Naloxone Hydrochloride

Opioid Antagonist Opioid Receptor Antagonist

Dosage & Administration Guidelines

Species Route Dose Frequency Duration & Clinical Notes
Dog IV, IM, SC 0.01-0.04 mg/kg (for reversal of opioid effects); 0.04 mg/kg (for overdose, may repeat) As needed; may repeat every 2-3 minutes if no response, or every 20-60 minutes if renarcotization occurs Duration: Short-term; monitor for renarcotization
Notes: Titrate to effect. For reversal of anesthesia, use lower end of dose range to avoid acute withdrawal and pain.
Cat IV, IM, SC 0.01-0.04 mg/kg (for reversal of opioid effects); 0.04 mg/kg (for overdose, may repeat) As needed; may repeat every 2-3 minutes if no response, or every 20-60 minutes if renarcotization occurs Duration: Short-term; monitor for renarcotization
Notes: Titrate to effect. For reversal of anesthesia, use lower end of dose range to avoid acute withdrawal and pain.
Horse IV 0.01-0.02 mg/kg (for reversal of opioid effects); 0.04 mg/kg (for overdose) As needed; may repeat every 2-3 minutes if no response Duration: Short-term; monitor for renarcotization
Notes: Use with caution in horses with colic; may cause acute withdrawal and gastrointestinal hypermotility.
Cattle IV, IM, SC 0.01-0.04 mg/kg (for reversal of opioid effects); 0.04 mg/kg (for overdose) As needed; may repeat every 2-3 minutes if no response Duration: Short-term; monitor for renarcotization
Notes: For food animals, observe withdrawal times.
Small Ruminants (sheep, goats) IV, IM, SC 0.01-0.04 mg/kg (for reversal of opioid effects); 0.04 mg/kg (for overdose) As needed; may repeat every 2-3 minutes if no response Duration: Short-term; monitor for renarcotization
Notes: For food animals, observe withdrawal times.
Rabbit IV, IM, SC 0.01-0.05 mg/kg (for reversal of opioid effects); 0.05 mg/kg (for overdose) As needed; may repeat every 2-3 minutes if no response Duration: Short-term; monitor for renarcotization
Notes: Use lower doses for reversal of anesthesia.
Birds (poultry, pet birds) IV, IM 0.01-0.05 mg/kg (for reversal of opioid effects); 0.05 mg/kg (for overdose) As needed; may repeat every 2-3 minutes if no response Duration: Short-term; monitor for renarcotization
Notes: Use with caution; birds may be sensitive to acute withdrawal.
Exotic (reptiles, small mammals) IV, IM, SC 0.01-0.05 mg/kg (for reversal of opioid effects); 0.05 mg/kg (for overdose) As needed; may repeat every 2-3 minutes if no response Duration: Short-term; monitor for renarcotization
Notes: Dose based on clinical response; use lower end for reversal.

Clinical Indications & Species Uses

General Indications
  • Reversal of opioid-induced respiratory depression
  • Treatment of opioid overdose
  • Reversal of opioid effects after anesthesia or analgesia
  • Diagnostic aid for suspected opioid toxicity
Dog (Canine)
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose
  • Reversal of opioid effects after anesthesia or analgesia
  • Diagnostic aid for suspected opioid toxicity
Cat (Feline)
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose
  • Reversal of opioid effects after anesthesia or analgesia
  • Diagnostic aid for suspected opioid toxicity
Horse (Equine)
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose
  • Reversal of opioid effects after anesthesia or analgesia
Cattle (Bovine)
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose
  • Reversal of opioid effects after anesthesia or analgesia
Small Ruminants (Sheep / Goat)
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose
  • Reversal of opioid effects after anesthesia or analgesia
Rabbit & Small Mammals
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose
  • Reversal of opioid effects after anesthesia or analgesia
Avian & Poultry
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose
Exotic & Other Species
  • Reversal of opioid-induced respiratory depression and sedation
  • Treatment of opioid overdose

Pharmacology & Mechanism of Action

Drug Class: Opioid Antagonist | Pharmacological Group: Opioid Receptor Antagonist

Mechanism of Action: Naloxone is a competitive antagonist at opioid receptors (mu, kappa, and delta) in the central and peripheral nervous systems. It has the highest affinity for the mu receptor, which mediates most of the analgesic and euphoric effects of opioids. By binding to these receptors without activating them, naloxone displaces opioid agonists and reverses their effects, including respiratory depression, sedation, hypotension, and analgesia. It is a pure antagonist with no intrinsic opioid activity.

Pharmacodynamics: Naloxone rapidly reverses opioid-induced effects. Its onset of action is within 1-2 minutes after intravenous administration and 2-5 minutes after subcutaneous or intramuscular injection. The duration of action is typically 20-90 minutes, which may be shorter than that of many opioids, leading to renarcotization. Naloxone does not produce tolerance or dependence. In the absence of opioids, it has no significant pharmacologic effects.

