ISOFLURANE

Chemistry - An inhalant general anesthetic agent, isoflurane occurs as a colorless, nonflammable, stable liquid. It has a characteristic mildly pungent musty, ethereal odor. At 20°C, isoflurane'sspecific gravity is 1.496 and vapor pressure is 238 mm Hg.

Storage, Stability, Compatibility

Isoflurane should be stored at room temperature; it is relatively unaffected by exposure to light, but should be stored in a tight, light-resistant container.
Isoflurane does not attack aluminum, brass, tin, iron or copper.

Pharmacology - ISOFLURANE

While the precise mechanism that inhalent anesthetics exert their general anesthetic effects is not precisely known, they may interfere with functioning of nerve cells in the brain by acting at the lipid matrix of the membrane. Some key pharmacologic effects noted with isoflurane include: CNS depression, depression of body temperature regulating centers, increased cerebral blood flow, respiratory depression, hypotension, vasodilatation, and myocardial depression (less so than with halothane) and muscular relaxation.
Minimal Alveolar Concentration (MAC; %) in oxygen reported for isoflurane in various species:
Dog = 1.5; Cat = 1.2; Horse = 1.31; Human = 1.2. Several factors may alter MAC (acid/base status, temperature, other CNS depressants on board, age, ongoing acute disease, etc.).
Uses, Indications - Isoflurane is an inhalant anesthetic that has some distinct advantages over either halothane or methoxyflurane due to its lessened myocardial depressant and catecholamine sensitizing effects, and the ability to use it safely in patients with either hepatic or renal disease.
Isoflurane's higher cost than either methoxyflurane or halothane is a disadvantage.
Horses may recover more rapidly than with halothane, but be more susceptible to anesthetic associated-myopathy.

Pharmacokinetics - ISOFLURANE

Isoflurane is rapidly absorbed from the alveoli. It is rapidly distributed intothe CNS and crosses the placenta. The vast majority of the drug is eliminated via the lungs; onlyabout 0.17% is metabolized in liver and only very small amounts of inorganic fluoride is formed.

Contraindications, Precautions, Reproductive Safety

Isoflurane is contraindicated in patientswith a history or predilection towards malignant hyperthermia. It should be used with caution(benefits vs. risks) in patients with increased CSF or head injury, or myasthenia gravis.
Some animal studies have indicated that isoflurane may be fetotoxic. Use during pregnancy withcaution.

Adverse Effects, Warnings

Hypotension (secondary to vasodilation, not cardiodepression) mayoccur and is considered to be dose related. Dose-dependent respiratory depression, and GI effects(nausea, vomiting, ileus) have been reported. While cardiodepression generally is minimal at dosescausing surgical planes of anesthesia, it may occur. Arrhythmias have also rarely been reported.

Drug Interactions

While isoflurane sensitizes the myocardium to the effects of sympathomimetics less so than halothane, arrhythmias may still result. Drugs included are: dopamine, epinephrine, norepinephrine, ephedrine, metaraminol, etc. Caution and monitoring is advised.
Non-depolarizing neuromuscular blocking agents, systemic aminoglycosides, systemic lincomycins should be used with caution with halogenated anesthetic agents as additive neuromuscular blockade may occur.
Concomitant administration of succinylcholine with inhalation anesthetics may induce increased incidences of cardiac effects (bradycardia, arrhythmias, sinus arrest and apnea) and in susceptible patients, malignant hyperthermia as well.