Pentobarbital Sodium — Veterinary Vademecum Drug Reference

Dosage & Administration Guidelines

Species	Route	Dose	Frequency	Duration & Clinical Notes
Dog	IV	Anesthesia: 20-30 mg/kg (to effect); Anticonvulsant: 3-15 mg/kg IV slowly to effect; Euthanasia: 100-150 mg/kg IV	Single dose for anesthesia or euthanasia; for seizures, may repeat as needed	Duration: Anesthesia: 15-30 minutes; Euthanasia: immediate Notes: Administer slowly to avoid respiratory arrest. For euthanasia, use a concentrated solution (e.g., 390 mg/mL) to ensure rapid effect.
Cat	IV	Anesthesia: 20-30 mg/kg (to effect); Anticonvulsant: 3-15 mg/kg IV slowly to effect; Euthanasia: 100-150 mg/kg IV	Single dose for anesthesia or euthanasia; for seizures, may repeat as needed	Duration: Anesthesia: 15-30 minutes; Euthanasia: immediate Notes: Cats are more sensitive to barbiturates; use lower doses and monitor carefully.
Horse	IV	Anesthesia: 5-15 mg/kg IV (usually in combination with other agents); Euthanasia: 80-100 mg/kg IV	Single dose	Duration: Anesthesia: 10-20 minutes Notes: Recovery can be prolonged and rough; often used for induction before inhalant anesthesia.
Cattle	IV	Anesthesia: 10-20 mg/kg IV (rarely used); Euthanasia: 100 mg/kg IV	Single dose	Duration: Anesthesia: 15-30 minutes Notes: Not commonly used for anesthesia due to prolonged recovery and risk of regurgitation. For euthanasia, ensure proper restraint.
Small Ruminants (Sheep, Goats)	IV	Anesthesia: 10-20 mg/kg IV (rarely used); Euthanasia: 100 mg/kg IV	Single dose	Duration: Anesthesia: 15-30 minutes Notes: Similar to cattle; not commonly used for anesthesia.
Rabbit	IV	Anesthesia: 20-40 mg/kg IV (rarely used); Euthanasia: 100-150 mg/kg IV	Single dose	Duration: Anesthesia: 15-30 minutes Notes: Rabbits are sensitive to barbiturates; use with caution. Euthanasia is often performed with IV administration.
Birds/Poultry	IV	Euthanasia: 100 mg/kg IV (if accessible)	Single dose	Duration: Immediate Notes: Not approved for food birds in many countries. Alternative methods may be preferred.
Exotic/Other	IV, IP, IC	Euthanasia: 100-150 mg/kg IV or IP (dose varies by species)	Single dose	Duration: Immediate Notes: For reptiles, intracardiac injection may be used after sedation. Consult species-specific references.

Clinical Indications & Species Uses

General Indications

Anesthesia induction
Status epilepticus (as a last resort)
Euthanasia

Dog (Canine)

Induction of anesthesia
Anticonvulsant for status epilepticus (refractory to other agents)
Euthanasia (in combination with other agents)

Cat (Feline)

Induction of anesthesia
Anticonvulsant for status epilepticus (refractory to other agents)
Euthanasia (in combination with other agents)

Horse (Equine)

Induction of anesthesia (often in combination with other agents)
Euthanasia

Cattle (Bovine)

Induction of anesthesia (rarely used due to prolonged recovery)
Euthanasia

Small Ruminants (Sheep / Goat)

Induction of anesthesia (rarely used)
Euthanasia

Rabbit & Small Mammals

Induction of anesthesia (rarely used)
Euthanasia

Avian & Poultry

Euthanasia (in some countries, not approved in food birds)

Exotic & Other Species

Euthanasia in various exotic species (e.g., reptiles, small mammals)

Pharmacology & Mechanism of Action

Drug Class: Barbiturate | Pharmacological Group: Anesthetic, Anticonvulsant, Euthanasia Agent

Mechanism of Action: Pentobarbital is a short-acting barbiturate that acts as a central nervous system (CNS) depressant. It enhances the inhibitory neurotransmitter gamma-aminobutyric acid (GABA) at GABA-A receptors, increasing the duration of chloride channel opening, leading to hyperpolarization of neurons and inhibition of neuronal firing. This results in dose-dependent sedation, hypnosis, anesthesia, and at high doses, respiratory and cardiovascular depression leading to death.

Pharmacodynamics: Pentobarbital produces a dose-dependent depression of the CNS. At low doses, it has sedative and anticonvulsant effects; at higher doses, it induces general anesthesia. It has minimal analgesic properties and may cause respiratory depression, hypotension, and decreased cardiac output. It also decreases cerebral metabolic rate and intracranial pressure. At euthanasia doses, it rapidly induces deep anesthesia followed by respiratory and cardiac arrest.

⚡ Pharmacokinetics Summary

Absorption: Rapidly absorbed after oral administration, but due to first-pass metabolism, oral bioavailability is variable. Intravenous administration provides immediate onset of action. Intraperitoneal and intramuscular routes are also used in small animals.

Distribution: Widely distributed throughout the body, with high affinity for lipid-rich tissues such as the brain and adipose tissue. It crosses the placenta and is distributed into milk. Protein binding is approximately 40-60%.

