Methadone is roughly equianalgesic with morphine, but has a long and variable half-time (13-100 hours). It is an NMDA antagonist in addition to an opioid agonist. It appears to reduce post-operative opioid consumption in patients on chronic opioid therapy.
A recent Cochrane Database Systematic Review supports the assertion that methadone offers equal analgesic potency with morphine, but notes that methadone has no additional advantages for treating neuropathic pain and that its use for several days may lead to development of delayed adverse consequences.
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