⚑ Pharmacokinetics Summary

Absorption: Naloxone is well absorbed after parenteral administration. Oral bioavailability is very low (<2%) due to extensive first-pass metabolism, so it is not used orally. After IV administration, onset is immediate; after SC or IM, onset is within 2-5 minutes.
Distribution: Naloxone is rapidly distributed throughout the body. It crosses the blood-brain barrier readily, allowing central opioid receptor antagonism. It also crosses the placenta. Volume of distribution is approximately 2-3 L/kg in dogs.
Metabolism: Naloxone is primarily metabolized in the liver via conjugation with glucuronic acid to form naloxone-3-glucuronide, an inactive metabolite. Minor metabolic pathways include N-dealkylation and reduction.
Excretion: Naloxone and its metabolites are excreted primarily in the urine. In dogs, approximately 70% of a dose is excreted in the urine within 24 hours, with a small amount in feces. Biliary excretion may also occur.
Half-Life: Dog: 0.5-1 hour; Cat: approximately 0.5-1 hour; Horse: approximately 0.5-1 hour; Cattle: approximately 0.5-1 hour.
Bioavailability: Oral bioavailability is very low (<2%). Parenteral routes (IV, IM, SC) provide 100% bioavailability.
Protein Binding: Approximately 45-50% bound to plasma proteins in dogs and humans.

Available Formulations & Strengths

Injectable Solution 0.4 mg/mL, 1 mg/mL (IV, IM, SC)
Injectable Solution (veterinary specific) 0.5 mg/mL (some veterinary products) (IV, IM, SC)

Contraindications & Clinical Warnings

Contraindications:
  • Known hypersensitivity to naloxone or any component of the formulation
  • Use in patients with known opioid dependence (may precipitate acute withdrawal)
  • Do not use as a diagnostic agent in patients with suspected opioid dependence unless emergency
Warnings & Clinical Precautions:
  • May precipitate acute opioid withdrawal in animals with physical dependence, causing agitation, tachycardia, hypertension, and gastrointestinal signs.
  • Duration of action may be shorter than that of the opioid agonist; monitor for renarcotization and repeat doses as needed.
  • Use with caution in animals with cardiovascular disease, as reversal may cause rapid hemodynamic changes.
  • In pregnant animals, use only if clearly needed; naloxone crosses the placenta and may precipitate withdrawal in the fetus.
  • For food animals, observe withdrawal times to ensure food safety.
  • Do not mix with other drugs in the same syringe unless compatibility is known.

Adverse Effects & Reactions

Common:

  • Vomiting
  • Tachycardia
  • Hypertension
  • Tremors
  • Agitation

Serious / Severe:

  • Acute opioid withdrawal syndrome (severe agitation, seizures, cardiac arrhythmias)
  • Pulmonary edema (rare but reported in humans; monitor in animals)
  • Cardiac arrest (in severe cases)

Rare:

  • Hypersensitivity reactions
  • Seizures (especially in neonates or with rapid IV administration)

Key Drug Interactions

Interacting Drug / Class Clinical Effect & Mechanism Severity
Opioid agonists (e.g., morphine, fentanyl, butorphanol) Naloxone antagonizes the effects of opioid agonists, reversing analgesia and respiratory depression. High
Opioid agonist-antagonists (e.g., buprenorphine, pentazocine) Naloxone may partially reverse effects; buprenorphine has high receptor affinity and may be difficult to reverse completely. Moderate
Clonidine Naloxone may reduce the antihypertensive effects of clonidine. Mild
Cardiovascular drugs (e.g., beta-blockers, calcium channel blockers) Naloxone may cause sudden catecholamine release, leading to arrhythmias; use with caution. Moderate

Overdose & Toxicity Management

Signs of Toxicity:

  • In animals without opioid exposure, naloxone has minimal effects; overdose may cause transient hypertension, tachycardia, and agitation.
  • In opioid-dependent animals, overdose may precipitate severe withdrawal signs: vomiting, diarrhea, tremors, seizures, and cardiovascular collapse.

Emergency Treatment Protocol: Treatment is symptomatic and supportive. Monitor vital signs and cardiac function. For withdrawal signs, administer sedatives (e.g., benzodiazepines) as needed. In severe cases, consider vasopressors for hypotension. Since naloxone has a short half-life, effects are usually transient; supportive care is the mainstay.

Food Animal Withdrawal Times

πŸ₯© Meat: 0 daysπŸ₯› Milk: 0 daysπŸ₯š Eggs: 0 days

Naloxone is not approved for food animals; however, due to its short half-life and rapid elimination, withdrawal times are typically minimal. For extra-label use in food animals, consult a veterinarian and follow regulatory guidelines; a withdrawal time of 0 days is often cited, but it is prudent to allow 24 hours for safety.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature 20-25Β°C (68-77Β°F); protect from light.

Light Sensitivity: Light-sensitive β€” protect from direct exposure.

Handling & Special Conditions: Do not freeze. Keep in original container. Protect from light.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Not FDA-approved for veterinary species; approved for human use. Veterinary use is extra-label.

Extra-Label (Off-Label) Use: In the US, naloxone is not FDA-approved for veterinary use, but it is commonly used extra-label under AMDUCA. For food animals, extra-label use requires a valid veterinarian-client-patient relationship and observance of withdrawal times.

Clinical Pearls & Practice Notes

πŸ’‘ Clinical Insights: Naloxone is an essential emergency drug in veterinary practice for reversing opioid-induced respiratory depression and overdose. It is particularly useful in anesthesia protocols where opioids are used. Because its duration of action is shorter than many opioids, repeated dosing or continuous rate infusion may be necessary, especially with long-acting opioids like buprenorphine. Always titrate to effect to avoid acute withdrawal and pain. In cases of opioid overdose, naloxone should be administered immediately, and supportive care (oxygen, ventilation) should be provided. For food animals, ensure compliance with withdrawal times. Naloxone is not a substitute for supportive care and should be used as part of a comprehensive treatment plan.

References & Literature

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