenorrhea, impotence and inorgasmia, and reduced sperm count. Approximately 0.4% of the global population aged between 15 and 64 years old are heroin users. Different treatment regimens have been used and one of this is the methadone-maintenance therapy (Rettig & Yarmolinsky, 1995).
Methadone is a synthetic opioid used primarily as an anti-addictive drug by patients dependent on opiates such as heroin and as analgesia for chronic severe pain due to its long duration of action and very low cost. It binds to the mu-opioid receptor, acts as a receptor antagonist against glutamate (primary excitatory neurotransmitter in the CNS) and is metabolized by enzyme CYP3A4 and CYP2D6. Its adverse effects are respiratory depression, decreased bowel motility, miotic pupils, nausea and hypotension. Naloxone is the antidote for methadone toxicity. Methadone is prescribed as maintenance therapy for patients addicted to heroin because of its long half-life that delays the abstinence syndrome and its blockage for heroin’s euphoric effect.
Methadone decreases cravings for opioids by acting as an NMDA (N-methyl-D-aspartate) antagonist. Moreover, it decreases the incidence of infectious disease among heroin addicts. Methadone maintenance therapy starts at 10 to 20 mg of methadone, increasing in 10-mg increments until withdrawal symptoms are controlled under careful supervision. Methadone is effective for pain management, a good alternative to morphine sulfate. Its route of administration is in a racemic oral solution available in the form of pill, sublingual tablet and liquid formulations. It is also available in form of injection used under strict supervision but is often times abused therefore oral administration is more advisable (Sadovsky, 2000).
Some survey studies provide valuable information about the use of methadone in community-based treatment clinics. Overall, results from survey studies produced two conclusions: methadone treatment is effective and second, higher methadone doses are more effective than lower doses. A fundamental public health issue related to methadone maintenance was whether or not a methadone-maintained patient would be in jeopardy of overdose of a person self-administered heroin during methadone treatment. In 1964, a cross-tolerance studies documented that the risk of morbidity or death in methadone patients receiving a full treatment dose (60 to 120 mg per day) is extremely low because of the high level of tolerance (and cross tolerance to other opiates) developed during treatment.
In addition to blocking the euphoric effects of superimposed, short-acting opiate drugs, methadone and its accompanying narcotic “blockade” may serve a relapse-prevention function. The suppression and ultimate “extinction” of drug-seeking behavior should result, theoretically at least, when elicit opiate self-administration is uncoupled from the anticipated and desired opiate effect of euphoria.
The now well documented significant reduction or cessation of illicit opiate use by former heroin addicts stabilized on steady and adequate doses of methadone suggests that this may be due partly to the effects of counseling, as well as the direct biological effects of the drug (Rettig & Yarmolinsky, 1995). The major achievement of the methadone treatment program is the dramatic reduction in the arrest rates of the addict patients. Since drug addiction has been associated to AIDS and hepatitis, this treatment is also been incorporated in HIV treatment program. Methadone-associated mortality, however, has been attributed to overdoses (Rettig & Yarmolinsky, 1995).
Rettig, R. A., & Yarmolinsky, A. (1995). Federal Regulation of Methadone Treatment: National Academies Press.
Sadovsky, R. (2000). Public Health Issue: Methadone Maintenance Therapy [Electronic Version]. American Academy of Family Physicians News & Publications, 62. Retrieved February 24, 2008, from http://www.aafp.org/afp/20000715/tips/1.html