Acepromazine
Acepromazine maleate
Also known as: PromAce · Aceproject · Aceprotabs · Plegicil · Notensil · Atravet · Acecare · ACP · Acetylpromazine maleate
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Reviewed non-calculator evidenceReviewed non-calculator evidence (1)
Evidence only — not for automatic calculation
Tranquilization
a) Tranquilization: 0.25 – 0.75 mg/kg IM or SC 46 ; the lower to mid-range of the dosage is generally adequate.
Governing clinical context (4)
- 1. Acepromazine does not provide analgesia; addition of an analgesic agent is required when pain relief is needed.
- All dosages are extra-label.
- Store tablets and injection protected from light at 20°C to 25°C (68°F-77°F), with excursions permitted between 15°C and 30°C (59°F-86°F). Tablets should be stored in tight containers. There is no limit to the number of vial punctures throughout the full expiry period. 1
- 2. Administer IV doses slowly; allow at least 15 minutes for onset of action. 1
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Acepromazine is a classic, widely utilized phenothiazine neuroleptic agent in veterinary medicine, primarily used for its reliable tranquilizing and sedative properties.
Key Clinical Points:
- No Analgesia: Acepromazine provides zero pain relief. It must be combined with appropriate analgesics (e.g., opioids) for painful procedures (neuroleptanalgesia).
- Cardiovascular Effects: It is a potent vasodilator due to alpha-1 adrenergic blockade, frequently causing hypotension. It should be avoided in hypovolemic, shocked, or hemodynamically unstable patients.
- Breed Sensitivities: Giant breeds and sight hounds (e.g., Greyhounds) are highly sensitive. Dogs with the MDR1 (ABCB1) gene mutation (e.g., Collies, Australian Shepherds) require significant dose reductions (25-50%).
- Equine Considerations: May cause prolonged penile protrusion or priapism in stallions, which can lead to permanent paralysis of the retractor penis muscle.
While historically used for travel anxiety or noise phobias, modern veterinary behaviorists often discourage its use as a monotherapy for these conditions, as it may sedate the animal without reducing the underlying fear or panic, potentially increasing noise sensitivity.
Mechanism of action
Acepromazine exerts its effects through multiple receptor antagonisms:
- Dopamine (D2) Receptor Antagonism: Blocks postsynaptic D2 receptors in the CNS (specifically the basal ganglia and limbic system) → depresses the reticular activating system → produces sedation and tranquilization.
- Alpha-1 Adrenergic Antagonism: Blocks peripheral alpha-1 receptors → causes peripheral vasodilation → leads to hypotension and secondary hypothermia.
- Additional Blockade: Possesses varying degrees of anticholinergic (muscarinic), antihistaminic (H1), and antispasmodic effects.
- Antiemetic Effect: Blocks dopamine receptors in the Chemoreceptor Trigger Zone (CRTZ) of the medulla.
Clinical Pearl: Because of its alpha-blocking properties, administering epinephrine to an acepromazine-induced hypotensive patient can cause "epinephrine reversal" (unopposed beta-2 vasodilation), worsening the hypotension. Alpha-agonists like phenylephrine are preferred for treating severe acepromazine-induced hypotension.
Safety & warnings
Contraindications
- Significant cardiac disease
- Hypovolemia, hypotension, or shock
- Tetanus or strychnine intoxication
- Intra-arterial injection in horses (can cause severe CNS excitement, seizures, death)
- Use with extreme caution in very young, geriatric, or debilitated animals
- Avoid in racing animals within 4 days of a race
Adverse effects
- Hypotension and cardiovascular collapse
- Bradycardia (vagally mediated) or reflex tachycardia
- Hypothermia or hyperthermia
- Penile protrusion/prolapse in large animals (especially stallions)
- Prolapse of the membrana nictitans (third eyelid)
- Decreased tear production (especially in cats)
- Paradoxical excitement, restlessness, or aggression
- Transient pain at IM injection sites
- Decreased hematocrit (due to splenic sequestration of RBCs)
Precautions
Dosage Adjustments: The manufacturer's labeled dose is often considered up to 10 times higher than clinically necessary. Use lower end of dose ranges.
Breed Sensitivities:
- MDR1 Mutation: Dogs with the MDR1 (ABCB1) mutation (Collies, Australian Shepherds, etc.) require a 25% dose reduction if heterozygous, and a 30-50% reduction if homozygous.
- Giant Breeds & Sight Hounds: Extremely sensitive; require lower doses.
- Terriers: May be somewhat resistant to effects.
Administration: Give IV injections slowly. Allow at least 15 minutes for onset of action. Never inject intra-arterially in horses.