Metabolism: Extensively metabolized in the liver via hydroxylation and oxidation, primarily by hepatic microsomal enzymes. Metabolites are inactive and excreted in urine.

Excretion: Metabolites and a small amount of unchanged drug are excreted by the kidneys. In dogs, approximately 25% is excreted unchanged in urine. Fecal excretion is minimal.

Half-Life: Dogs: 8-12 hours; Cats: 8-12 hours; Horses: 2-4 hours; Cattle: 4-6 hours (estimated).

Bioavailability: Oral bioavailability is variable (70-90%) due to first-pass metabolism; IV administration results in 100% bioavailability.

Protein Binding: Approximately 40-60% bound to plasma proteins.

Available Formulations & Strengths

Injectable Solution 50 mg/mL, 100 mg/mL, 390 mg/mL (euthanasia solutions) (IV, IP, IC)

Oral Tablet (rarely used) 30 mg, 60 mg, 100 mg (PO)

Contraindications & Clinical Warnings

Contraindications:

Known hypersensitivity to barbiturates
Severe hepatic dysfunction
Severe respiratory insufficiency
Severe cardiovascular instability (except for euthanasia)
Porphyria (barbiturates can precipitate acute attacks)
Use in animals intended for food (unless allowed for euthanasia with appropriate withdrawal times)

Warnings & Clinical Precautions:

Administer IV slowly to avoid respiratory depression and apnea.
Have resuscitation equipment available when used for anesthesia.
May cause tissue necrosis if injected perivascularly; use a central vein if possible.
Use with caution in debilitated, geriatric, or pediatric animals; reduce dose.
In horses, recovery may be violent; ensure adequate padding and supervision.
For euthanasia, ensure the animal is unconscious before confirming death; use a secondary method (e.g., exsanguination, KCl) to ensure death.
Pentobarbital is a controlled substance; store securely and keep records.
In food animals, observe withdrawal times; extra-label use is prohibited in some countries.

Adverse Effects & Reactions

Common:

Respiratory depression
Hypotension
Cardiac arrhythmias
Prolonged recovery (especially in horses)
Excitement during induction (if too slow)
Tissue irritation at injection site

Serious / Severe:

Apnea
Cardiovascular collapse
Pulmonary edema
Laryngospasm
Anaphylaxis (rare)
Death (at high doses)

Rare:

Hepatotoxicity
Blood dyscrasias
Hypothermia
Paradoxical excitement

Key Drug Interactions

Interacting Drug / Class	Clinical Effect & Mechanism	Severity
Other CNS depressants (e.g., opioids, benzodiazepines, inhalant anesthetics)	Additive CNS and respiratory depression; reduce doses of both agents.	High
Chloramphenicol	Inhibits hepatic metabolism of pentobarbital, increasing its effects and duration.	Moderate
Corticosteroids	May induce hepatic enzymes, reducing pentobarbital efficacy.	Mild
Phenytoin	May alter metabolism of both drugs; monitor for toxicity.	Moderate
Antihistamines	Additive CNS depression.	Mild

Overdose & Toxicity Management

Signs of Toxicity:

Severe respiratory depression
Apnea
Hypotension
Cardiac arrhythmias
Coma
Death

Emergency Treatment Protocol: There is no specific antidote. Treatment is supportive: maintain airway, provide artificial ventilation, administer IV fluids and vasopressors (e.g., dopamine, norepinephrine) for hypotension, and manage cardiac arrhythmias. In cases of recent oral ingestion, gastric lavage and activated charcoal may be considered. For euthanasia overdose, death is expected.

Food Animal Withdrawal Times

🥩 Meat: 28 days🥛 Milk: 7 days

Pentobarbital is not approved for use in food animals in many countries. If used for euthanasia, the carcass must be properly disposed of and not enter the food chain. In the US, extra-label use in food animals is prohibited. Withdrawal times are not established; consult regulatory authorities.

Storage, Handling & Regulatory Information

Storage Temperature: Store at controlled room temperature (20-25°C, excursions 15-30°C).

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

Handling & Special Conditions: Protect from light. Keep tightly closed. Store in a secure, locked area due to controlled substance status.

Dispensing Status: Prescription Required (Rx Only)

Approval Status: Approved for use in dogs and cats for anesthesia and euthanasia (e.g., Beuthanasia-D Special). Not approved for food animals.

Extra-Label (Off-Label) Use: In the US, extra-label use of pentobarbital in food animals is prohibited by the FDA. In non-food animals, extra-label use is permitted under AMDUCA with appropriate veterinary oversight. In the EU, similar restrictions apply.

Clinical Pearls & Practice Notes

💡 Clinical Insights: Pentobarbital is primarily used for euthanasia in veterinary practice due to its rapid and humane action. As an anesthetic, it is less commonly used because of prolonged recovery and poor analgesic properties. It may be used for refractory status epilepticus when other anticonvulsants fail. Due to its controlled substance status, strict record-keeping is required. For euthanasia, always confirm death by auscultation of heart and lungs, and consider a secondary method to ensure death. In horses, recovery from anesthesia can be dangerous; use only when necessary. In food animals, pentobarbital should never be used unless explicitly allowed for euthanasia with proper carcass disposal.

References & Literature

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