Ultram

Tramadol is a centrally acting analgesic, used for treating moderate to severe pain. It is a synthetic opioid and it appears to have actions at the μ-opioid receptor as well as the noradrenergic and serotonergic systems. Tramadol was developed by the German pharmaceutical company Grünenthal GmbH in the late 1970s and marketed under the trade name Tramal.

The mode of action of tramadol has yet to be fully understood, but it is believed to work through modulation of the noradrenergic and serotonergic systems in addition to its mild agonism of the μ-opioid receptor. The contribution of non-opioid activity is demonstrated by the fact that the analgesic effects of tramadol is not fully antagonised by the μ-opioid receptor antagonist naloxone.

Tramadol is marketed as a racemic mixture with a weak affinity for the μ-opioid receptor (approximately 1/6000th that of morphine; Gutstein & Akil, 2006). The (+)-enantiomer is approximately four times more potent than the (-)-enantiomer in terms of μ-opioid receptor affinity and 5-HT reuptake, whereas the (-)-enantiomer is responsible for noradrenaline reuptake effects (Shipton, 2000). These actions appear to produce a synergistic analgesic effect, with (+)-tramadol exhibiting 10-fold higher analgesic activity than (-)-tramadol (Goeringer et al., 1997).

The serotonergic-modulating properties of tramadol give tramadol the potential to interact with other serotonergic agents. There is an increased risk of serotonin syndrome when tramadol is taken in combination with serotonin reuptake inhibitors (e.g., SSRIs) or with use of a light box, since these agents not only potentiate the effect of 5-HT but also inhibit tramadol metabolism. Tramadol is also thought to have some NMDA-type antagonist effects, which has given it a potential application in neuropathic pain states.