Skip to Content

IsoFlo (Isoflurane USP) (Canada)

This page contains information on IsoFlo (Isoflurane USP) for veterinary use.
The information provided typically includes the following:
  • IsoFlo (Isoflurane USP) Indications
  • Warnings and cautions for IsoFlo (Isoflurane USP)
  • Direction and dosage information for IsoFlo (Isoflurane USP)

IsoFlo (Isoflurane USP)

This treatment applies to the following species:
Company: Zoetis



Inhalation Anesthetic For Use in Horses and Dogs



IsoFlo (isoflurane, USP) 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 as the active ingredient.

Some physical constants are:

Molecular weight


Boiling point at 760 mm Hg


Refractive index n20D


Specific gravity 25°C


Vapor pressure in mm Hg**









**Equation for vapor pressure calculation:

log10Pvap = A + B / T where:

A = 8.056

B = -1664.58

T = °C+273.16

Partition coefficients at 37°C:







Partition coefficients at 25°C - (rubber and plastic):

Conductive rubber/gas


Butyl rubber/gas


Polyvinyl chloride/gas








Butyl acetate/gas


Purity by gas chromatography


Lower limit of flammability in oxygen or nitrous oxide at 9 joules/sec. and 23°C.


Lower limit of flammability in oxygen or nitrous oxide at 900 joules/sec. and 23°C

Greater than useful concentration in anesthesia

Minimum Alveolar Concentration
(MAC) in horses1


Minimum Alveolar Concentration
(MAC) in dogs6


Clinical Pharmacology

IsoFlo (isoflurane, USP) is an inhalation anesthetic used for induction and maintenance of general anesthesia in horses and dogs. Induction and recovery from anesthesia with isoflurane are rapid.2,5 The level of anesthesia may be changed rapidly with isoflurane. Isoflurane is a profound respiratory depressant. RESPIRATION MUST BE MONITORED CLOSELY IN THE HORSE AND DOG, AND SUPPORTED WHEN NECESSARY.

As anesthetic dose is increased, both tidal volume and respiratory rate decrease.3,6 This depression is partially reversed by surgical stimulation, even at deeper levels of anesthesia.

Blood pressure decreases with induction of anesthesia but returns toward normal with surgical stimulation. Progressive increases in depth of anesthesia produce corresponding decreases in blood pressure; however, heart rhythm is stable and cardiac output is maintained with controlled ventilation and normal PaCO2 despite increasing depth of anesthesia. The hypercapnia which attends spontaneous ventilation during isoflurane anesthesia increases heart rate and raises cardiac output above levels observed with controlled ventilation.3 Isoflurane does not sensitize the myocardium to exogenously administered epinephrine in the dog.

Muscle relaxation may be adequate for intra-abdominal operations at normal levels of anesthesia. However, if muscle relaxants are used to achieve greater relaxation, it should be noted that: ALL COMMONLY USED MUSCLE RELAXANTS ARE MARKEDLY POTENTIATED WITH ISOFLURANE, THE EFFECT BEING MOST PROFOUND WITH THE NONDEPOLARIZING TYPE. Neostigmine reverses the effect of nondepolarizing muscle relaxants in the presence of isoflurane but does not reverse the direct neuromuscular depression of isoflurane.

IsoFlo (Isoflurane USP) Indications

IsoFlo (isoflurane, USP) is used for induction and maintenance of general anesthesia in horses and dogs.


IsoFlo (isoflurane, USP) is contraindicated in horses and dogs with known sensitivity to isoflurane or to other halogenated agents.

IsoFlo (Isoflurane USP) Caution

Increasing depth of anesthesia with IsoFlo (isoflurane, USP) may increase hypotension and respiratory depression. The electroencephalographic pattern associated with deep anesthesia is characterized by burst suppression, spiking and isoelectric periods.4

Since levels of anesthesia may be altered easily and rapidly, only vaporizers producing predictable percentage concentrations of isoflurane should be used (see DOSAGE AND ADMINISTRATION).

