Pharmacology · Intravenous anaesthetics
Thiopental !
Ultra-short-acting barbiturate that was the classic induction agent. It precipitates acute porphyria and damages tissue if injected into an artery.
Updated 2026-11-01
Also called: Thiopental sodium, Thiopentone
There is no structure with thiopental. The figure shows phenobarbital, another barbiturate, bound to the human α1β2γ2 GABA-A receptor with GABA.
Mechanism of action
Thiopental enhances the GABA-A receptor: it prolongs the GABA-activated opening of the chloride channel. Unconsciousness follows within seconds. A single dose ends by redistribution from the brain to muscle and fat; after repeated doses or infusions it accumulates and waking can take a long time. It reduces cerebral oxygen consumption, blood flow and intracranial pressure.
- Enhances the GABA-A receptor chloride channel
- Unconsciousness within seconds
- Redistribution to muscle and fat: waking after a single dose
- Accumulates with repeated doses: delayed waking
Pharmacokinetics
- Distribution
- Very lipid-soluble; large volume of distribution.
- Metabolism
- Hepatic to inactive metabolites; a small fraction becomes pentobarbital, which acts longer.
- Elimination
- Kidney, as metabolites.
Indications
- Induction of general anaesthesia
- Anaesthesia in patients with raised intracranial pressure, because it lowers intracranial blood flow and pressure
Adverse effects
Common
- Hypotension from venodilation
- Respiratory depression and apnoea
- Wheeze in asthmatics (histamine release)
- Cough, hiccups and tremor at induction
Contraindications
- Acute intermittent porphyria or variegate porphyria
- Hypersensitivity to barbiturates
Key interactions
- Drugs in acidic solution (rocuronium, vecuronium, atracurium and others)
- Thiopental, very alkaline, precipitates in the same line; wait until it has cleared the tubing before giving another drug.
- Opioids and other depressants
- Deeper apnoea and respiratory depression.
- Antihypertensives and beta-blockers
- More marked hypotension.
What is monitored
- Blood pressure, ECG and saturation
- Airway and ventilation
- Injection site (severe pain or pallor suggest intra-arterial injection)
Administration and safety
- Reconstituted as a very alkaline solution: do not mix with acidic drugs in the same syringe or line.
- Confirm that the line is venous: injection into an artery causes necrosis that threatens the limb.
- Extravasation irritates and damages tissue.
Nursing care
- Before: ask about personal or family history of porphyria.
- During: blood pressure and breathing; airway equipment ready.
- If there is severe pain, pallor or colour change in the hand during injection: stop and report at once.
- After: watch for prolonged sedation if repeated doses were given.
Test yourself
Think of the answer, then tap the question to see it.
Which disease is an absolute contraindication to thiopental and other barbiturates?
Acute intermittent porphyria (and variegate porphyria), because barbiturates can trigger fatal attacks.
Why should rocuronium not be given through the same line right after thiopental?
Thiopental is very alkaline and rocuronium acidic: they precipitate in the line.
What serious local complication follows intra-arterial injection of thiopental?
An intense inflammatory reaction with necrosis that can threaten the limb.
Related drugs
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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.
Sources: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 24 (McGraw Hill, 2023); eEML - Electronic Essential Medicines List (World Health Organization, 2025); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).
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Representative model, for educational purposes only.