Behavioral: Use cautiously as a restraining agent in aggressive dogs; it may make the animal more prone to startle and react to noises.
Other: May cause regurgitation of ruminal contents in cattle during general anesthesia induction.
Drug interactions
Possible increased risk for hypothermia
May cause reduced GI absorption of oral phenothiazines
May cause reduced GI absorption of oral phenothiazines
May cause additive CNS depression if used with acepromazine
Acepromazine may impair the vasopressive action of dopamine
Acepromazine may reduce the effectiveness of emetics
Concomitant use can lead to unopposed beta-activity causing vasodilation and increased cardiac rate (epinephrine reversal)
May increase risks for extrapyramidal adverse effects
May enhance hypotensive effects; dosages of acepromazine are generally reduced when used with an opiate
Effects may be potentiated; do not give within one month of worming with these agents
Metabolism may be decreased if given concurrently
Activity may be enhanced by phenothiazines
Increased blood levels of both drugs may result
May cause additive cardiac depression
Additive CNS depression; doses of other anaesthetic drugs should be reduced when ACP is used for premedication
Unopposed beta activity causing severe vasodilation and tachycardia (due to ACP's alpha-adrenergic blockade)
Reduced GI absorption of oral phenothiazines
Monitoring
- Cardiac rate, rhythm, and blood pressure (especially in compromised patients)
- Degree of tranquilization and sedation
- Male horses: Monitor to ensure the penis retracts and is not injured
- Body temperature (especially if ambient temperature is very hot or cold)
Pharmacokinetics
Half-life
Absorption
Onset of action is fairly slow, requiring up to 15 minutes following IV administration, with peak effects seen in 30-60 minutes.
Distribution
Fairly high volume of distribution (6.6 L/kg in horses), and is more than 99% protein bound.
Metabolism
Metabolized in the liver.
Elimination
Both conjugated and unconjugated metabolites are eliminated in the urine. Metabolites may be found in equine urine up to 96 hours after dosing.
Overdose
The LD50 in mice is 61 mg/kg IV and 257 mg/kg PO. Dogs have survived oral dosages up to 220 mg/kg, but overdoses can cause serious hypotension, CNS depression, pulmonary edema, and hyperemia.
Clinical Signs of Toxicity:
- Dogs: Ataxia, sedation, lethargy, depression, protrusion of the third eyelid, somnolence, bradycardia, and recumbency.
- Cats: Sedation, ataxia, lethargy, protrusion of the third eyelid, and depression.
Treatment:
- Because of relatively low toxicity, most overdoses are handled by monitoring and symptomatic treatment.
- Massive oral overdoses should be treated by emptying the gut if possible.
- Hypotension: Should not be treated initially with fluids. If fluids fail to maintain BP, use alpha-adrenergic pressor agents (e.g., phenylephrine). Note: Avoid epinephrine due to the risk of "epinephrine reversal" causing further vasodilation.
- Seizures: May be controlled with barbiturates or diazepam.
- CNS Depression: Doxapram has been suggested as an antagonist to the CNS depressant effects.
Available products
Formulations
- Injection: 10 mg/mL
- Tablets: 5 mg, 10 mg, 25 mg
Veterinary
- Acepromazine Maleate for Injection: 10 mg/mL in 50 mL vials (PromAce, generic)
- Acepromazine Maleate Tablets: 5 mg, 10 mg & 25 mg (PromAce, generic)
Regulatory status
Classified as POM-V (Prescription Only Medicine - Veterinarian)
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store protected from light. Tablets should be stored in tight containers. Acepromazine injection should be kept from freezing. Stable and efficacious for at least 180 days after mixing with ketamine and xylazine if stored at room temperature in the dark.
Client information
- Urine Discoloration: This medication may temporarily discolor your pet's urine to a pink or red-brown color; this is a normal side effect and is not a cause for alarm.
- Not a Pain Reliever: Acepromazine provides sedation but does not relieve pain. If your pet is undergoing a painful procedure, other medications will be needed.
- Keep Environment Quiet: Even though your pet looks sleepy, they can still be startled by loud noises or sudden movements and may react unpredictably. Keep them in a quiet, calm environment while the drug wears off.
- Third Eyelid: You may notice your pet's "third eyelid" (a membrane in the inner corner of the eye) covering part of the eye. This is normal and will resolve as the medication wears off.
- Regulatory: FDA-approved for use in dogs, cats, and horses not intended for food.
VetSheet drug reference is intended for licensed veterinary professionals as a clinical decision-support aid, not a substitute for professional judgement or the manufacturer’s current label.