Alpha2-adrenoceptor agonists

Alpha2-adrenoceptor agonists produce profound sedation and moderate to profound analgesia.

Alpha2-adrenoceptors’s stimulation in the brain results in a decrease in the release of norepinephrine (noradrenaline) in the brain resulting in sedation and analgesia.

The side effects associated with alpa2-adrenoceptor agonists are associated with their effects at other alpha2-adrenoceptors (e.g. in the pancreas where the result is a reduction in insulin and thus transient hyperglycaemia, which can be associated with polyuria/diuresis) and at alpha1-adrenoceptors.

Medetomidine has a ten-times greater affinity for alpha2-adrenoceptors than xylazine and lower affinity for alpha-1 receptors (which mediate many of the adverse effects). As a result, medetomidine has greater potency and fewer adverse effects than xylazine.

These agents are used primarily to provide sedation. They also provide some pain relief. They are usually used in combination with butorphanol as part of neuroleptanalgesia.

• Medetomidine (potent analgesic; more potent than xylazine; numerous side effects including cardiovascular depression).