Morphine to methadone conversion: an interpretation of published data.

For the past 20 years, methadone has been experiencing resurgence in the palliative care community as a second-line opioid for the treatment of cancer pain. The advantages of using methadone for refractory pain in patients with cancer or in those who could not tolerate the side effects of other opioids such as morphine are well cited in recent literature. Advantages of methadone over other opioids include dual elimination without active metabolites, allowing safe use with renal and liver failure, N-methyl-D-aspartate (NMDA) and delta receptor activity in addition to mu receptor agonism, multiple routes of administration, rapid onset of action, long half-life, low cost, and fewer adverse effects. Despite the abundance of recent case reports and literature reviews demonstrating the effective use of methadone in patients with cancer, there is a lack of consensus for an appropriate method for converting morphine (and by extension, other opioids) to methadone. This article will review methadone pharmacology and multiple proposed conversion methods; a case report illustrating a popular method for high-dose conversion is also included.