Acepromazine Maleate

Phenothiazine tranquilizer Antipsychotic / Neuroleptic

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog PO 0.5-2 mg/kg q8-12h as needed Duration: As needed for effect
Notes: Start at low end for tranquilization; higher doses for preanesthetic.
Dog IM 0.025-0.1 mg/kg (max 3 mg total) Single dose Duration: For preanesthetic or sedation
Notes: Do not exceed 3 mg total dose in dogs.
Dog IV 0.025-0.05 mg/kg (max 3 mg total) Single dose Duration: For rapid sedation
Notes: Administer slowly; monitor blood pressure.
Cat PO 0.5-2 mg/kg q8-12h as needed Duration: As needed for effect
Notes: Start at low end for tranquilization.
Cat IM 0.025-0.1 mg/kg (max 1 mg total) Single dose Duration: For preanesthetic or sedation
Notes: Do not exceed 1 mg total dose in cats.
Cat IV 0.025-0.05 mg/kg (max 1 mg total) Single dose Duration: For rapid sedation
Notes: Administer slowly; monitor blood pressure.
Horse IV 0.02-0.05 mg/kg Single dose Duration: For sedation
Notes: Administer slowly; may cause penile prolapse in stallions.
Horse IM 0.04-0.1 mg/kg Single dose Duration: For sedation
Notes: Onset slower than IV.
Cattle IM 0.05-0.1 mg/kg Single dose Duration: For sedation
Notes: Use with caution in debilitated animals.
Cattle IV 0.02-0.05 mg/kg Single dose Duration: For rapid sedation
Notes: Administer slowly.
Small Ruminants (Sheep/Goats) IM 0.05-0.1 mg/kg Single dose Duration: For sedation
Notes: Use with caution; may cause regurgitation.
Rabbit IM 0.5-1 mg/kg Single dose Duration: For sedation
Notes: Often combined with ketamine for anesthesia.
Bird (Poultry) IM 0.5-2 mg/kg Single dose Duration: For sedation
Notes: Dose varies by species; use lower end for small birds.

Clinical Indications & Species Uses

General Indications
  • Tranquilization and sedation
  • Preanesthetic medication
  • Antiemetic
  • Adjunct in behavioral therapy
Dog (Canine)
  • Tranquilization and sedation for handling, examination, and minor procedures
  • Preanesthetic medication
  • Antiemetic (especially for motion sickness)
  • Treatment of behavioral disorders (as adjunct)
  • Reduction of anxiety and fear
Cat (Feline)
  • Tranquilization and sedation for handling, examination, and minor procedures
  • Preanesthetic medication
  • Antiemetic (especially for motion sickness)
  • Treatment of behavioral disorders (as adjunct)
Horse (Equine)
  • Tranquilization and sedation for handling, examination, and minor procedures
  • Preanesthetic medication
  • Chemical restraint for transport or shoeing
Cattle (Bovine)
  • Tranquilization and sedation for handling, examination, and minor procedures
  • Preanesthetic medication
  • Chemical restraint for transport or minor surgery
Small Ruminants (Sheep / Goat)
  • Tranquilization and sedation for handling, examination, and minor procedures
  • Preanesthetic medication
Rabbit & Small Mammals
  • Tranquilization and sedation for handling, examination, and minor procedures
  • Preanesthetic medication (often combined with ketamine)
Avian & Poultry
  • Tranquilization and sedation for handling, examination, and minor procedures
  • Preanesthetic medication
Exotic & Other Species
  • Tranquilization and sedation in various exotic species (reptiles, small mammals) at species-specific doses

Pharmacology & Mechanism of Action

Drug Class: Phenothiazine tranquilizer | Pharmacological Group: Antipsychotic / Neuroleptic

Mechanism of Action: Acepromazine is a phenothiazine derivative that acts primarily as a dopamine receptor antagonist in the central nervous system. It blocks postsynaptic dopamine receptors in the brain, particularly in the mesolimbic and mesocortical pathways, leading to suppression of spontaneous activity, emotional reactivity, and motor activity. It also has alpha-adrenergic blocking activity, which contributes to its hypotensive effects, and weak anticholinergic and antihistaminic properties. The exact mechanism for its tranquilizing effect is not fully understood but is thought to involve depression of the brain stem and connections to the cerebral cortex.

Pharmacodynamics: Acepromazine produces dose-dependent sedation, tranquilization, and a decrease in motor activity. It has antiemetic effects due to dopamine blockade in the chemoreceptor trigger zone. It causes peripheral vasodilation and hypotension due to alpha-adrenergic blockade. It may lower the seizure threshold and can cause hypothermia due to effects on the thermoregulatory center. It has minimal analgesic properties. The onset of action is rapid after IV administration (within 5 minutes) and slower after IM (15-30 minutes) or oral (30-60 minutes). The duration of effect is typically 2-6 hours, but can be prolonged in some animals.

