Detomidine

Detomidine is an imidazole derivative and alpha2-adrenergic agonist, used as a large animal sedative,primarily used in horses. Usually available as detomidine hydrochloride. This is a prescription medication available to veterinarians sold inder the trade name Domosedan.

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Properties

Detomidine is a sedative with analgesic properties. Alpha2-adrenergic agonists produce dose-dependent sedative and analgesic effects, mediatated by activation of alpha-2 catecholamine receptors, thus inducing a negative feedback response, reducing production of excitatory neurotransmitters. Due to inhibition of the sympathetic nervous system, detomidine also has cardiac and respiratory effects and an antidiuretic action.

Effects

A profound lethargy and characteristic lowering of the head with reduced sensitivity to environmental stimuli (sounds, etc.) are seen with detomidine. A short period of in-coordination is characteristically followed by immobility and a firm stance with front legs spread. Following administration there is an initial increase in blood pressure, followed by bradycardia and second degree atrioventricular block (this is not pathologic in horses). The horse commonly sweats to excess, especially on the flanks and neck. Other side effects reported include pilo erection (hair standing erect), ataxia, salivation, slight muscle tremors, and (rarely) penile prolapse.

Uses

Sedation and anaesthetic premedication in horses and other large animals, commonly combined with butorphanol for increased analgesia and depth of sedation. In conjunction with ketamine it may also be used for intravenous anaesthesia of short duration. Detomidine is only licenced for use in horses at the present time. The drug is normally administered by the intravenous route, and is fastest and most efficient when given i/v (usually 2-5 minutes to take effect, although this is highly dependent upon the individual and the environment. Some horses are highly resistant to sedation!). However, in recalcitrant animals, detomidine may be administered by the intramuscular or sublingual routes. The dose range advised by the manufacturers is 20-40 mcg/kg i/v for moderate sedation. This dose may need to be higher if given i/m.

Cautions

As detomidine is an arrhythmogenic agent, extreme care should be exercised in horses with cardiac disease, and in the concurrent administration of other arrhythmogenics. The concurrent use of potentiated sulphonamide antibiotics is considered particularly dangerous.

References

• The Ontario Association of Equine Practitioners, Medication Protocols for Horses 2005
• NOAH Compendium of Data Sheets for Animal Medicines 2005