Isoflurane: veterinary dose and monograph

At a glance

Drug class

Sedative / anaesthetic

Also known as

Isoflo, Forane, Sorane, Aerrane

Species with doses

Dogs, Cats, Cattle, Horses, Goats, Sheep, Pigs, Birds, Rabbits, Reptiles, Hedgehogs, Sugar gliders and Small mammals

Routes

Inhaled

Last reviewed

1 October 2026

Indications

• Maintenance of general anaesthesia (all common species)
• Mask/chamber induction (small/exotic patients, where appropriate)
• Anaesthesia where rapid adjustment of depth and quick recovery are needed

Isoflurane dose by species

Doses are per administration unless stated. mg/kg doses scale with body weight; per-animal, per-quarter and infusion-rate doses are shown as the reference writes them.

Dogs

• Induction / maintenance (MAC ≈ 1.3 %): Papich 5e and Plumb’s p.669: 5% induction, 1.5–2.5% maintenance; 0.5–3% (Hubbell). Required vaporiser setting rises as fresh-gas flow falls; premedication and analgesics reduce requirement. Minimal analgesia.

Cats

• Induction / maintenance (MAC ≈ 1.6 %): Papich 5e and Plumb’s p.669: 5% induction, 1.5–2.5% maintenance. Premedication reduces requirement.

Cattle

• Maintenance: Papich 5e (large animals): MAC 1.5–2%. Intubate (regurgitation risk) and ventilate recumbent ruminants; minimal analgesia — add local blocks/NSAIDs.

Horses

• Maintenance: Papich 5e (large animals): MAC 1.5–2%. Sedate for recovery to limit injury.

Goats

• Maintenance: Papich 5e (large animals): MAC 1.5–2%. Intubate after IV induction and support ventilation.

Sheep

• Maintenance: Papich 5e (large animals): MAC 1.5–2%. Intubate (regurgitation risk) and support ventilation.

Pigs

• Maintenance: Papich 5e (large animals): MAC 1.5–2%. Volatile agents can trigger malignant hyperthermia in susceptible pigs — watch for hypercapnia and hyperthermia; dantrolene is the antidote.

Buffalo

No buffalo-specific doses are on file, so buffalo are dosed as cattle.

• Maintenance: Papich 5e (large animals): MAC 1.5–2%. Intubate (regurgitation risk) and ventilate recumbent ruminants; minimal analgesia — add local blocks/NSAIDs.

Birds

• Induction / maintenance (agent of choice): Plumb’s p.669: induction in 1–2 min at 3–5% (small birds 15–30 s at 4%), maintenance 1.5–2% (Bennett 2002; Ludders 1992); recovery within about 5 min. Monitor ventilation closely.

Rabbits

• Induction / maintenance: Plumb’s 10e p.697 (rabbits, ferrets and rodents, extra-label): premedicate with injectable drugs; IV or IM induction is usually preferred, but face-mask induction can follow adequate sedation — 2–3% isoflurane in oxygen via a tight-fitting mask is usually adequate; maintain on 1–2% depending on concurrent drugs and procedure. Rabbits breath-hold during mask/chamber induction — premedicate and pre-oxygenate. Papich 5e gives no rabbit percentages.

Reptiles

• Induction / maintenance: Plumb’s p.669: 5% in a chamber — induction may take 30–60 min (15–30 min after ketamine 10–20 mg/kg); maintenance 3–5% alone (Gillespie 1994) or 1.5–3% (Funk 2002). Breath-holding slows uptake — intubate and ventilate; keep warm.

Hedgehogs

• Induction / maintenance (anaesthetic of choice): Carpenter’s Exotic Animal Formulary (hedgehog table): chamber induction 3–5%, then 2–3% by mask, ET tube or supraglottic device; chamber induction lets the hedgehog uncurl.

Sugar gliders

• Induction / maintenance (anaesthetic of choice): Carpenter’s Exotic Animal Formulary (sugar glider table): induction 5%, maintenance 1–3%.

Small mammals

• Induction / maintenance (rodents, ferrets): Plumb’s p.669: mice, rats, gerbils, hamsters, guinea pigs and chinchillas — induction 2–3%, maintenance 0.25–2% (Adamcak & Otten 2000); ferrets premedicated with medetomidine + atropine, starting at 1–2% (Johnson 2006). Prevent hypothermia.

