Richard C. Dart, MD, PhD; George E. Woody, MD; Herbert D. Kleber, MD
Potential Financial Conflicts of Interest: Dr. Dart administers Denver Health's contract with Purdue Pharma to provide poison center surveillance data on the misuse and abuse of prescription drugs. He receives no additional direct or indirect remuneration for this work as an employee of Denver Health. Dr. Kleber is a consultant for Purdue Pharma and Abbott.
Dart R., Woody G., Kleber H.; Prescribing Methadone as an Analgesic. Ann Intern Med. 2005;143:620. doi: 10.7326/0003-4819-143-8-200510180-00028
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Published: Ann Intern Med. 2005;143(8):620.
TO THE EDITOR:
Internists are often involved in the care of patients with chronic pain. Increased awareness of the need for adequate pain relief, combined with concerns about the costs and the potential abuse of extended-release formulations of opioid analgesics, has led to markedly increased use of methadone as an analgesic. Methadone tablets, in contrast to the liquid formulation used for substance abuse, are primarily used to treat pain. Methadone tablet prescriptions in the United States increased from 437 030 in 2001 to 2 609 613 in 2004, while prescriptions of hydrocodone and oxycodone increased only slightly (1). Methadone's slow onset, its ability to suppress withdrawal for over 24 hours, and its low cost make it an appropriate choice for maintenance addiction treatment. In contrast, its pharmacologic properties require that clinicians prescribing it for analgesia be fully aware of other important characteristics. Methadone's analgesic effect is 4 to 6 hours, similar to that of morphine (2, 3). In contrast, its elimination half-life averages 24 to 36 hours and can range from 15 to 40 hours or more (2, 3). Since the duration of methadone's analgesic effect is much shorter than its elimination half-life, a potentially dangerous trap is created. If the initial dose is increased too rapidly or administered too frequently to improve pain relief, the resulting accumulation of methadone may cause respiratory depression and even death. A Cochrane review of methadone as an analgesic noted, “There is a very significant danger that the effects of methadone accumulation leading to delayed onset of adverse effects which occurs with chronic administration has not been represented” (4). When methadone is used as an analgesic, therefore, the dose should be titrated to effect very slowly while carefully monitoring patient response to avoid overmedication.
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