Federal law restricts this drug to use by or on the order of a licensed veterinarian.

Isoflurane, USP is a nonflammable, nonexplosive general inhalation anesthetic agent. Its chemical name is l-chloro-2,2,2-trifluoroethyl difluoromethyl ether, and its structural formula is:

Each mL contains 99.9% isoflurane.

Some physical constants are:

**Equation for vapor pressure calculation:

log10Pvap= A + B/T                

where:             A = 8.056

B = -1664.58

T = °C + 273.16 (Kelvin)

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, ethereal odor. Samples stored in indirect sunlight in clear, colorless glass for five years, as well as samples directly exposed for 30 hours to a 2 amp, 115 volt, 60 cycle long wave U.V. light were unchanged in composition as determined by gas chromatography. Isoflurane in one normal sodium methoxide-methanol solution, a strong base, for over six months consumed 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.

Isoflurane, USP is an inhalation anesthetic. 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.

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

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

Increasing depth of anesthesia with 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.

Not for use in horses intended for food.

Keep out of reach of children.

Isoflurane, USP like 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,USP.

Hypotension, respiratory depression, and arrhythmias have been reported.

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.

Isoflurane, USP is packaged in 100 mL (NDC 50989-150-12) and 250 mL (NDC 50989-150-15) amber-colored bottles.

1. Steffey EP, Howland D Jr, Giri S, Eger E1 II.
Enflurane, Halothane and Isoflurane Potence in Horses. AM J Vet Res. 38(7): 1037-1039, 1977.
2.Auer JA, Garner HE, Amend JF, Hutcheson DP, Salem CA.Recovery from Anesthesia in Ponies: A Comparative Study of the Effects of Isoflurane, Enflurane, Methoxyflurane and Halothane.Equine Vet J.10 (1): 18-231978.
3.Steffey Ep, 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 JA, Amend JF, Garner HE, Hutcheson DP, Salem CA. Electroencephalographic Responses During Volatile Anesthesia in DOmestic Ponies: A Comparative Study of Isoflurane, Enflurane, Methoxyflurane, andHalothane.Equine Practice 3: 130-134, 1979.
5. Klide A.M. Cardiopulmonary Effects of Enflurane and Isoflurane in the Dog. AmJ.Vet.Res: Vol.37, No2: 127-131, 1976.
6. Steffey EP, Howland D: Isoflurane Potency in the Dog and Cat. Am J Vet Res., Vol.38, No 11: 1833-1836, 1977

Text revised September 2011