[The role of clonidine in anesthesia]

For decades the adrenergic alpha2 agonist clonidine has been considered to be one of the classical, centrally acting antihypertensive agents. In addition to its antihypertensive and sympathicolytic effects, in recent studies clonidine has been demonstrated to be an effective sedative and analgesic and to reduce the amount of anaesthetic agents required. Therefore, a reconsideration of possible new indications for clonidine in clinical anaesthesiology seems to be justified. This paper presents the pharmacological basis for treatment with clonidine and reviews the extensive literature on its clinical indications in anaesthesia. Clonidine apparently produces its sedative and anaesthetic-sparing effects by stimulation of centrally located alpha2 adrenoceptors. Analgesia seems to be mediated mainly by activation of alpha2 adrenoceptors in the dorsal horn of the spinal cord. Considering its clinical indications, clonidine is often used as a supplement in the treatment of alcohol withdrawal syndromes. Future indications for clonidine may be the treatment of postoperative shivering and chronic pain management. Administration of clonidine in combination with a local anaesthetic prolongs analgesia and motor blockade. Its use in premedication and postoperative pain management may be limited by its principal effects of hypotension and bradycardia. In future, cardiovascular side effects may be minimized if all the subtypes of alpha2 adrenoceptors, their distribution within the central nervous system, and their specific action are clearly defined. This could result in a detailed therapeutic index of more selective and potent alpha2 agonists.