⚡ Pharmacokinetics Summary

Absorption: Well absorbed after oral and intramuscular administration. Onset of action is faster after IM (15-30 min) compared to oral (30-60 min).
Distribution: Widely distributed throughout the body, including the brain. Crosses the placenta. Protein binding is high (approximately 90%).
Metabolism: Extensively metabolized in the liver, primarily by oxidation and conjugation. Metabolites are excreted in urine and bile.
Excretion: Excreted primarily in urine as metabolites, with some fecal excretion. Elimination half-life varies by species, but is generally short (1-3 hours in dogs and cats).
Half-Life: Dogs: ~1-3 hours; Cats: ~1-2 hours; Horses: ~1-2 hours; Ruminants: ~1-2 hours (estimated).
Bioavailability: Oral bioavailability is variable, estimated at 20-50% due to first-pass metabolism. IM bioavailability is high.
Protein Binding: Approximately 90% bound to plasma proteins.

Available Formulations & Strengths

Oral Tablet 10 mg, 25 mg (PO)
Injectable Solution 10 mg/mL (IM, IV)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to phenothiazines
  • Severe hepatic disease
  • Severe cardiovascular disease or hypotension
  • Animals with a history of seizures (may lower seizure threshold)
  • Pregnant animals (especially near term) unless benefits outweigh risks
  • Concurrent use with other CNS depressants (use with caution)
  • Animals with phochromocytoma
  • Debilitated or geriatric animals (use with caution)
Warnings & Clinical Precautions:
  • May cause hypotension, especially after IV administration; monitor blood pressure.
  • Can lower seizure threshold; use with caution in epileptic animals.
  • May cause hypothermia; provide warmth if needed.
  • In horses, may cause penile prolapse and rarely paraphimosis; use with caution in breeding stallions.
  • In dogs, may cause paradoxical excitement in some individuals.
  • Use with caution in animals with respiratory compromise.
  • May cause prolonged sedation in animals with hepatic or renal impairment.
  • Not recommended for use in animals with glaucoma due to anticholinergic effects.
  • In food animals, observe withdrawal times.
  • Avoid extra-label use in animals intended for human consumption without proper withdrawal periods.

Adverse Effects & Reactions

Common:

  • Sedation
  • Hypotension
  • Hypothermia
  • Dry mouth
  • Mydriasis
  • Decreased respiratory rate
  • Paradoxical excitement (especially in dogs)

Serious / Severe:

  • Severe hypotension
  • Cardiac arrhythmias
  • Seizures (in predisposed animals)
  • Penile prolapse in horses
  • Neuroleptic malignant syndrome (rare)
  • Hepatic necrosis (rare)

Rare:

  • Blood dyscrasias (agranulocytosis, leukopenia)
  • Allergic reactions (urticaria, anaphylaxis)
  • Extrapyramidal signs (tremors, rigidity)
  • Cholestatic jaundice

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Other CNS depressants (barbiturates, opioids, anesthetics) Additive sedation and respiratory depression High
Anticholinergics (atropine) Increased anticholinergic effects (tachycardia, dry mouth) Moderate
Epinephrine Paradoxical hypotension due to alpha-adrenergic blockade High
Antihypertensives Additive hypotensive effects Moderate
Tricyclic antidepressants Increased risk of arrhythmias and anticholinergic effects Moderate
Organophosphates Increased toxicity due to cholinesterase inhibition Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • Severe CNS depression
  • Coma
  • Hypotension
  • Hypothermia
  • Respiratory depression
  • Seizures (in some cases)
  • Cardiac arrhythmias

Emergency Treatment Protocol: Treatment is primarily supportive. Maintain airway, breathing, and circulation. Administer IV fluids to support blood pressure. Use vasopressors (e.g., norepinephrine) if hypotension is severe; avoid epinephrine. Control seizures with diazepam or barbiturates. Provide warmth to treat hypothermia. Monitor cardiac function. There is no specific antidote; symptomatic and supportive care is essential.

Food Animal Withdrawal Times

🥩 Meat: 7 days🥛 Milk: 48 days

Withdrawal times vary by country and formulation. In the US, acepromazine is not approved for food animals, but extra-label use requires extended withdrawal periods. Consult regulatory guidelines. For cattle, a meat withdrawal of 7 days and milk withdrawal of 48 hours is commonly recommended, but verify with local regulations.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25°C (68-77°F), excursions permitted between 15-30°C (59-86°F).

Light Sensitivity: Light-sensitive — protect from direct exposure.

Handling & Special Conditions: Protect from light. Keep container tightly closed. Do not freeze.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in dogs, cats, and horses. Not approved for food animals in the US.

Extra-Label (Off-Label) Use: In the US, acepromazine is not approved for use in food animals. Extra-label use in food animals is permitted under AMDUCA with a valid veterinary-client-patient relationship, but requires extended withdrawal times to ensure food safety. In non-food animals, extra-label use is common and accepted.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Acepromazine is a widely used phenothiazine tranquilizer in veterinary medicine. It is effective for sedation, preanesthetic medication, and as an antiemetic. It is important to use the lowest effective dose to minimize adverse effects, particularly hypotension and hypothermia. In dogs and cats, the total dose should not exceed 3 mg and 1 mg, respectively, to avoid severe adverse effects. In horses, acepromazine should be used with caution due to the risk of penile prolapse. It is not a controlled substance, but it is a prescription drug. Always monitor animals closely after administration, especially when used in combination with other CNS depressants. For food animals, adhere to withdrawal times to ensure food safety.

References & Literature

  • 📚 Plumb's Veterinary Drug Handbook
  • 📚 Papich Veterinary Pharmacology and Therapeutics
  • 📚 Compendium of Veterinary Products (CVP)