Pharmacodynamics of alpha2-adrenoceptor agonists

Two α2-agonists are currently available for peri-operative use—clonidine and dexmedetomidine. These α2-agonists have sympatholytic, analgesic, sedative and anxiolytic properties, resulting in diverse pharmacodynamic effects that make them useful as peri-operative anaesthetic adjuncts. Their main cardiovascular effects are a decrease in blood pressure and heart rate. Peri-operatively they reduce the amount of hypertension and tachycardia, thus improving haemodynamic stability. Their sedative effects are dose dependent, and with appropriate doses, patients remain rousable. The combination of the haemodynamic and sedative effects makes α2-agonists especially suitable for post-operative or ICU patients with increased sympathetic nervous system tone. Some of the other clinical effects of these drugs are anxiolysis, a reduction of anaesthetic and opioid requirements, analgesia and the prevention of shivering. They have a minimal effect on respiration. The side-effects include bradycardia and hypotension.