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[Pharmacology](https://durgical.com/en/pharmacology/) · [Intravenous anaesthetics](https://durgical.com/en/pharmacology/classes/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

- Class: [Intravenous anaesthetics](https://durgical.com/en/pharmacology/classes/intravenous-anaesthetics/)
- Receptor: GABA-A receptor
- ATC code: N01AF03

## ⚠ High-alert medication

An error with this medicine can cause serious harm: double checks and protocols are used.

Also called: Thiopental sodium, Thiopentone

◎**GABA-A receptor**Thiopental

ⓘ There is no structure with thiopental. The figure shows phenobarbital, another barbiturate, bound to the human α1β2γ2 GABA-A receptor with GABA.

**Target in 3D:** GABA-A receptor. PDB structure 6X3W (RCSB PDB, public domain). [View the structure at RCSB PDB](https://www.rcsb.org/structure/6X3W) · Drag to rotate · pinch to zoom

## 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

### Serious (rare, important)

- Attacks of acute porphyria, sometimes fatal
- Severe necrosis if injected into an artery
- Severe hypotension in hypovolaemia or heart disease
- Unconsciousness for days after large doses or infusions

## 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.

## Memory aid

THIOpental: «Takes seconds, Hurts the artery, Inflames porphyria, Out fast by redistribution».

## 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.

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## Related drugs

- [Propofol](https://durgical.com/en/pharmacology/propofol/)
- [Etomidate](https://durgical.com/en/pharmacology/etomidate/)

[← Back to the class: Intravenous anaesthetics](https://durgical.com/en/pharmacology/classes/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: Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 24 (McGraw Hill, 2023); [eEML - Electronic Essential Medicines List](https://list.essentialmeds.org/) (World Health Organization, 2025); [ATCDDD - ATC/DDD Index](https://atcddd.fhi.no/atc_ddd_index/?code=N01AF03) (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.

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