Isoflurane

Indications

Isoflurane is used for induction and maintenance of general anesthesia in horses and dogs.

Dosage and Administration

Caution: Operating rooms and animal recovery areas should be provided with adequate ventilation to prevent accumulation of anesthetic vapors. Premedication: A premedication regimen, which may be employed depending upon the patient status, to avert excitement during induction, might include an anticholinergic, a tranquilizer, a muscle relaxant, and a short-acting barbiturate. Inspired Concentration: The delivered concentration of Isoflurane should be known. Isoflurane may be vaporized using a flow-through vaporizer specifically calibrated for isoflurane. Vaporizers delivering a saturated vapor which then is diluted (e.g., Vernitrol® vaporizer) also may be used. The delivered concentration from such a vaporizer may be calculated using the formula: % isoflurane = 100P₍ᵥ₎F₍ᵥ₎ ────────────── F₍ₜ₎(P₍ₐ₎ - P₍ᵥ₎) Where: Pₐ = Pressure of atmosphere Pᵥ = Vapor pressure of isoflurane Fᵥ = Flow of gas through vaporizer (mL/min) Fₜ = Total gas flow used (mL/min) Isoflurane contains no stabilizer. Nothing in the drug product alters calibration or operation of these vaporizers. Induction Horses: Inspired concentrations of 3.0 to 5.0% isoflurane alone with oxygen following a barbiturate anesthetic induction are usually employed to induce surgical anesthesia in the horse. Dogs: Inspired concentrations of 2.0 to 2.5% isoflurane alone with oxygen following a barbiturate anesthetic induction are usually employed to induce surgical anesthesia in the dog. These concentrations can be expected to produce surgical anesthesia in 5 to 10 minutes. Maintenance: The concentration of vapor necessary to maintain anesthesia is much less than that required to induce it. Horses: Surgical levels of anesthesia in the horse may be sustained with a 1.5 to 1.8% concentration of isoflurane in oxygen. Dogs: Surgical levels of anesthesia in the dog may be sustained with a 1.5 to 1.8% concentration of isoflurane in oxygen. The level of blood pressure during maintenance is an inverse function of isoflurane concentration in the absence of other complicating problems. Excessive decreases, unless related to hypovolemia, may be due to depth of anesthesia and in such instances may be corrected by lightening the level of anesthesia. Recovery from isoflurane anesthesia is typically uneventful.²

Contraindications

Isoflurane is contraindicated in horses and dogs with known sensitivity to isoflurane or to other halogenated agents.

Warnings

Not for use in horses intended for human consumption. Not for use in Humans. Keep Out of Reach of Children.

Precautions

Isoflurane, like some other inhalational anesthetics, can react with desiccated carbon dioxide (CO₂) absorbents to produce carbon monoxide which may result in elevated carboxyhemoglobin levels in some patients. Case reports suggest that barium hydroxide lime and soda lime become desiccated when fresh gases are passed through the CO₂ absorber canister at high flow rates over many hours or days. When a clinician suspects that CO₂ absorbent may be desiccated, it should be replaced before the administration of isoflurane. Usage in Pregnancy: Reproduction studies have been performed in mice and rats with no evidence of fetal malformation attributable to isoflurane. Adequate data concerning the safe use of isoflurane in pregnant and breeding horses and dogs have not been obtained.

Adverse Reactions

Hypotension, respiratory depression and arrhythmias have been reported. OVERDOSAGE In the event of overdosage, or what may appear to be overdosage, the following action should be taken: Stop drug administration, establish that the airway is clear and initiate assisted or controlled ventilation with pure oxygen as circumstances dictate.

Description

Isoflurane is a nonflammable, nonexplosive general inhalation anesthetic agent. Its chemical name is 1-chloro-2,2,2-trifluoroethyl difluoromethyl ether, and its structural formula is: Each mL contains 99.9% isoflurane. Some physical constants are: Some physical constants are: Molecular weight ............................................... 184.5 Boiling point at 760 mm Hg ................................ 48.5°C (uncorr.) Refractive index n20D ....................................... 1.2990-1.3005 Specific gravity 25°/25°C .................................. 1.496 Vapor pressure in mm Hg** ...................................... 20°C 238 25°C 295 30°C 367 35°C 450 **Equation for vapor pressure calculation: log10 Pv = A + B/(T + C) A = 8.056 B = -1664.58 T = °C + 273.16 (Kelvin) Partition coefficients at 37°C: Water/gas .................................................... 0.61 Blood/gas .................................................... 1.43 Oil/gas ........................................................ 90.8 Partition coefficients at 25°C – rubber and plastic: Conductive rubber/gas ....................................... 62.0 Butyl rubber/gas ............................................... 75.0 Polyvinyl chloride/gas ...................................... 110.0 Polyethylene/gas ............................................. ~2.0 Polyurethane/gas ............................................. ~1.4 Polyolefin/gas .................................................. ~1.1 Butyl acetate/gas ............................................. ~2.5 Purity by gas chromatography ........................ >99.9% Lower limit of flammability in oxygen or nitrous oxide at 9 joules/sec and 23°C .................. None Lower limit of flammability in oxygen or nitrous oxide at 900 joules/sec and 23°C ........ Greater than useful concentrations in anesthesia MAC (Minimum Alveolar Concentration) is 1.31% in horses¹ and 1.28% in dogs.⁶. Isoflurane is a clear, colorless, stable liquid containing no additives or chemical stabilizers. Isoflurane has a mildly pungent, musty, etheral odor. Samples stored in indirect sunlight in clear, colorless glass for five years, as well as samples directly exposed for 30 hours to a 24,000 ft. candle tungsten light, showed no change in composition as determined by gas chromatography. Isoflurane in one normal sodium methoxide-methanol solution, a strong base, for two months contained essentially no alkali, indicative of strong base stability. Isoflurane does not decompose in the presence of soda lime (at normal operating temperatures), and does not attack aluminum, tin, brass, iron, or copper. Structural Formula

Other labels for this ingredient

These labels are also stored for the same active ingredient. They are not identical to the one reprinted above, and each is listed by product and set id rather than merged with it.

• WARNING: Not for use in horses intended for food Isoflurane, USP Inhalation Anesthetic For Veterinary Use in Horses and Dogs, Piramal Critical Care Inc. Set id b0c8964f-24a8-4bab-ae8d-1536737e43ec.
• Isospire™ (isoflurane) Inhalation Anesthetic For Use in Horses and Dogs, Dechra Veterinary Products LLC. Set id 816dc04f-6106-47c8-a7d5-34e2d542b212.
• WARNING: Not for use in horses intended for food. IsoSol™ Isoflurane USP Inhalation Anesthetic For Veterinary Use in Horse and Dogs, Vedco, Inc.. Set id b69c2259-d7d8-482d-8443-6279d217da0a.

FDA adverse event reports

The FDA Center for Veterinary Medicine publishes the adverse event reports it receives through openFDA. The counts below are the reports naming isoflurane as an active ingredient for each species this label names, as returned on 2026-09-16, coded by the VeDDRA reaction term the reporter chose. Reactions are counted per report, so one report can appear under several terms.

These are counts, not rates. Reporting is voluntary, the number of animals treated is not known, and a widely used product accumulates reports for that reason alone. A report records that an event followed a dose; it does not establish that the product caused it. The counts say nothing about how one product compares with another.