Methohexital
Methohexital sodium
Also known as: Brevital · Brevimytal · Brietal · compound 25398 · enallynymalnatrium · methohexitone sodium
Reviewed by the VetSheet Veterinary TeamUpdated Apr 5, 2026Evidence-based veterinary reference
Audited v13 dosing evidence
Reviewed non-calculator evidenceReviewed non-calculator evidence (3)
Evidence only — not for automatic calculation
Recovery time of red-sided garter snakes at 21°C (70°F), 125 min; 26°C (79°F), 86 min; 31°C (88°F), 64 min; thinner snakes had longer recovery times; if within 5 wk of parturition, mean recovery time 2 × as long as nongravid; time postfeeding had no effect at 1, 3, 10 days266
TABLE 127.5. Agent: Methohexital (Brevital, Lilly). Dosage: —. Species/Comments: Recovery time of red-sided garter snakes at 21°C (70°F), 125 min; 26°C (79°F), 86 min; 31°C (88°F), 64 min; thinner snakes had longer recovery times; if within 5 wk of parturition, mean recovery time 2 × as long as nongravid; time postfeeding had no effect at 1, 3, 10 days266.
Evidence only — not for automatic calculation
Most species/induction, 5–30 min; recovery, 1–5 hr; use at 0.125%–0.5% concentration; much species variability; decrease dose 20%–30% for young animals; avoid use in debilitated animals
TABLE 127.5. Agent: Methohexital (Brevital, Lilly). Dosage: 5–20 mg/kg SC,19 IV89. Species/Comments: Most species/induction, 5–30 min; recovery, 1–5 hr; use at 0.125%–0.5% concentration; much species variability; decrease dose 20%–30% for young animals; avoid use in debilitated animals.
Evidence only — not for automatic calculation
Colubrids/induction, ≥ 22 min; recovery, 2–5 hr; does not produce soft-tissue irritation seen with other barbiturates; may need to adjust dosage in obese snakes
TABLE 127.5. Agent: Methohexital (Brevital, Lilly). Dosage: 9–10 mg/kg SC,243 ICe. Species/Comments: Colubrids/induction, ≥ 22 min; recovery, 2–5 hr; does not produce soft-tissue irritation seen with other barbiturates; may need to adjust dosage in obese snakes.
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Methohexital is an ultra-short-acting methylated oxybarbiturate anesthetic agent. While largely replaced by propofol in modern veterinary medicine, it retains niche utility, particularly in sight hounds (e.g., Greyhounds) because its termination of effect relies on rapid hepatic metabolism rather than redistribution to fat. It is also advantageous for rapid sequence intubation in patients with a full stomach, allowing an endotracheal tube to be placed rapidly before aspiration of vomitus can occur.
Clinical Pearls:
- It lacks analgesic and muscle relaxant properties.
- It is highly irritating to tissues; perivascular extravasation can cause severe localized necrosis.
- It is about twice as potent as thiopental with half the duration of action.
Mechanism of action
Methohexital produces dose-dependent CNS depression by depressing the reticular activating system in the brainstem.
- Mechanism: Binds to the GABA_A receptor complex → prolongs the opening of chloride channels → increases intracellular chloride influx → cellular hyperpolarization → profound inhibition of neuronal firing.
- Termination of Effect: Unlike thiobarbiturates, methohexital is rapidly metabolized by the liver and does not depend on redistribution to fat to reverse its effects.
Safety & warnings
Contraindications
- Absence of suitable veins for IV administration
- History of hypersensitivity reactions to barbiturates
- Status asthmaticus
- Cattle (due to unpredictable effects)
Adverse effects
- Apnea
- Hypotension
- Muscle tremors
- Seizures during recovery
- Rough recoveries (especially in dogs)
- Profound respiratory depression
- Tissue necrosis (if extravasated)
Precautions
WARNING: Strictly for IV use. Perivascular extravasation causes severe tissue necrosis. Extravasation injuries can be treated with multiple infiltrates of sterile normal saline and lidocaine for pain.
- Relative Contraindications: Seizure-prone animals, severe cardiovascular disease, preexisting ventricular arrhythmias, shock, increased intracranial pressure, myasthenia gravis, asthma, and conditions with prolonged hypnotic effects (e.g., severe hepatic disease, myxedema, severe anemia).
- Species Warnings: NOT recommended for use in cattle due to unpredictable effects.
- Administration: Repeated dosing or IV infusions are not recommended as recovery times can be significantly prolonged and increase the risk for complications.
Drug interactions
Additive CNS and respiratory depression; premedication is usually preferred to reduce methohexital dosage required for inductions and to decrease rough recoveries.
Monitoring
- Plane of anesthesia
- Respiratory rate and depth
- Cardiac rate, rhythm, and blood pressure
- CNS stimulation (seizures) upon recovery
Pharmacokinetics
Half-life
Absorption
Rapid onset of anesthesia (15-60 seconds) after IV injection.
Distribution
Distribution half-life is 5-6 minutes. Not dependent on redistribution to fat to reverse its effects.
Metabolism
Rapidly metabolized by the liver.
Elimination
No drug is detectable in the body 24 hours after administration. Recovery times in small animals average 30 minutes.
Overdose
Narrow Safety Margin: The lethal dose may only be 2-3 times the anesthetic dose.
- Clinical Signs: Profound respiratory depression, apnea, hypotension, and cardiovascular collapse.
- Treatment: Requires immediate mechanical ventilation and cardiovascular support. Postoperative seizures have been reported and can be treated with IV diazepam.
Available products
Formulations
- Powder for injection
Human-labeled
- Methohexital Sodium Powder for Injection: 500 mg & 2.5 grams in 50 mL multiple dose vials
Regulatory status
No regulatory data for: 🇺🇸 US · 🇪🇺 EU · 🇬🇧 UK · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store powder at room temperature (<25°C). Reconstitute preferably with sterile water for injection (D5W or 0.9% NaCl may be used for 0.2% concentrations). Do NOT use solutions with bacteriostatic agents. Incompatible with silicone (avoid silicone-treated rubber stoppers/syringes). Do NOT mix with acidic drugs (e.g., atropine, succinylcholine).
Client information
Methohexital is a fast-acting anesthetic used exclusively in the hospital setting to induce sleep before surgery or short procedures.
- Rapid Action: It works within seconds, allowing the veterinary team to quickly secure your pet's airway.
- Recovery: Some pets, especially dogs, may experience a "rough recovery" (tremors, excitement, or vocalization) as they wake up. The veterinary team will monitor them closely and may use other medications to smooth this process.
- Safety: Your pet's heart rate, breathing, and blood pressure will be continuously monitored while under the effects of this medication.
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.