ACEPROMAZINE

Acepromazine is used in dogs, cats, horses, pigs and cows as sedative, tranquilliser, preanaesthetic, anaesthetic adjunct, muscle relaxant, behaviour modifying agent etc.

Acepromazine is also known as acetopromazine and acetylpromazine. It is a phenothiazine derivative and available as acepromazine maleate in injections and tablets.

MECHANISM OF ACTION

Acepromazine inhibits central dopaminergic receptors to produce sedation and tranquillisation. Acepromazine also has antimuscarinic action and blocks norepinephrine at adrenergic receptors (alpha-receptors). Because of the blockade of alpha-receptors on vascular smooth muscle, it also produces vasodilation. When administered as an anaesthetic adjunct, it may produce a decrease in vascular resistance and lower blood pressure but usually does not decrease cardiac output. In horses, IV administration significantly increases the blood flow through digital arteries and laminae. The half-life in horses is approximately 2.5 hours.

CLINICAL USES

Acepromazine is used as a sedative, a tranquilliser, a preanaesthetic, and an anaesthetic adjunct. When used as an anaesthetic and preanaesthetic, it induces muscle relaxation and lowers doses of anaesthetic agents used concurrently. In pre-anaesthetic protocols, it also may have some anti-arrhythmic effects. In small animals, duration of sedation can occur within 10 minutes and have a 4- to 6-hour duration. In small animals, acepromazine can produce antiemetic effects via dopaminergic blockade. Acepromazine produces arterial smooth muscle relaxation by inhibiting alpha1 receptor mediated constriction. This effect is used to increase blood flow to tissues, particularly in the metatarsal artery of horses, and produces increased blood flow to the palmar digital artery. This is used for the treatment of horses with laminitis.

Acepromazine has been used as a behaviour modifying agent in animals (to treat anxiety). However, there are other agents that are preferred for long-term management of behaviour disorders in animals that have fewer adverse effects. It should not be used as a first choice to decrease stress in hospitalised animals because there are other preferred agents available. Acepromazine does not provide analgesic activity.

SIDE EFFECTS

Sedation and ataxia are common side effects. Extrapyramidal effects (involuntary muscle movements), twitching, dystonia, or Parkinson-like effects are rare but are possible with the administration of phenothiazines to animals. Acepromazine may produce paradoxical excitation, disinhibition, and aggression in some dogs.

Phenothiazines may produce excessive vagal tone in some animals. This may be especially prominent in brachycephalic breeds. Administration of atropine may be used to treat the signs of high vagal tone. Because of alpha-adrenergic antagonism, hypotension is possible in animals. Decreased vascular tone because of alpha1 adrenergic blockade is a prominent effect of acepromazine. This may produce hypotension in susceptible animals.

Dogs with a mutation in the ABCB1 gene may be deficient for the ABCB1 transporter (p-glycoprotein). These dogs may have increased sensitivity to the effects of acepromazine, resulting in greater sedation scores. Lower doses should be used in these dogs.

In horses, persistent penile prolapse has been reported from use. This effect on horses is unpredictable. Some resources indicate that it is dose dependent, with increased likelihood as the dose is increased from 0.01 to 0.1 mg/kg IV. The duration of penile prolapse in horses may be as long as 4 hours with high doses. In rare cases, penile prolapse can lead to permanent paraphimosis. The mechanism is unknown but may be caused by the alpha-adrenergic blockade induced by acepromazine.

CONTRAINDICATIONS

It has been stated in some veterinary textbooks that acepromazine may increase the risk of seizures in animals, and it should be administered cautiously in animals that are prone to seizures. However, a risk of seizures in animals from administration of acepromazine has not been confirmed during clinical use. Seizures were not reported in retrospective studies in which animals prone to seizures were anaesthetized and administered acepromazine as an anesthetic adjunct.

Do not use in animals that have problems with dystonia or that have had previous extrapyramidal effects from use of phenothiazines.

