Acepromazine is one of the most commonly used sedatives/tranquilizers in small animal veterinary practices.

In horses, acepromazine is labeled for use as an aid in controlling fractious animals and in conjunction with local anesthesia for various procedures and treatments. It is also used in horses at low doses as a preanesthetic agent for mild sedation. Acepromazine has been used in horses with laminitis to improve blood flow to the distal limb.^2–4

Acepromazine does not provide analgesia, thus, the inclusion of an analgesic agent is required when pain relief is needed.

The Fractious Horse

Stallions and mares can be behaviorally challenging in equine facilities, with both having the potential to exhibit different behavioral problems. Amongst horse owners, managers and enthusiasts, mares have a certain reputation as regards their behavior, and this is typically attributed to their estrus cycle. Estrus is the recurring cycle of sexual receptivity in the mare and, as in other mammals (including humans), involves a complex hormonal dynamic that is known to affect behavior. 

There are medications available that can be used to suppress estrus (heat),⁵ but depending on the circumstances and requirements (such as with mares in breeding programs), the owner or manager may wish to address the behavior without suppressing estrus.

Stallions are intact male horses, as opposed to geldings, which are castrated male horses. Their natural high energy is exacerbated when mares in season are present, and is one of the reasons for the practice of castration in males that are not intended for breeding. The behavior of stallions in the presence of mares often leads to skittishness, aggression and other behavioral problems. 

Of course, there are also other factors that may be related to the individual horse’s innate demeanor that can negatively affect its behavior. Once lameness, illness or other issues that might be resolved through training or handling methods are ruled out, the horse owner, manager or veterinarian is faced with discerning the most appropriate method for behavior modification.

Acepromazine Maleate for Horses

Acepromazine maleate has the best effect when given orally 45 to 60 minutes before a procedure or travel. Sedative or tranquilizing effects and side effects may last up to 24 hours. The veterinarian may recommend a trial dose prior to travel to determine the horse reacts to the medicine. In some cases, animals sedated with acepromazine maleate may startle easily in response to sounds or other sudden stimuli. It is recommended that caution is used when approaching horses should this occur, since this effect may make them more aggressive.

Precautions and Adverse Effects

In male horses, paralysis of the retractor penis muscle has been noted with the use of acepromazine/acepromazine maleate. The risk for this syndrome should be considered prior to the administration of these medications. Dosage should be limited to the minimum amount necessary for the desired effect. At the time of administration, it is normal to observe the reversible protrusion of the penis. The irreversible paralysis of the retractor penis muscle may occur when a tranquilizer is used in conjunction with testosterone (or in stallions).⁶

Where to buy Acepromazine Maleate

Acepromazine maleate is available in the U.S. through pharmaceutical manufacturers and through veterinary custom compounding companies. 

Acepromazine maleate carries numerous potential drug interactions. Please consult your veterinarian prior to beginning any treatment regimen.

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

²Coleman M. Laminitis. In: Large Animal Internal Medicine. 6th ed. Elsevier ; 2020:1235-1238.

³Leise B.S., et. al. Effects of intramuscular administration of acepromazine on palmar digital blood flow, palmar digital arterial pressure, transverse facial arterial pressure, and packed cell volume in clinically healthy, conscious horses. Vet Surg. 2007; 36(8):717-723. doi:10.1111/j.1532-950X.2007.00325.

⁴Ingle-Fehr J.E., et. al. The effect of oral isoxsuprine and pentoxifylline on digital and laminar blood flow in healthy horses. Vet Surg. 1999;28(3):154-160. doi:10.1053/jvet.1999.0154.

⁵horsesport.com.

⁶equimed.com.