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Pharmacology · Inhaled anaesthetics

Isoflurane !

Widely used halogenated inhaled anaesthetic for maintaining general anaesthesia. Pungent, it irritates the airway if used for induction.

Updated 2026-11-01

  • Class: Inhaled anaesthetics
  • Target: Several central nervous system ion channels (GABA-A and glycine receptors, potassium channels)
  • ATC code: N01AB06
  • WHO Model List of Essential Medicines

Mechanism of action

Isoflurane, a volatile halogenated ether, enhances inhibitory GABA-A and glycine receptors and activates two-pore-domain potassium channels, depressing neuronal activity and producing unconsciousness and immobility. It is a vasodilator: it lowers vascular resistance and blood pressure, and it depresses the ventilatory response to hypoxia and hypercapnia.

  1. Vaporised and inhaled down to the alveoli
  2. Enhances inhibitory receptors and potassium channels
  3. Unconsciousness and immobility
  4. Concentration-dependent vasodilation and hypotension

Pharmacokinetics

Absorption
Through the lungs; its mild pungency limits the speed of induction.
Metabolism
A very small fraction is metabolised in the liver.
Elimination
Almost all is exhaled unchanged.

Indications

  • Induction and, above all, maintenance of general anaesthesia

Adverse effects

Common

  • Hypotension
  • Reflex tachycardia
  • Respiratory depression
  • Cough, laryngospasm and apnoea from airway irritation
  • Nausea and vomiting
  • Emergence agitation in children

Contraindications

  • Known or suspected genetic susceptibility to malignant hyperthermia
  • Hypersensitivity to isoflurane or other halogenated agents
  • Confirmed hepatitis from a halogenated agent, or unexplained liver dysfunction (jaundice with fever or eosinophilia) after one

Key interactions

Non-depolarising neuromuscular blockers
Enhances and prolongs the block.
Suxamethonium
Higher risk of malignant hyperthermia.
Nitrous oxide and opioids
Lower the MAC.

What is monitored

  • End-tidal agent concentration
  • Blood pressure, ECG and saturation
  • End-tidal CO2 and temperature

Administration and safety

  • Only with a vaporiser calibrated for isoflurane.
  • Replace a desiccated CO2 absorbent before use: it can produce carbon monoxide.
  • Keep dantrolene available where it is used.

Nursing care

  • Before: ask about personal or family malignant hyperthermia, myopathies and previous reactions to halogenated agents.
  • In recovery: breathing, saturation, blood pressure and nausea.
  • Tell parents the child may wake agitated for a short while.

Pregnancy and breastfeeding

It relaxes uterine muscle; animal studies show effects on the developing brain with long exposures.

Test yourself

Think of the answer, then tap the question to see it.

Why is isoflurane not preferred for mask induction?

Its pungent smell irritates the airway and can cause cough, apnoea and laryngospasm; sevoflurane is better tolerated.

Which toxic gas can form if isoflurane passes through a dry CO2 absorbent?

Carbon monoxide.

What effect does isoflurane have on non-depolarising blockers?

It enhances and prolongs the block, so lower doses are needed.

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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: DailyMed - ISOFLURANE, (VOLATILE FOR INHALATION)- isoflurane liquid (DailyMed (U.S. National Library of Medicine), 2026); 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.