In contrast to morphine, tramadol has not been shown to cause histamine release. Analgesia in humans begins approximately within one hour after administration and reaches a peak in approximately 2 to 3 hours.Īpart from analgesia, tramadol hydrochloride administration may produce a constellation of symptoms (including dizziness, somnolence, nausea, constipation, sweating and pruritus) similar to that of other opioids. These mechanisms may contribute independently to the overall analgesic profile of tramadol hydrochloride. Tramadol has been shown to inhibit reuptake of norepinephrine and serotonin in vitro, as have some other opioid analgesics. The relative contribution of both tramadol and M1 to human analgesia is dependent upon the plasma concentrations of each compound (see CLINICAL PHARMACOLOGY: Pharmacokinetics). Tramadol-induced analgesia is only partially antagonized by the opiate antagonist naloxone in several animal tests. In animal models, M1 is up to 6 times more potent than tramadol in producing analgesia and 200 times more potent in µ-opioid binding. Opioid activity is due to both low affinity binding of the parent compound and higher affinity binding of the O-demethylated metabolite M1 to µ-opioid receptors. Although its mode of action is not completely understood, from animal tests, at least two complementary mechanisms appear applicable: binding of parent and M1 metabolite to µ-opioid receptors and weak inhibition of reuptake of norepinephrine and serotonin. Tramadol is a centrally acting synthetic opioid analgesic.
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