Methadone in the management of intractable neuropathic noncancer pain

OBJECTIVE: To evaluate the role of methadone in the management of intractable neuropathic noncancer pain. METHODS: A case series of 50 consecutive noncancer pain patients who were seen at a tertiary care centre and treated with oral methadone for a variety of intractable neuropathic pain states. RESULTS: The mean age was 52.7 years and the mean duration of follow-up was 13.9 months. Post-discectomy nerve root fibrosis, complex regional pain syndrome, peripheral neuropathy and central spinal cord pain syndromes were the most common diagnoses. Over 90% had been treated with one or more tricyclic antidepressants and anticonvulsants and a similar number had received other adjuvant analgesics. All patients had failed treatment with one or more conventional opioid analgesics (mean 2.8) at a mean maximal morphine dose of 384 mg (or equivalents) per day. Twelve patients had failed spinal cord stimulation. Nineteen patients (38%) did not tolerate initial methadone titration or thought their pain was worse on methadone. Five patients (10%) declared initial benefit but required repetitive dose escalation and eventually became non-responders. Twenty-six patients (52%) reported mild (4), moderate (15), marked (6) or complete (1) pain relief and continued on methadone at a mean maintenance dose of 159.8 mg/day for a mean duration of 21.3 months. Fourteen patients (28%) reported improved function on methadone relative to previous treatments. CONCLUSIONS: Methadone appears to have unique properties including N-methyl-D-aspartate antagonist activity that may make it especially useful in the management of intractable neuropathic pain. This observation needs to be tested in randomized, controlled trials.