Acepromazine

Acepromazine or Acetylpromazine (More commonly known as ACP, Ace, or by the trade name Atravet or "Acezine 2" etc, number depending on mg/ml dose) is one of the phenothiazine derivative psychotropic drugs, used little in humans, however frequently in animals as a sedative and antiemetic. Its principal value is in quietening and calming frightened and aggressive animals. The standard pharmaceutical preparation, acepromazine maleate, is used extensively in equine, feline, and canine; especially as a pre-anesthetic agent often in conjunction with Atropine, and often an opiate such as morphine or buprenorphine. Its depressive cardiopulmonary effects can be profound and as such is not recommended for use in geriatric or debilitated animals, (often substituted with midazolam in these cases, or left out of the premed cocktail all together).

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Administration

Canine: When used as a premedication it is commonly administered via the subcutaneous route. ACP should not be used in sighthounds.

In the Boxer, it tends to cause a problem called first degree heart block, a potentially serious arrhythmia of the heart. It also causes a profound hypotension (severe lowering of the blood pressure) in many Boxers that receive the drug. On the Veterinary Information Network, a computer network for practicing veterinarians, an announcement was placed in the cardiology section entitled "Acepromazine and Boxers." This described several adverse reactions to the drug in a very short time span at a veterinary teaching hospital. All the adverse reactions were in Boxers. The reactions included collapse, respiratory arrest, and profound bradycardia (slow heart rate, less than 60 beats per minute). The announcement suggested that Acepromazine should not be used in dogs of the Boxer breed because of a breed related sensitivity to the drug.

Equine: Acepromazine is normally given by the intramuscular route, taking 30-45 minutes to take effect. It may also be given intravenously (taking only 15 minutes to take effect) or orally. Sedation usually lasts for 1-4 hours, although some horses may feel the effects for up to 24 hours. The standard dose is highly variable, depending upon effect, and is not authorised for use in horses intended for human consumption. In equine surgery, premedication with acepromazine is known to reduce the perianaesthetic mortality rate (Johnston et al. (2002), although the reasons for this are unclear.

An additional usage is as a vasodilator in the treatment of laminitis, where a "mild sedation" dose orally is commonly used, although the dose used is highly dependant on the treating veterinarian. It is also sometimes used to treat a horse experiencing Equine Exertional Rhabdomyolysis.

An oral formulation is also available, as a gel (Sedalin gel). The dosage by this route is also highly variable, but it is generally accepted that the recommended dose will give moderate sedation in most animals.

Precautions when using in horses

Acepromazine is a prohibited class A drug under FEI rules, and its use is prohibited or restricted by many other equestrian organizations. It can be detected in the blood for 72-120 hours, although repeated doses may make it remain present for several months.

Side effects are not common, but the use of acepromazine in stallions is usually considered contraindicated due to the risk of paraphimosis.

Acepromazine should not be used in horses dewormed with piperazine. It lowers blood pressure, and should therefore be used with caution in horses that are experiencing anemia, dehydration, shock, or are colicing.

References

• GM Johnston, JK Eastment, JLN Wood, PM Taylor (2002), "The confidential enquiry into perioperative equine fatalities (CEPEF): mortality results of Phases 1 and 2," Veterinary Anaesthesia and Analgesia 29 (4), 159–170.
• NOAH, Compendium of Data Sheets for Animal Medicines 2005.
• Forney, Barbara C, MS, VMD. Equine Medications, Revised Edition. Blood Horse Publications. Lexington, KY. Copyright 2007.