Tramadol (Molecule of the Month for April 2008)
Tramadol is an atypical opioid which is a centrally acting analgesic, used for treating moderate to severe pain. It is a synthetic agent, as a 4-phenyl-piperidine analogue of codeine, and appears to have actions on the GABAergic, noradrenergic and serotonergic systems. Tramadol was developed by the German pharmaceutical company Grünenthal GmbH in the last years of 1970s and marketed under the trade name Tramal. Tramadol is usually marketed as the hydrochloride salt (tramadol hydrochloride) and is available in both injectable (intravenous and/or intramuscular) and oral preparations. It is also available in conjunction with paracetamol (acetaminophen). Tramadol is marketed as a racemic mixture with a weak affinity for the μ-opioid receptor (approximately 1/6th that of morphine). 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).
Tramadol is not considered a controlled substance in many countries (the U.S. and Australia, among others), and is available with a normal prescription. Tramadol is also available over-the-counter without prescription in a few countries. Some controversy exists regarding the dependence liability of tramadol. Grünenthal has promoted it as an opioid with a lower risk of opioid dependence than that of traditional opioids, claiming little evidence of such dependence in clinical trials.
Tramadol for animals is one of the most reliable and useful active principles available to veterinarians for treating animals in pain. It has a dual mode of action: mu agonism and monoamine reuptake inhibition, which produces mild anti-anxiety results. Tramadol may be utilized for relieving pain in cats and dogs. This is an advantage because the use of some non-steroidal anti-inflammatory substances in these animals may be dangerous.
Formal Chemical Name (IUPAC)
Update by Karl Harrison
(Molecule of the Month for April 2008 )