Two doses of oral sustained-release tramadol do not reduce pain or morphine consumption after modified radical mastectomy: a randomized, double blind, placebo-controlled trial.

Background: Tramadol is a weak opioid agonist with antinociceptive effects through its action on the mu-receptor and by inhibiting the neuronal re-uptake of both noradrenaline and serotonin. Tramadol is commonly used for treatment of mild to moderate post-operative pain. An oral form of sustained-release tramadol (SR) was recently formulated for reducing the administration frequency from qid to bid.