The association of clonidine with an opioid is a major step toward th "ideal opioid" analgesia. : an analysis of the antinociceptive properties of the alpha 2-adrenoceptor agonists when confronted with acute postoperative pain

Is there an intrinsic antinociceptive effect to explain the analgesic benefits afforded by the α2-adrenoceptor agonists against acute somatic pain ? Form laboratory experimentation, the exercise of an original analgesic effect (or at least an effect totally independent of the opiates) is not demonstrated beyond doubt. Moreover, some experimental evidence indicates the existence of close relationships between the α2-adrenergic and the opiate systems for analgesia. Human studies d not prove that α2-adrenoceptor agonists, given alone, have such an intrinsic analgesic effect which would allow to substitute them for opioids. Both experimental and human evidence indicates the narrow tangling between sedative and antinociceptive properties of the α2-adrenoceptor agonists particularly when using large doses. These observations, however, do not exclude that α2-adrenergic agonists may possess some specific analgesic properties against particular pain stimuli such as visceral (81), neuropathic (154, 334, 352) or sympathetically-mediated pain (82). Concerning the site of the antinociceptive action, α2-adrenoceptors located at the spinal dorsal horn undoubtedly play a critical role but α2-adrenergid agonists may have multiple possible mechanisms of action (i.e. local anesthetic effect), depending on the concentration and the site of applicationThèse d'agrégation de l'enseignement supérieur -- UCL, 199