Med. Weter. 68 (11), 643-646, 2012

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Giorgi M.
Tramadol and tapentadol hydrochloride: an old and a novel atypical opioid drug. An overview on their present and potential applications
Acute and chronic pain is a common presenting condition in both animal species and human beings. Classical opioids provide very effective pain relief, although they may be less effective in the treatment of chronic pain due to their limited therapeutic windows and the induced opioid receptor down regulation. Atypical opioids, such as tramadol and tapentadol, have a dual mechanism of action and have been designed to overcome these issues through an opiate-sparing effect. Tramadol activates mu opioid receptors and in addition, inhibits serotonin and noradrenalin reuptake. These actions are the result of the different enantiomers and tend to be reliant on their metabolism. Indeed, the O-desmethyltramadol phase I metabolite, is 200-300 times more potent for mu opioid receptor activation than the parental compound. For these reasons, the drug’s effectiveness can vary among subjects. In veterinary medicine its effectiveness, especially after oral administration, is still uncertain and controversial. Tapentadol is a novel, atypical opioid with a unique mechanism of action. It was launched on the European drug market at the end of 2011. It has been proposed as the first representative of a new pharmacological class of centrally acting analgesics, namely, the mu opioid receptor agonist, noradrenalin reuptake inhibitors. The first human studies describe this molecule as safe and effective (equianalgesic to morphine). The drug has great potential for veterinary use because it exists as a single enantiomer only, it does not require metabolic activation to be effective and adverse effects triggered by the serotonin reuptake inhibition action are negligible. For these reasons, TAP is a promising compound however at this stage, more investigation is required before it can be recommended for regular use in veterinary medicine, the possibility of undesirable effects is yet to be entirely excluded.
Key words: mu receptor, Veterinary species, Opioid, Noradrenaline reuptake, Pain