The veterinary experience

Veterinarians have three decades of experience with the use of α2-agonists. Xylazine, synthesized in 1962, was the first α2-agonist to be used as a sedative and analgesic, first in cattle and later in many other species. The major side-effects were bradycardia and a biphasic blood pressure response with moderate hypotension following an initial hypertensive episode. In the 1980s, new α2-agonists with a much higher potency and greater specificity at central α2-adrenoceptor sites were introduced: detomidine, romifidine and medetomidine. These drugs showed side-effects similar to those of xylazine but had a longer sedative and analgesic action. Alpha2-agonists have proved to be safe agents for analgo-sedation and muscle relaxation in healthy animals. In combination with opioids or mono-anaesthetics, they can be used either to induce a profound sedative-analgesic state or to enhance general anaesthesia while reducing the anaesthetic requirement and smoothing the recovery phase. The availability of α2-antagonists such as atipamezole has increased safety and allowed remarkable versatility in veterinary anaesthetic management.