Many surgical and diagnostic procedures can be accomplished in standing horses if appropriate combinations of physical and chemical restraint are employed. The ability to perform procedures in the standing position is more important in the horse than in other species because of the greater risk of complications associated with anesthesia in equine species.¹ This is of increased concern in the case of procedures in mature horses.

There are numerous drugs approved for use in horses for standing chemical restraint. Among these are acepromazine, butorphanol, chloropent, detomidine, pentazocine, promazine, romifidine, triflupromazine and xylazine. Narcotic sedatives such as morphine and fentanyl, have been used occasionally for standing chemical restraint, but these are not labeled for use in the horse.

There is no single drug produces “ideal” standing chemical restraint in all horses.² Thus, the majority of equine veterinarians use these drugs in combination for sedation and analgesia with the goal of optimizing the onset, quality, and duration of the alteration in mental state while minimizing potentially deleterious side effects.

α-2 Agonists in Combination

The α-2 agonists, such as xylazine and detomidine, produce sedation with muscle relaxation, ataxia, and analgesia when given orally, intravenously, or intramuscularly. α-2 agonists produce a number of cardiorespiratory and other side effects, the significance of which are dose dependent in the clinical dose range. Heart rate decreases, and sinus arrhythmia, first degree atrioventricular blockade, and second degree atrioventricular blockade are common. Arterial blood pressure is initially in-creased because of drug-induced increases in peripheral vascular resistance.³

According to the available literature, when employing α-2 agonists, respiratory rate is usually decreased, but tidal volume increases to compensate for the drop.² Relaxation of the muscles of the upper airway occurs and can predispose the horse to stridor.⁶ The administration of an α-2 agonist decreases salivation, gastric secretions, and gastrointestinal motility, and it also increases urine volume.^7,8 Swallowing is depressed, and thus, passage of nasogastric tubes maybe more difficult.²

Xylazine and Detomidine

In addition to the above, xylazine’s analgesic properties have made it a mainstay in veterinary medicine for decades. Detomidine, like xylazine, is an α-2-adrenergic agonist that produces a dose-dependent sedative and analgesic effect, but it also has cardiac and respiratory effects. Detomidine is a more specific α-2 receptor agonist than xylazine, and it has an α-2/α-1 specificity of 260:1 compared with 160:1 for xylazine.⁵ Detomidine is 100 times more potent than xylazine, and has a duration of action approximately twice as long.² Detomidine is frequently used to manage pain in both mature horses and yearlings when undergoing minor surgical procedures, such as the repairing of skin lacerations, as well as diagnostics. It is also used in many diagnostic procedures in mature horses and yearlings.  

FOR RX ONLY: A valid prescription from a licensed veterinarian is required for dispensing this medication.

¹Johnston GM, Eastment JK, Wood JLN, et al. The confidential enquiry into perioperative equine fatalities (CEPEF):mortality results of Phases 1 and 2. Vet Anaesth Analg 2002;29:159 –170.

²Hubbell, J., DVM. Practical Standing Chemical Restraint of the Horse. Int J Appl Res VetMed2005;3:249 –258.

³Wagner AE, Muir WW, Hinchcliff KW. Cardiovascular effects of xylazine and detomidine in horses. Am J Vet Res1991;52:651–657.

⁵Freeman SL, England CG. Investigation of romifidine and detomidine for the clinical sedation of horses. Vet Rec2000;147:507–511.

⁶Lavoie JP, Pascoe JR, Kurpershoek CJ. Effect of head and neck position on respiratory mechanics  in horses sedated with xylazine. Am J Vet Res1992;53:1652–1657.

⁷Trim CM, Hanson RR. Effects of xylazine on renal function and plasma glucose in ponies. Vet Rec1986;118:65– 67.11. 

⁸Rutkowski  JA,  Ross MW, Cullen K. Effects of  xylazine and/or butorphanol or neostigmine on myoelectrical activity of the cecum and right ventral colon in female ponies. Am JVet Res1989;50:1096 –1101.