Naloxone HCl: veterinary dose and monograph

At a glance

Drug class

Veterinary drug

Also known as

Narcan

Species with doses

Dogs, Cats, Horses and Rabbits

General dose range

0.01–0.04 mg/kg IV titrate to effect (repeat q30 min) — check the species tables for the indication

Routes

IV

Last reviewed

1 October 2026

Indications

• Reversal of opioid-induced respiratory depression
• Reversal of post-op opioid dysphoria
• Neonate / foal apnoea after maternal opioid analgesia (caesarean)
• Buprenorphine overdose (higher doses needed due to tight receptor binding)
• Diagnostic — confirms opioid involvement in mystery sedation

Naloxone HCl 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.

Dogs

• Opioid reversal — titrate to respiratory effort: Papich 5e: 0.01–0.04 mg/kg IV, IM or SC as needed; a full antagonist dose is 0.04 mg/kg. Plumb’s p.873: 0.01–0.02 mg/kg IM, IV or SC (Trim 2008); 0.04 mg/kg (label). Naloxone is shorter-acting than most opioids — watch for re-narcotisation and redose.
• Dysphoria from full-mu opioid: Plumb’s p.873 (Dyson 2008): 4 µg/kg diluted to 10 mL and given in 1 mL increments every minute to effect. Papich 5e: 1 mL every 30 s of a 0.04 mg/mL dilution as needed. Stops the dysphoria while preserving some analgesia.

Cats

• Opioid reversal: Papich 5e and Plumb’s p.873 give dogs and cats the same range: 0.01–0.04 mg/kg IV, IM or SC (full antagonist 0.04 mg/kg). Neonates after caesarean: one drop of 0.4 mg/mL under the tongue (Dyson 2008).

Horses

• Opioid reversal (esp. butorphanol / morphine sedation): Plumb’s p.873: 0.01–0.022 mg/kg to reverse sedative and excitatory effects of opioid agonists (Clark & Becht 1987); 0.01 mg/kg IV limits locomotor activity (Muir 1987). Papich 5e: 0.02–0.04 mg/kg IV — duration of effect only about 20 min. ARCI Class 3.

Pigs

• No reference dose for this species: The previous 0.01–0.04 mg/kg row for pigs had no source; neither Papich 5e nor Plumb’s gives a pig naloxone dose.

Rabbits

• Opioid reversal in rabbits: Plumb’s p.873 (Ivey & Morrisey 2000): rabbits 0.005–0.1 mg/kg IM or IV. Rodents 0.01–0.1 mg/kg SC or IP (Adamcak & Otten 2000).

Contraindications

Known hypersensitivity. Caution: full reversal of analgesia in animals with severe pain is contraindicated — titrate to respiratory effort only. Withdrawal seizures in opioid-dependent patients (rare in veterinary practice).

Species-specific warnings

Dogs: Titrate to respiratory effort — full reversal causes pain crisis. Buprenorphine needs higher repeated doses.

Rabbits: Rabbits metabolise opioids fast — repeat naloxone may be needed within 20–30 min.

Adverse effects

• Acute pain crisis (rapid full reversal of analgesia)
• Tachycardia / hypertension
• Tremor / hyperalgesia
• Vomiting (sudden return of GI motility)

Drug interactions

• Reverses ALL opioid effects — including analgesia (titrate carefully to respiratory effort only)
• No clinically significant non-opioid interactions

Pregnancy and lactation

Safe — used in neonate / foal apnoea after maternal caesarean. FDA Category B (human).

Monitoring

• Respiratory rate / SpO2 — primary endpoint
• Repeated assessment every 30–60 min — opioid often outlasts naloxone
• Pain score — if reversed analgesia, redose opioid at low dose
• Heart rate / blood pressure (acute reversal can cause tachycardia / hypertension)

Toxicity and overdose

Management: No specific toxicity at clinical doses. Concern is from acute pain crisis if over-reversed — re-administer opioid at half-original dose for analgesia.

Clinical pearls

• Post-op opioid dysphoria: 1–5 µg/kg IV partial reversal clears dysphoria while preserving analgesia — KEY pearl for surgery recovery
• Foal born from caesarean with maternal morphine on board: 0.02 mg/kg IV in umbilical vein → instant respiratory response
• Buprenorphine overdose needs HIGHER repeated naloxone doses (0.04 mg/kg IV q30 min × multiple doses) — buprenorphine tightly binds receptors
• Rabbit overdose: 0.05 mg/kg IV; rabbits metabolise fast so opioid AND naloxone clear quickly
• Always have naloxone drawn up and on the anaesthesia tray during any opioid-based surgery

Mechanism of action

Pure competitive antagonist at mu (preferred), kappa, and delta opioid receptors. Displaces opioid agonists, reversing their effects within 1–2 min IV. Onset 1–2 min, peak 5 min, duration 30–60 min. No intrinsic agonist activity → no respiratory depression of its own at any dose. Repeated dosing or CRI (5–20 µg/kg/h) often needed for long-acting opioids (morphine, methadone) or buprenorphine.

Formulations and products

• Naloxone 0.4 mg/mL injection
• Naloxone 1 mg/mL injection

Storage

15–25 °C, protect from light.

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.

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Frequently asked questions