Dogs with a mutation in the ABCB1 gene (previously listed as MDR1), which is the gene that codes for the p-glycoprotein membrane transporter, are likely to have prolonged and increased sedation after administration of acepromazine. In these dogs, the dose should be decreased or another sedative selected for use.

Phenothiazines can cause hypotension (via alpha-receptor blockade); therefore, use cautiously with other hypotensive drugs or in conditions that may exacerbate hypotension. When administered as a pre-anaesthetic to dogs (0.05 mg/kg), it induces moderate hypotension but does not affect cardiac output significantly.

In pregnancy, it produces only a minor reduction in blood flow and oxygen delivery to the fetus when used in late pregnancy in cows.

DRUG INTERACTIONS

Specific drug interactions have not been reported from the use of acepromazine in animals. However, it exacerbates the effects of other sedative drugs and may potentiate other drugs that cause vasodilation. Acepromazine has been used to sedate dogs for glucose tolerance testing (0.1 mg/kg) without adversely affecting the results.

PRECAUTIONS

Acepromazine can be administered PO, IV, or IM. The doses used in anesthetic protocols are usually lower than the label dose. When used with general anesthetics, lower doses of general anesthetics can be used, especially when administering barbiturates and inhalant anesthetics. Clinical signs from acepromazine administration are most prominent during the first 3–4 hours after administration but may persist for 7 hours.

MONITORING

Monitor blood pressure in animals susceptible to hypotension. Acepromazine does not affect adrenal function testing in dogs.

FORMULATIONS

Injectables:

Acepromazine is available in 5mg/mL injections.

Tablets:

Acepromazine is available in 5mg, 10mg, and 25mg tablets.

Syrup/Suspensions:

No acepromazine syrup/suspensions available.

Other formulations:

No acepromazine other formulations (inhaler, respule) available.

STORAGE

Acepromazine should be stored in a tightly sealed container, protected from light, and at room temperature. Stability of compounded formulations has not been investigated.

DOSE RATE

Dose rates for various animals are listed below. Adjust the dose rates according to the pathophysiology and conditionNo of each case.

DOGS

0.025–0.1 mg/kg IM, IV, or SQ in a single dose (most common is 0.025 mg/kg). Do not exceed 3 mg total in dogs.
Sedation: 0.5–2.2 mg/kg q6–8h PO.
Anesthetic protocols: 0.01–0.05 mg/kg IV, administered with other agents

CATS

0.025–0.1 mg/kg IM, IV, or SQ in a single dose.
Sedation: 1.1–2.2 mg/kg q6–8h PO.
Anesthetic protocols: 0.01–0.05 mg/kg IV, administered with other agents.

HORSES

0.04–0.1 mg/kg IM. It can be administered q6–12h, but such frequent dosing is not recommended, and an interval of 36–48 hours between doses is preferred. For perioperative use, 0.01–0.05 mg/kg, IM, SQ, or IV.
Treatment of laminitis: 0.04 mg/kg, IV.

CATTLE

0.13–0.26 mg/kg PO, 0.03–0.1 mg/kg IM, or 0.01–0.02 mg/kg IV.

PIGS

Adult: 0.03–0.2 mg/kg IV, IM, SQ (single dose).

ADMINISTRATION

Acepromazine typically administered via intravenous (IV), intramuscular (IM), subcutaneous (SC) and per oral (PO) routes. It is essential to check the label for specific preparation instructions since certain formulations may be designated for specific routes of administration.

ORAL BIOAVAILABILITY

A bioavailability of 55% can be expected for acepromazine when administered orally.

PROTEIN BINDING

Protein binding for acepromazine ranges from 95% to 99%.

ELIMINATION HALF LIFE

The elimination half-life for acepromazine is approximately 50 to 150 minutes.

METABOLISM

Metabolism of acepromazine takes place in the Liver.

EXCRETION

Excretion of acepromazine takes place in the Kidneys.

ANTIDOTE

No specific antidote. Doxapram, Phenylephrine, Norepinephrine and Diazepam used accordingly to reverse the effect.

NOTES

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