Detomidine for Horses: A Superior Solution for Sedation

Standing sedation is a critical component in many key procedures done on-site and in the equine veterinary clinic. When choosing between the available sedation drugs, veterinarians must consider safety, cost effectiveness for the client and the practice, and – above all – the ultimate efficacy of the product in achieving an appropriate level of sedation for the needed procedure.¹

Detomidine hydrochloride is a drug that came onto the scene in the mid-1980s; generics for detomidine were approved by the U.S. Food and Drug Administration (FDA) in April 2020.² Detomidine was found by veterinarians to be a superior drug for standing sedation in horses, as well as not exhibiting the same adverse effects as xylazine.³

Detomidine HCl is a non-narcotic sedative and analgesic, and a potent α2-adrenoreceptor agonist which produces a dose dependent sedation and superficial and visceral analgesia. Marked lethargy and a characteristic lowering of the head with reduced sensitivity to environmental stimuli (sounds, etc.) are seen with detomidine.⁴ A short period of poor coordination is followed by immobility and a firm stance with front legs well spread.

Detomidine’s analgesic effect is most readily seen as an increase in the pain threshold at the body surface. It provides the veterinarian with the benefits of analgesia at a much higher level than that offered by drugs such as xylazine hydrochloride or romifidinehydrochloride.² The value of an analgesic added to sedation can be clearly seen in equine dental practices, particularly during extensive dental procedures and standing surgeries.

Detomidine HCl: Indications and Action

Detomidine is indicated for use as a sedative and analgesic to facilitate minor surgical and diagnostic procedures in mature horses and yearlings. It has been used to calm fractious horses, to provide relief from abdominal pain, to facilitate bronchoscopy, bronchoalveolar lavage, nasogastric intubation, nonreproductive rectal palpations, suturing of skin lacerations, and castrations.² An approved, local infiltration anesthetic is also indicated for castration.

With detomidine administration, heart rate is markedly decreased, blood pressure is initially elevated, and then a steady decline to normal is seen.² A transient change in the conductivity of the cardiac muscle may occur, as evidenced by partial atrioventricular (AV) and sinoauricular (SA) blocks. This change in the conductivity of the cardiac muscle may be prevented by IV administration of atropine at 0.02 mg/kg of body weight.¹

No effect on blood clotting time or other hematological parameters was encountered at dosages of 20 or 40 mcg/kg of body weight.² Respiratory responses include an initial slowing of respiration within a few seconds to 1-2 minutes after administration, increasing to normal within 5 minutes. An initial decrease in tidal volume is followed by an increase.¹

Drug Combinations

Combining opioids (morphine, butorphanol) with α2- agonists will produce a state referred to as neuroleptanalgesia, in which the level of sedation and analgesia is more profound and greatly im-proves the chemical restraint. The opioids can be used as a single bolus for short procedures or, for longer procedures, as multiple intermittent boluses or as a loading dose followed by a CRI. Combinations of detomidine and morphine are very useful for procedures expected to be associated with strong noxious stimulation such as (but not limited to)ovariectomy and tooth extraction.⁶

Horses sedated with detomidine and morphine are typically less responsive to noxious as well as non-noxious stimulation. However, local blocks are still required to facilitate most surgical procedures.² When given as a CRI, this combination produces stable sedation that can be relatively easily adjusted as needed.

The available literature strongly asserts that horses that are deeply sedated with α2-agonist are not unconscious. A sedated horse must be handled with caution, since it may be aroused by stimulation and can respond with dangerous kicks. In situation in which painful procedures are planned, or local analgesia needs to be placed before surgery on the standing horse, accentuation of both sedation and analgesia can be achieved by adding an opioid to the α2-agonist.⁵

It has been observed that significantly more detomidine and morphine may be required to produce satisfactory chemical restraint in horses undergoing extensive dental procedures (i.e., root canals, multiple dental extractions). Some of these horses may have significant bradycardia and require treatment with an anticholinergic such as butylscopolamine. It can be given as small doses (0.05– 0.1mg/kg IV) as needed to maintain heart rate within an acceptable range for the patient.⁴

Horses sedated with detomidine and morphine, especially those undergoing prolonged procedures, will also receive a crystalloid solution such as lactated Ringer’s solution (2–5 mL/kg per hour) to maintain fluid balance and replace losses caused bypolyuria. These horses also typically receive mineral oil through a nasogastric tube at the end of the procedure and are kept on colic watch for the following 24 hours. Morphine is avoided, used at the lowest possible doses, or replaced with butorphanol in horses with a recent history of colic. Antagonism of detomidine or morphine is typically not needed, but could be performed with the appropriate antagonists.⁵

A Proven Level of Analgesia

While sedation is often the veterinarian’s chief consideration in standing procedures such as dental care, suturing wounds and castrations, choosing a drug that provides a proven level of analgesia offers a more humane option for clients and their horses. Although sedation works to depress the horse’s brain, a drug with an analgesic effect will also help to deaden pain for the animal, allowing for less reliance on the twitch and fewer reactions during a painful procedure.⁴

Many veterinarians report that by using detomidine as a simple, one-sedative variable the veterinarian has more control over the level of sedation and analgesia. Additionally, more precise dosing can be achieved, decreasing the need for second doses during procedures.¹ These considerations mean a less traumatic experience for the horse, and they help to decrease the chance of injury to the owner or veterinarian during procedures.