Opioid switch to oral methadone in cancer pain.

The occurrence of undesirable side effects due to opioids (delirium, confusion, myoclonus, nausea, emesis) is one of the major complications in the management of pain, especially in chronic cancer pain states. Methadone, as an alternative to morphine, has been proposed in the control of opioid-induced toxicity. Methadone is a synthetic opioid, with mu and delta receptor activity, associated with the capacity to inhibit N-methyl-D-aspartate receptors. Questions have arisen concerning its equianalgesic ratio since its rediscovery over the past few years and are certainly related to its receptor interactions. Aspects of its pharmacology, indications, and switching modalities are discussed here. Opioid rotation is a new tool in the management of cancer pain, deserving more attention.