Methohexital
Intravenous anaesthetics
Intravenous anaestheticsHigh alert
An error with this medicine can cause serious harm: double checks and protocols are used.
Ultra-short-acting barbiturate for anaesthesia induction, classically for electroconvulsive therapy. Contraindicated in porphyria.
Also called: Methohexital sodium, Methohexitone
Quick facts
- Group
- Intravenous anaesthetics
- Target
- GABA-A receptor
- Used for
- Intravenous induction
- Key effects
- Hiccups · Pain on injection · Nausea and vomiting
- Monitor
- Continuous pulse oximetry · ECG and blood pressure
- ATC
- N01AF01
No doses: the clinician sets them by the current guideline.
Mechanism of action
There is no structure with methohexital. The figure shows phenobarbital, another barbiturate, bound to the human α1β2γ2 GABA-A receptor with GABA.
Methohexital is an oxybarbiturate (it has no sulfur) that enhances and, at higher levels, directly activates GABA-A receptors, increasing chloride entry and depressing the brain. It reaches the brain within seconds and its effect after a single dose ends by redistribution to other tissues. It is cleared faster than thiopental and accumulates less, so recovery is quicker. It gives little analgesia and, unlike most anaesthetics, can increase seizure activity, which suits electroconvulsive therapy.
- Rapid entry into the brain after intravenous injection
- Potentiates GABA-A receptors: more chloride, neuronal depression
- Loss of consciousness; effect ended by redistribution
- Faster hepatic clearance than thiopental: quick recovery
Indications
- Intravenous induction of general anaesthesia and anaesthesia for short procedures with little painful stimulus
- Anaesthesia for electroconvulsive therapy, together with a neuromuscular blocker
- Rectal or intramuscular induction in children older than one month
Adverse effects
Common
- Hiccups, coughing and muscle twitching
- Pain on injection, more than with thiopental
- Transient hypotension and tachycardia
- Nausea and vomiting, emergence delirium
Contraindications
- Latent or manifest porphyria
- Known hypersensitivity to barbiturates
- Situations in which general anaesthesia is contraindicated
Key interactions
- Chronic barbiturates or phenytoin
- Reduced effectiveness of methohexital.
- Phenytoin, anticoagulants, corticosteroids and alcohol
- Barbiturates can change the metabolism of these drugs.
- Lactated Ringer's solution
- Incompatible as a diluent.
What is monitored
- Continuous pulse oximetry, airway and ventilation
- ECG and blood pressure
- Injection site: pain, blanching or swelling suggesting extravasation or arterial placement
- Seizure activity
Administration and safety
- Used only where respiratory and cardiac function are monitored continuously, with resuscitation drugs and airway equipment at hand.
- Reconstituted with compatible diluents (sterile water, dextrose or saline), never Lactated Ringer's; the alkaline solution is incompatible with many acidic drugs.
- Inject into a free-flowing vein; stop at once if pain, extravasation or arterial placement is suspected.
- Rectal and intramuscular routes are reserved for children, with the same monitoring.
Pregnancy and breastfeeding
Animal studies showed no developmental harm, and human data are lacking; prolonged or repeated anaesthetic exposure late in pregnancy or in young children raises concern for the developing brain.
Nursing care
- Before induction, ask about porphyria and previous reactions to barbiturates.
- Prepare oxygen, bag-mask, suction and intubation equipment.
- Watch the cannula site during injection for pain or blanching of the hand.
- After the procedure, monitor breathing and consciousness until fully awake.
Pharmacokinetics
- Distribution
- Very rapid uptake by the brain, then redistribution; it concentrates in fat less than thiobarbiturates.
- Metabolism
- Hepatic, by demethylation and side-chain oxidation.
- Elimination
- Kidney, by glomerular filtration of metabolites.
- Onset and duration
- Within seconds intravenously; slower by intramuscular or rectal routes in children.
Test yourself
Think of the answer, then tap the question to see it.
Why is methohexital a good choice for electroconvulsive therapy anaesthesia?
It is ultra-short acting and, unlike most anaesthetics, can increase seizure activity.
Which metabolic disease contraindicates methohexital?
Porphyria, latent or manifest, because barbiturates can trigger acute attacks.
What is the danger of intra-arterial injection of methohexital?
Thrombosis distal to the injection, with necrosis that may progress to gangrene.
Why do patients wake faster after methohexital than after thiopental?
It is cleared faster by the liver and concentrates less in fat, so it accumulates less.
Connections
← Back to the class: Intravenous anaesthetics
Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: DailyMed - METHOHEXITAL SODIUM injection (DailyMed (U.S. National Library of Medicine), 2026); RCSB PDB - 6X3W: Human GABAA receptor alpha1-beta2-gamma2 subtype in complex with GABA plus phenobarbital (RCSB Protein Data Bank, 2020); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
Spotted a mistake?We are always improving for the community. Tell us what is wrong and our team will review it.Report a mistake
Representative model, for educational purposes only.