Isoflurane
1-chloro-2,2,2-trifluoroethyl difluoromethyl ether
Also known as: Isoflo · Iso-Thesia · Forane · Isosol · Terrell · Isoba · Isocare · Isofane · Isoflurane Vet · Vetflurane · compound 469 · isofluranum · AErrane · Forene · Forenium · Forthane · Isoforine · Isothane · Lisorane · Sofloran · Tensocold · Zuflax
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
Green iguanas/15–35 min loss of righting reflex; mean MAC, 1.62%; pH 7.49
TABLE 127.5. Agent: Isoflurane. Dosage: 5% via chamber in 5 L/min O2129. Species/Comments: Green iguanas/15–35 min loss of righting reflex; mean MAC, 1.62%; pH 7.49.
Evidence only — not for automatic calculation
Bearded dragons/trend toward shorter induction and recovery with 21% O2 group compared with use of 100% O2
TABLE 127.5. Agent: Isoflurane. Dosage: 3% in 100% O2 and 21% O2248. Species/Comments: Bearded dragons/trend toward shorter induction and recovery with 21% O2 group compared with use of 100% O2.
Evidence only — not for automatic calculation
Most species/inhalation anesthetic of choice in reptiles; induction, 6–20 min; recovery, 30–60 min; not as smooth in reptiles compared with other animals; intubation and intermittent positive pressure ventilation advisable; may preanesthetize with low dose propofol, ketamine, etc.
TABLE 127.5. Agent: Isoflurane. Dosage: 3%–5% induction,147 1%–3% maintenance37. Species/Comments: Most species/inhalation anesthetic of choice in reptiles; induction, 6–20 min; recovery, 30–60 min; not as smooth in reptiles compared with other animals; intubation and intermittent positive pressure ventilation advisable; may preanesthetize with low dose propofol, ketamine, etc..
Doses are a clinical reference for licensed veterinary professionals. Always confirm against the current label and the individual patient.
Overview
Isoflurane is a widely used inhalant general anesthetic in veterinary medicine.
Key clinical features include:
- Cardiovascular safety: It produces less myocardial depression and catecholamine sensitization compared to older agents like halothane.
- Organ safety: It undergoes minimal hepatic metabolism (only ~0.17%), making it a safe choice for patients with pre-existing hepatic or renal disease.
- Clinical Pearl: While newer agents like sevoflurane offer faster changes in anesthetic depth and smoother mask inductions, isoflurane remains a highly reliable and cost-effective staple in veterinary anesthesia.
Mechanism of action
The exact mechanism of inhalant anesthetics remains partially understood, but they are believed to act on the lipid matrix of neuronal membranes and interact with various ligand-gated ion channels (e.g., GABA_A receptors) in the brain and spinal cord.
Key physiological effects:
- CNS: Reversible depression, altered temperature regulation, increased cerebral blood flow.
- Cardiovascular: Dose-dependent hypotension (primarily via vasodilation rather than direct myocardial depression).
- Respiratory: Dose-dependent respiratory depression.
MAC (Minimum Alveolar Concentration) values: Dog = 1.5%; Cat = 1.2%; Horse = 1.31%.
Safety & warnings
Contraindications
- History or predilection towards malignant hyperthermia
- Known susceptibility to malignant hyperthermia
Adverse effects
- Dose-related hypotension
- Nausea and vomiting
- Ileus
- Minimal cardiodepression
- Rare arrhythmias
- Dose-dependent hypotension (due to vasodilation, particularly in skeletal muscle)
- Dose-dependent respiratory depression
- Arrhythmias (less arrhythmogenic than halothane, but possible under certain conditions)
- Hypothermia
Precautions
Use with caution in patients with increased CSF pressure, head injury, or myasthenia gravis. Because of respiratory depressant effects, intermittent positive pressure ventilation (IPPV) may be required, particularly in horses, which increases overdose risks. Isoflurane is irritating to the respiratory system and is not recommended for mask induction. May be fetotoxic; use cautiously during pregnancy.
Drug interactions
Additive neuromuscular blockade may occur
Concomitant use may increase risks for profound hypotension
Additive neuromuscular blockade may occur
Additive neuromuscular blockade may occur
May induce increased incidences of cardiac effects (bradycardia, arrhythmias) and malignant hyperthermia in susceptible patients
May result in arrhythmias, though isoflurane sensitizes the myocardium less than halothane. Use with caution and intensive monitoring.
Reduces the concentration of isoflurane required to achieve surgical anaesthesia (MAC reduction).
Reduces the concentration of isoflurane required to achieve surgical anaesthesia (MAC reduction).
Reduces the concentration of isoflurane required to achieve surgical anaesthesia.
Monitoring
- Respiratory and ventilatory status
- Cardiac rate and rhythm
- Blood pressure (particularly in 'at risk' patients)
- Level of anesthesia
- Respiratory rate, rhythm, and depth (capnography/ETCO2 recommended)
- Heart rate and rhythm (ECG)
- Blood pressure (Doppler or oscillometric)
- Oxygen saturation (Pulse oximetry/SpO2)
- Body temperature
- Anaesthetic depth (eye position, palpebral reflex, jaw tone)
Pharmacokinetics
Half-life
Absorption
Rapidly absorbed from the alveoli.
Distribution
Rapidly distributed into the CNS and crosses the placenta.
Metabolism
Only about 0.17% is metabolized in the liver; very small amounts of inorganic fluoride are formed.
Elimination
The vast majority of the drug is eliminated unchanged via the lungs.
Overdose
Overdose risks are increased with intermittent positive pressure ventilation. Profound hypotension may occur, which usually responds to IV fluids but may require the use of vasopressors.
Available products
Formulations
- Liquid for inhalation
- Inhalational liquid: 250 ml bottle
Veterinary
- Isoflurane Inhalation Anesthetic: 99.9%/mL in 100 mL and 250 mL bottles (Isoflo, Isosol, Iso-Thesia, generic)
- Isoba 100% w/w inhalation vapour, liquid
- Isocare 100% w/w inhalation vapour, liquid
- Isofane 100% w/w inhalation vapour, liquid
- IsoFlo 100% w/w inhalation vapour, liquid
- Isoflurane Vet 100% w/w inhalation vapour, liquid
- Vetflurane 100% w/w inhalation vapour, liquid
Human-labeled
- Isoflurane Liquid for inhalation in 100 mL & 250 mL (Forane, Terrell, generic)
- Isoflurane 100% inhalation vapour, liquid
Regulatory status
Withdrawal times: pigs meat 2 days · horses meat 2 days
POM-V classification.
Withdrawal times: pigs meat 2 days · horses meat 2 days
POM-V classification.
No regulatory data for: 🇺🇸 US · 🇭🇰 HK · 🇹🇼 TW · 🇯🇵 JP · 🇰🇷 KR · 🇦🇺 AU
Storage & stability
Store at room temperature in a tight, light-resistant container. It is relatively unaffected by exposure to light. Isoflurane does not attack aluminum, brass, tin, iron, or copper.
Client information
Isoflurane is an anesthetic gas administered by veterinary professionals in a clinical setting.
- Post-Anesthesia Care: Your pet may be groggy, uncoordinated, or have a mild cough (from the breathing tube) for 12-24 hours after the procedure.
- Feeding: Offer small amounts of water and food initially to prevent nausea, unless directed otherwise by your veterinarian.
- Monitoring: Keep your pet in a quiet, safe, and warm environment while they fully recover.
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.