Role of methadone in the management of pain in cancer patients.

In most cancer patients who are treated with opioid analgesics for pain control, the type of opioid needs to be changed at least once because of the presence of side effects or the need to escalate analgesic doses to toxic levels. Methadone may be an excellent alternative in such patients due to its lack of known active metabolites, high lipid solubility, excellent absorption following oral and rectal delivery, and extremely low cost. However, it has unique problems, such as a long, unpredictable half-life and greater potency than previously assumed. At present, methadone is viewed as a second-line opioid for chronic cancer pain. Better pharmacokinetic and clinical studies are required to establish the role of methadone in this setting. Issues to be explored include a potential role in treating patients who have poorly responsive pain syndromes, such as neuropathic pain, or who develop a rapid tolerance to other opioids; the possibility of extending dosing intervals to every 12 or 24 hours; and its possible use as a first-line opioid.