Azaperone: veterinary dose and monograph

At a glance

Drug class

Sedative / anaesthetic

Also known as

Stresnil, Azaperone

Species with doses

Pigs

General dose range

1–8 mg/kg IM single dose — check the species tables for the indication

Routes

IM

Last reviewed

1 October 2026

Indications

• Prevention of aggression/fighting when mixing or regrouping pigs
• Promotion of sow acceptance of piglets / reduction of savaging
• Sedation/tranquillisation for transport, handling and minor procedures in pigs
• Premedication / restraint (with ketamine); wildlife immobilisation

Azaperone dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Pigs

• Aggression on mixing / sow aggression: Plumb’s p.133: 2 mg/kg (1 mL per 20 kg) deep IM directly behind the ear (UK label); 2.2 mg/kg deep IM for mixing feeder/weanling pigs (former US label). Keep pigs undisturbed during the ~20 min onset. Follow the local label withdrawal.
• Stress / transport / obstetrics / premedication: Plumb’s p.133 (UK label, IM behind the ear): stress 1–2 mg/kg; boar transport 1 mg/kg; weaner transport 0.4–2 mg/kg; obstetrics 1 mg/kg; premedication 1–2 mg/kg. Neither Papich 5e nor Plumb’s gives the higher 4–8 mg/kg restraint doses. Follow the local label withdrawal.

Wildlife

• No reference dose for this species: Plumb’s mentions that azaperone is part of the BAM (butorphanol–azaperone–medetomidine) combination for cervids but gives no dose (and notes it may add hypoxia risk); Papich 5e has no monograph. Use a wildlife immobilisation reference.

Contraindications

HORSES, especially stallions (hypotension; persistent penile prolapse/paralysis). Severe cardiovascular compromise/shock (alpha-blockade hypotension). Use as a sole agent for painful procedures (limited analgesia). Excitement/noise during onset (handle quietly). Known hypersensitivity. Observe meat withdrawal in pigs.

Species-specific warnings

Horses: Contraindicated — azaperone can cause severe hypotension and persistent penile prolapse/paraphimosis in horses (especially stallions).

Adverse effects

• Hypotension (alpha-adrenergic blockade)
• Sedation/ataxia; occasional excitement during onset (keep quiet)
• Hypothermia; salivation
• Penile prolapse (a hazard chiefly in horses — contraindicated there)

Drug interactions

• Other CNS depressants/anaesthetics (ketamine): additive sedation (often combined deliberately)
• Other hypotensive agents: additive hypotension
• Adrenaline: alpha-blockade can produce paradoxical hypotension (avoid adrenaline reversal)

Pregnancy and lactation

Used in sows (including to aid piglet acceptance); follow label. Avoid unnecessary use late in pregnancy.

Monitoring

• Sedation level and aggression control (mixing) — keep the group quiet during onset
• Blood pressure/perfusion (hypotension)
• Temperature (hypothermia)
• Meat withdrawal compliance

Toxicity and overdose

Overdose causes excessive sedation, hypotension, hypothermia and ataxia. In horses (where it is contraindicated) it can cause severe hypotension and persistent penile prolapse/paraphimosis. Otherwise a reasonable margin in pigs.

Management: No specific antidote. Supportive — IV fluids for hypotension (do NOT use adrenaline, which can worsen hypotension via unopposed beta effects given the alpha-blockade; use a direct alpha-agonist like phenylephrine if a pressor is needed), keep warm and quiet. Effects resolve with time.

Clinical pearls

• The classic "mixing pigs" drug — IM azaperone calms regrouped/unfamiliar pigs and reduces fighting, and helps sows accept piglets; keep the group quiet during the ~20-minute onset
• NOT for horses — risk of severe hypotension and penile prolapse/paralysis (especially stallions)
• Provides tranquillisation, not analgesia — combine with ketamine/analgesics for painful procedures
• If a pressor is needed for hypotension, use a direct alpha-agonist (phenylephrine), not adrenaline (alpha-blockade)

Mechanism of action

A butyrophenone that antagonises central dopamine (D2) receptors, producing neuroleptic tranquillisation, reduced motor/aggressive activity and an anti-emetic effect, with limited analgesia. Peripheral alpha-adrenergic blockade causes vasodilation/hypotension (and, in horses, smooth-muscle relaxation leading to penile prolapse). The dopaminergic calming underlies its anti-aggression use when pigs are mixed.

Formulations and products

• Injection 40 mg/mL (Stresnil)
• Stresnil (Elanco (Janssen)) — 40 mg/mL, IM injection

Storage

Injection: 15–30 °C, protect from light; do not freeze.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other sedatives and anaesthetics

• Acepromazine
• Alfaxalone
• Detomidine
• Dexmedetomidine
• Diazepam
• Etomidate
• Guaifenesin (GGE)
• Isoflurane

Frequently asked questions