Xylazine, 5, 6-dihydro-2-(2, 6-xylidino)-4H-1, 3-thiazine, is a thiazine derivative with sedative, hypnotic, local anaesthetic and hypotensive properties. It also has muscle relaxant and analgesic effects; the degree of relaxation/analgesia depends upon the animal species.

Xylazine is an agonist of the alpha-2 adrenergic receptors. It acts on pre-synaptic and post-synaptic receptors of the central and peripheral nervous system. Both the sedation and the analgesia are due to stimulation of central alpha-2 adrenergic receptors.

Xylazine is absorbed extremely rapidly and distributed widely throughout tissues. After intramuscular injection maximum plasma concentrations are achieved within 12-14 minutes in all species.

Bioavailability varies after intramuscular injection; in the dog it is between 52 and 90%, in the sheep. 17-73% and in the horse 40-48%. Metabolism is extremely rapid. The molecule is broken down into several metabolites. Elimination after intramuscular and intravenous application takes place with a half-life of between 23 and 60 minutes depending on species. The half-life for total elimination, which is dependent on the route of administration and dosage, is 2-3 hours.

Analeptics will shorten the period or reduce the depth of sedation. Alpha-2 blockers such as atipamazole are effective in reversing the sedation and other physiological effects of the drug.