“Approximately 80 percent of cancer patients require one switch in an analgesic drug regimen, up to 44 percent require trials of two or more systemically administered opioids, and 20 percent require sequential trials of three or more opioids.” Enck RE: Switching to methadone. American Journal of Hospice & Palliative Care. 16(3): 149-150.
2.
Morley J, Makin M: The use of methadone in cancer pain poorly responsive to other opioids. Pain Reviews. 1998; 5: 51-58.
3.
Twycross R, Wilcock A: Symptom Management in Advanced Cancer. 3rd Ed.Abingdon, Oxon, UK: Radcliffe Medical Press: 382-383.