Contraindications

Malignant-hyperthermia-susceptible patients (especially pigs — though isoflurane is a weaker trigger than older agents). Severe hypovolaemia/shock without resuscitation (potent vasodilator/hypotension). Always requires airway control, oxygen and monitoring. Hepatic disease is a minor concern given low metabolism. Known hypersensitivity.

Species-specific warnings

Pigs: Malignant hyperthermia–susceptible pigs can be triggered by volatile anaesthetics — have dantrolene and cooling ready; monitor temperature and capnography.

Horses: Provide sedation and a padded, assisted recovery — unmedicated isoflurane recoveries can be violent and cause fractures.

Adverse effects

• Dose-dependent hypotension (vasodilation) and respiratory depression
• Reduced cardiac output; bradycardia
• Hypothermia during prolonged anaesthesia
• Rough recovery in horses without sedation
• Environmental/occupational exposure (waste gas — scavenge)

Drug interactions

• Premedicants/opioids/alpha-2 agonists/benzodiazepines: reduce required isoflurane (MAC-sparing) — lower the vaporiser setting
• Other vasodilators/myocardial depressants: additive hypotension
• Catecholamines: isoflurane sensitises the myocardium to arrhythmias less than older agents but caution remains
• Nitrous oxide: reduces isoflurane requirement (combined technique)

Pregnancy and lactation

Crosses the placenta and depresses the neonate during caesarean — minimise depth/time and resuscitate neonates. No strong evidence of teratogenicity; occupational exposure should be minimised (scavenging).

Monitoring

• Anaesthetic depth (reflexes, eye position, jaw tone)
• Blood pressure (hypotension is the main effect), heart rate/rhythm (ECG)
• Capnography and SpO2; ventilation (assist/IPPV as needed)
• Temperature (active warming)
• Agent monitoring / vaporiser setting; waste-gas scavenging for staff safety

Toxicity and overdose

Overdose (excessive inspired concentration) causes profound hypotension, cardiorespiratory depression, and cardiac arrest. Because uptake/elimination are rapid, depth is quickly corrected by reducing the vaporiser and ventilating with oxygen — its controllability is a major safety feature.

Management: Turn the vaporiser OFF, ventilate with 100 % oxygen to wash out the agent, and support circulation (IV fluids, vasopressors/inotropes as needed) and ventilation. Treat bradycardia/arrhythmia per ALS. Effects resolve rapidly once delivery stops. Address hyperthermia aggressively if malignant hyperthermia is suspected (dantrolene, cooling).

Clinical pearls

• Dose by % / MAC and titrate to the patient — there is no mg/kg for inhalants
• Isoflurane gives little analgesia: use opioids/local blocks/alpha-2 so you can run a lower (safer) vaporiser setting
• Its rapid uptake and elimination make depth highly controllable — the safety lever is the vaporiser dial plus oxygen
• Hypotension from vasodilation is the dominant adverse effect — monitor blood pressure and support it
• Horses need sedation for recovery to prevent injury during the excitable emergence

Mechanism of action

Like other volatile anaesthetics it produces reversible unconsciousness by potentiating inhibitory ion channels (GABA-A and glycine receptors) and inhibiting excitatory transmission (NMDA, certain potassium-channel effects) throughout the CNS, depressing the reticular activating system. Anaesthetic potency is described by MAC; minimal hepatic metabolism gives fast, predictable on/off control.

Formulations and products

• Volatile liquid for vaporiser (250 mL bottle)
• Isoflo (Zoetis) — 99.9 % volatile liquid (250 mL), Inhalant (vaporiser)
• Sorane / Iso-Vet (Various (India)) — Isoflurane USP (250 mL), Inhalant (vaporiser)
• Forane — Isoflurane volatile liquid, Inhalant (human-label)

Storage

Volatile liquid: 15–30 °C, keep tightly capped and upright, away from heat/flame. Use only in an appropriate agent-specific vaporiser; scavenge waste gas.

Before you use this dose

Reference doses for veterinary professionals. Confirm the dose against the product label, the patient’s condition, current guidance and local regulations before use; the attending veterinarian remains responsible for every clinical decision.

Other sedatives and anaesthetics

• Dexmedetomidine
• Diazepam
• Etomidate
• Guaifenesin (GGE)
• Ketamine HCl
• Medetomidine
• Midazolam
• Pentobarbital (Pentobarbitone)

Frequently asked questions