Acepromazine, acetopromazine, or acetylpromazine (commonly known as ACP, Ace, or by the trade names Atravet or Acezine 2, number depending on mg/ml dose) is a phenothiazine derivative antipsychotic drug. It was used in humans during the 1950s as an antipsychotic, but is now almost exclusively used on animals as a sedative and antiemetic. Its closely related analogue, chlorpromazine, is still used as an antipsychotic in humans. Acepromazine is used primarily as a chemical restraint in hyperactive or fractious animals. It can also be used to lower the seizure threshold. The standard pharmaceutical preparation, acepromazine maleate, is used in veterinary medicine in dogs and cats. It is used widely in horses as a pre-anesthetic sedative and has been shown to reduce anesthesia related death. However, it should be used with caution (but is not absolutely contraindicated) in stallions due to the risk of paraphimosis and persistent priapism. Its potential for cardiac effects can be profound, namely hypotension due to peripheral vasodilation, so it should be avoided or used with caution in geriatric or debilitated animals. Pharmacology The clinical pharmacology of acepromazine is similar to that of other phenothiazine derived anti-psychotic agents. The primary behavioral effects are attributed to its potent antagonism of post-synaptic D2 receptors and, to a lesser degree, the other D2-like receptors. Additional effects are related to its appreciable antagonistic effects on various other receptors, including the α1-adrenergic receptors, H1 receptors, and muscarinic acetylcholine receptors. It is metabolized by the liver, oxidized to produce its primary metabolite, hydroxyethylpromazine sulfoxide, which is then excreted in the urine. Its action at the chemoreceptor trigger zone (in the area postrema) and the solitary nucleus (in the medulla oblongata) allow it to have an antiemetic effect. Veterinary use Canine and feline The most common uses of acepromazine in animals are as an oral sedative before stressful events (such as thunderstorms), an injectable tranquilizer for particularly aggressive or fractious animals, and in combination with analgesics and other sedatives. It is also labeled for use in preventing motion sickness. Its effects as a CNS depressant means that less opiates are required to reach the same amount of sedation, and it prevents the arrhythmia and vomiting that many opiates induce. Adverse effects in cats While acepromazine is also used in cats, its absorption is erratic and can differ wildly from one cat to the next. It also generally induces less sedation than in dogs. It also