CLINICAL EFFICACY OF METHADONE IN PATIENTS REFRACTORY TO OTHER MU-OPIOID RECEPTOR AGONIST ANALGESICS FOR MANAGEMENT OF TERMINAL CANCER PAIN- CASE PRESENTATIONS AND DISCUSSION OF INCOMPLETE CROSS-TOLERANCE AMONG OPIOID AGONIST ANALGESICS

Background. Development of tolerance to opioid analgesics occurs often in patients with cancer-related pain. Cross-tolerance among opioid an algesics provides the physician with a major management problem. Incom plete cross-tolerance among opioid analgesics has been demonstrated to occur in animals and humans. The current study provides clinical evid ence of the incomplete cross-tolerance of methadone with a number of m u-opioid agonist analgesics in patients with advanced cancer-related p ain. Results. Patients presented in the current study had cancer-relat ed pain refractory to other mu-opioid receptor agonist analgesics as e videnced by inadequate analgesia despite escalation of opioid dose. Al l patients were adequately managed by conversion of their opioid dose to methadone. Additionally, the dose of methadone required to establis h and maintain analgesia in these patients was modest compared with pr evious opioid dose requirements. Conclusions. Methadone is a potent op ioid analgesic that demonstrates incomplete cross-tolerance with other mu-opioid receptor agonist analgesics. Conversion of the opioid-toler ant patient with cancer-related pain to methadone may represent an imp ortant therapeutic option in the management of patients with this diff icult problem.