Thursday, April 9, 2009

The Perils of Polydrug Abuse

Methadone and benzodiazepines.

For patients in opiate treatment programs, benzodiazepine use represents both a barrier to recovery and a potentially life threatening situation. The combination of benzodiazepines and methadone can lead to fatal overdose.

The five most commonly prescribed benzodiazepines fall into two major categories. High potency medications include Xanax (Alprazolam), with a short half-life of six to 12 hours, and Ativan (Lorazepam), with a slightly longer half-life. The low-potency benzodiazepines are represented by the short-lived Restoril (Temazepam), and the longer-lasting Valium (Diazepam), with a half-life of 20 to 100 hours. The fifth popular benzodiazepine, Klonopin (Clonazepam) is a high-potency drug with a half-life of 18 to 50, the highest in its class. Their primary clinical uses include the treatment of anxiety disorders, insomnia, convulsions, and muscle spasms. They also find use in the treatment of acute mania, catatonia, and detoxification from alcohol.

While some patients are able to use benzodiazepines safely at low dosage for years, patients with a history of opiate addiction are a high-risk category for these medications. Tolerance develops quickly in patients who use benzodiazepines to “boost” the effect of methadone, or as a sedative during opioid withdrawal. Since high doses of benzodiazepines cause respiratory depression, even among opioid users who have developed a high tolerance to such effects, the combination increases the risk of severe intoxication, injuries, or fatal overdose.

In addition, benzodiazepines and methadone interact pharmacologically through the actions of the CYP450 liver enzyme, which detoxifies both substances. If the work load for CYP450 becomes too great, the result can be an accumulation of high levels of methadone in the body.

It has been estimated that “80 percent of benzodiazepine abuse is part of polydrug abuse, most commonly with opioids.” In a two-year study by the National Institute of Drug Abuse (NIDA), 73 per cent of heroin users also used benzodiazepines more often than weekly.

According to a recent Canadian study of 172 subjects, the reported lifetime prevalence of benzodiazepine abuse in methadone maintenance patients ranged from 67 to 94 percent, with two-thirds of the patients reporting benzodiazepine use during the past 6 months. Patients who took benzodiazepines also reported more previous opioid overdoses, according to the study. And women are more likely than men to abuse benzodiazepines. In a study by Australia’s National Drug and Alcohol Research Centre (NDARC), researchers conducting a five-year study of heroin overdoses in New South Wales found that attempted suicide by benzodiazepine overdose was more common than attempted suicide by heroin overdose.

Methadone maintenance patients need to be questioned carefully about benzodiazepine use. By doing so, physicians and other caregivers can work toward actively decreasing the likelihood of treatment failure or fatal methadone overdose.

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