The action of nondepolarizing relaxants is augmented by isoflurane. Less than the usual amounts of these drugs should be used. If the usual amounts of nondepolarizing relaxants are given, the time for recovery from myoneural blockade will be longer in the presence of isoflurane than in the presence of other commonly used anesthetics.

Usage in Pregnancy - Reproduction studies have been performed in mice and rats with no evidence of fetal malformation attributable to IsoFlo (isoflurane, USP). Adequate data concerning the safe use of isoflurane in pregnant and breeding horses and dogs have not been obtained.

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.

Adverse Reactions

Hypotension, respiratory depression and arrhythmias have been reported. For Technical Support and Customer Service please call 1-888-299-7416.


1. This drug must not be administered to horses that are to be slaughtered for use in food.

2. Operating rooms should be provided with adequate ventilation to prevent the accumulation of anesthetic vapors.

IsoFlo (Isoflurane USP) Dosage And Administration

WARNING: Operating rooms should be provided with adequate ventilation to prevent the 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 IsoFlo (isoflurane, USP) 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. Verni-trol® vaporizer) also may be used. The delivered concentration from such a vaporizer may be calculated using the formula:

% isoflurane =




Where: PA = Pressure of atmosphere

PV = Vapor pressure of isoflurane

FV = Flow of gas through vaporizer (mL/ minute)

FT = Total gas flow used (mL/ minute)

Isoflurane contains no stabilizer. Nothing in the drug product alters calibration or operation of these vaporizers.


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. Surgical levels of anesthesia in the horse 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


Store at room temperature, 15°C-30°C (59°F-86°F).

How Supplied

IsoFlo (isoflurane, USP) is available in 250 mL amber-colored bottles.


1. Steffey, E.P., Howland, D. Jr., Giri, S. and Eger, E.I.II.: Enflurane, Halothane and Isoflurane Potency in Horses. Am. J. Vet. Res. 38(7): 1037-1039, 1977.

2. Auer, J.A., Garner, H.E., Amend, J.F., Hutcheson, D.P. and Salem, C.A.: Recovery from Anesthesia in Ponies: A Comparative Study of the Effects of Isoflurane, Enflurane, Methoxyflurane and Halothane. Equine Vet. J. 10(1): 18-23, 1978.

3. Steffey, E.P. and Howland, D. Jr.: Comparison of Circulatory and Respiratory Effects of Isoflurane and Halothane Anesthesia in Horses. Am. J. Vet. Res. 41(5): 821-825, 1980.

4. Auer, J.A., Amend, J.F., Garner, H.E., Hutcheson, D.P. and Salem, C.A.: Electroencephalographic Responses During Volatile Anesthesia in Domestic Ponies: A Comparative Study of Isoflurane, Enflurane, Methoxyflurane, and Halothane. Equine Practice 3: 130-134, 1979.

5. Klide, A.M.: Cardiopulmonary Effects of Enflurane and Isoflurane in the Dog. Am. J. Vet. Res., Vol. 37, No. 2: 127-131, 1976.

6. Steffey, E.P., Howland, D. Jr.: Isoflurane Potency in the Dog and Cat. Am. J. Vet. Res., Vol. 38, No. 11: 1833-1836, 1977.

Manufactured for: Zoetis Canada Inc., Kirkland QC H9H 4M7

Phone: 1-800-461-0917

Issued Oct., 2002



CPN: 1198499.0

Order Desk:   800-663-8888
Technical Services Canada:   800-461-0917
Technical Services USA:   800-366-5288
Every effort has been made to ensure the accuracy of the IsoFlo (Isoflurane USP) information published above. However, it remains the responsibility of the readers to familiarize themselves with the product information contained on the Canadian product label or package insert.

Copyright © 2021 Animalytix LLC. Updated: 2020-12-31