The Case for the Use of Acepromazine in Male Horses

Acepromazine is known to cause penile prolapse in male horses, although the mechanism is unknown.¹  The incidence of the problem is also not known and seems to be infrequent. Although temporary or permanent paralysis can be devastating, the benefits of the drug’s use must be weighed against possible adverse effects. Acepromazine is probably the longest-acting tranquilizer available (excluding the extremely long-acting tranquilizers such as reserpine and fluphenazine), making it very useful for shipping horses by plane or long distances. Additionally, there is less loss of balance with acepromazine (as is seen with the α-2 agonist–induced ataxia), making it useful for clipping, shoeing, and other routine management procedures. Acepromazine may be a better choice for sedation than the α-2 agonists for diagnostic and treatment procedures such as echocardiography,^2,3  bone scans,⁴  and treatment of esophageal obstructions.⁵  Although it may produce a decrease in gastrointestinal (GI) motility comparable to xylazine,⁶  it produces less GI stasis than detomidine or romifidine⁶  and may be useful for the treatment of laminitis⁷  and myopathy.

Acepromazine has also been associated with a protective effect against anesthetic-associated mortality⁸  and has been used as an adjunct to other drugs, for both standing anesthesia and general anesthesia. When used as a premedicant to general anesthesia, acepromazine may have a protective effect against hypoxemia associated with ventilation-perfusion mismatching.⁹ [...]