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General

As with any potent general anesthetic, isoflurane should only be administered in an adequately equipped anesthetizing environment by those who are familiar with the pharmacology of the drug and qualified by training and experience to manage the anesthetized patient.

Regardless of the anesthetics employed, maintenance of normal hemodynamics is important to the avoidance of myocardial ischemia in patients with coronary artery disease 4,5,6,7.

Isoflurane, like some other inhalational anesthetics, can react with desiccated carbon dioxide (CO 2 ) absorbents to produce carbon monoxide, which may result in elevated levels of carboxyhemoglobin in some patients. Case reports suggest that barium hydroxide lime and soda lime become desiccated when fresh gases are passed through the CO 2 absorber canister at high flow rates over many hours or days. When a clinician suspects that CO 2 absorbent may be desiccated, it should be replaced before the administration of isoflurane .

As with other halogenated anesthetic agents, Isoflurane may cause sensitivity hepatitis in patients who have been sensitized by previous exposure to halogenated anesthetics ( see CONTRAINICATIONS).

Information for Patients

Isoflurane, as well as other general anesthetics, may cause a slight decrease in intellectual function for 2 or 3 days following anesthesia. As with other anesthetics, small changes in moods and symptoms may persist for up to 6 days after administration.

Laboratory Tests

Transient increases in BSP retention, blood glucose and serum creatinine with decrease in BUN, serum cholesterol and alkaline phosphatase have been observed.

Drug Interactions

Isoflurane potentiates the muscle relaxant effect of all muscle relaxants, most notably nondepolarizing muscle relaxants, and MAC (minimum alveolar concentration) is reduced by concomitant administration of N 2 O. ( See CLINICAL PHARMACOLOGY).

Carcinogenesis & Mutagenesis & Impairment Of Fertility

Swiss ICR mice were given isoflurane to determine whether such exposure might induce neoplasia. Isoflurane was given at 1/2, 1/8 and 1/32 MAC for four in-utero exposures and for 24 exposures to the pups during the first nine weeks of life. The mice were killed at 15 months of age. The incidence of tumors in these mice was the same as in untreated control mice, which were given the same background gases, but not the anesthetic.

Pregnancy

Pregnancy Category C

Isoflurane has been shown to have a possible anesthetic-related fetotoxic effect in mice when given in doses 6 times the human dose. There are no adequate and well-controlled studies in pregnant women. Isoflurane should be used during pregnancy only if the potential benefit justifies the potential risk to the fetus.

Nursing Mothers

It is not known whether this drug is excreted in human milk. Because many drugs are excreted in human milk, caution should be exercised when isoflurane is administered to a nursing woman.

ADVERSE REACTIONS


Adverse reactions encountered in the administration of isoflurane are in general dose dependent extensions of pharmacophysiologic effects and include respiratory depression, hypotension and arrhythmias.
Shivering, nausea, vomiting and ileus have been observed in the postoperative period.
As with all other general anesthetics, transient elevations in white blood count have been observed even in the absence of surgical stress. See WARNINGSfor information regarding malignant hyperthermia and elevated carboxyhemoglobin levels.
During marketing, there have been rare reports of mild, moderate and severe (some fatal)
postoperative hepatic dysfunction and hepatitis.
Isoflurane has also been associated with perioperative hyperkalemia (see WARNINGS). There have been rare post-marketing reports of hepatic failure and hepatic necrosis associated with the use of potent volatile anesthetics, including Isoflurane. Due to the spontaneous nature of these reports, the actual incidence and relationship of Isoflurane to these events cannot be established with certainty.

OVERDOSAGE

In the event of overdosage, or what may appear to be overdosage, the following action should be taken:

Stop drug administration, establish a clear airway and initiate assisted or controlled ventilation with pure oxygen.

DOSAGE & ADMINISTRATION

Premedication


Premedication should be selected according to the need of the individual patient, taking into account that secretions are weakly stimulated by isoflurane, and the heart rate tends to be increased. The use of anticholinergic drugs is a matter of choice.

Inspired Concentration

The concentration of isoflurane being delivered from a vaporizer during anesthesia should be known. This may be accomplished by using:

a) vaporizers calibrated specifically for isoflurane;

b) vaporizers from which delivered flows can be calculated, such as vaporizers delivering a saturated vapor which is then diluted. The delivered concentration from such a vaporizer may be calculated using the formula:


Forumula1
where: P A = Pressure of atmosphere A

P V = Vapor pressure of isoflurane

F V = Flow of gas through vaporizer (mL/min)

F T = Total gas flow (mL/min)

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

Induction

Induction with isoflurane in oxygen or in combination with oxygen-nitrous oxide mixtures may produce coughing, breath holding, or laryngospasm. These difficulties may be avoided by the use of a hypnotic dose of an ultra-short-acting barbiturate. Inspired concentrations of 1.5 to 3.0% isoflurane usually

produce surgical anesthesia in 7 to 10 minutes.

Maintenance

Surgical levels of anesthesia may be sustained with a 1.0 to 2.5% concentration when nitrous oxide is used concomitantly. An additional 0.5 to 1.0% may be required when isoflurane is given using oxygen alone. If added relaxation is required, supplemental doses of muscle relaxants may be used.

The level of blood pressure during maintenance is an inverse function of isoflurane concentration in the absence of other complicating problems. Excessive decreases may be due to depth of anesthesia and in such instances may be corrected by lightening anesthesia.

HOW SUPPLIED


Isoflurane, USP is packaged in 100 mL and 250 mL amber-colored bottles.

100 ML — NDC 66794-011-10

250 ML — NDC 66794-011-25

SAFETY AND HANDLING

Occupational Caution
There is no specific work exposure limit established for Isoflurane. However, the National Institute for Occupational Safety and Health Administration (NIOSH) recommends that no worker should be exposed at ceiling concentrations greater than 2ppm of any halogenated anesthetic agent over a sampling period not to exceed one hour.

The predicted effects of acute overexposure by inhalation of Isoflurane include headache, dizziness or (in extreme cases) unconsciousness. There are no documented adverse effects of chronic exposure to halogenated anesthetic vapors (Waste Anesthetic Gases or WAGs) in the workplace. Although results of some
epidemiological studies suggest a link between exposure to halogenated anesthetics and increased health problems (particularly spontaneous abortion), the relationship is not conclusive. Since exposure to WAGs is one possible factor in the findings for these
studies, operating room personnel, and pregnant women in particular, should minimize exposure. Precautions include adequate general ventilation in the operating room, the use of a well-designed and well-maintained scavenging system, work practices to
minimize leaks and spills while the anesthetic agent is in use, and routine equipment maintenance to minimize leaks.

STORAGE

Store at 20 o to 25 o C (68 o to 77 o F); excursions permitted to 15 o -30 o C (59 o -86 o F) [see USP Controlled Room Temperature].

Preserve in tight containers.Isoflurane, contains no additivesand has been demonstrated to be stable at room temperature for periods in excess of five years.

REFERENCES

1. J.C. Sill, et al , Anesthesiology 66:273-279, 1987

2. R.F. Hickey, et al , Anesthesiology 68:21-30, 1988

3. C.W. Buffington, et a l , Anesthesiology 66:280-292, 1987

4. S. Reiz, et al , 59:91-97, 1983

5. S. Slogoff and A.S. Keats, Anesthesiology 70:179-188, 1989

6. K.J. Tuman, et al , Anesthesiology 70:189-198, 1989

7. D.T. Mangano, Editorial Views, Anesthesiology 70:175-178, 1989

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