Differences in the ratios of morphine to methadone in patients with neuropathic pain versus non-neuropathic pain

The use of methadone in the treatment of cancer pain is becoming more attra ctive mainly because of its known efficacy, lack of active metabolites, and low cost. Methadone also blocks the n-methyl-D-aspartate (NMDA) receptor; and this property may result in other clinical advantages. Bemuse of this c apacity of methadone to block the NMDA receptors, we have hypothesized that the equianalgesic dose ratio of hydromorphone or morphine to methadone wil l be different in patients with neuropathic pain than in patients with non- neuropathic pain. To explore this hypothesis, we reviewed computerized pati ent records and determined the ratio of morphine and hydromorphone (express ed as morphine subcutaneous equivalent dose) to methadone in patients who u nderwent rotation from morphine or hydromorphone to methadone. We found tha t the ratio of morphine subcutaneous equivalent dose to methadone is betwee n 5 and 7, which is different from previously described dose ratios. Howeve r, our study failed to show a difference in the ratios of patients with neu ropathic or non-neuropathic pain syndromes. (C) U.S. Cancer Pain Relief Com mittee, 1999.