Analgesic effect of adrenergic agonists,Efecto analgésico de los agonistas α<inf>2</inf>-adrenérgicos

At present, α2-adrenergic agonists have been shown to produce effective analgesia in different types of acute and chronic pain. Their effects are mediated by specific membrane receptors located at spinal, supraspinal and peripheral sites, in close association with nervous structures that participate in nociceptive transmission. In man, clonidine as a sole analgesic, has been proven to be effective in the treatment of acute pain of moderate to severe intensity and in certain types of chronic pain, mainly those with a sympathetic component. Clonidine is effective by all routes of administration and the analgesic effect is frequently accompanied by side effects such as sedation, hypotension/bradicardia and inhibition of gastrointestinal transit. At present, the use of α2-adrenergic agonists as sole analgesics is limited, due to the availability of more potent and efficacious analgesic drugs. However, their ability to enhance the analgesia induced by local anesthetics, opioids and cholinergic drugs (among others), permits a reduction the dose/s of the individual agents, and consequently a decrease in the incidence and severity of side effects. Thus it is likely that clonidine and other α2-adrenergic agonists, will play an essential role in the techniques of balanced or «multimodal» analgesia, used in the treatment of acute and chronic pain in humans.