Rationale: Experimental data demonstrates a profound analgesic synergy between morphine and methadone when co-administered systemically in mice. If this type of synergy can be demonstrated in clinical pain, it will be a relatively unique example of translating concepts of fundamental aspects of opioid actions seen in the laboratory to the clinical area, and provide a basis for offering new and scientifically- based analgesic regimens. This may provide better pain relief with less opioid related side effects in clinical practice.~Purpose:~This is a randomized, double blind, parallel arm Phase II study comparing a single dose of 1:1 combination of methadone and morphine with morphine alone in patients with post-operative pain.~The primary objective of this randomized, double blind, parallel arm Phase II study is to compare the analgesic effects of a combination of morphine and methadone with morphine alone to determine synergistic activity of mu opioid analgesics in patients with post-operative pain.~A second goal is to further evaluate any side effects of the combination of morphine and methadone.
This is a randomized Phase II study testing the effectiveness of the combination of morphine and methadone versus morphine alone in relieving pain. A second goal is to further evaluate any side effects of the combination of morphine and methadone.