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Forane Side Effects

Generic Name: isoflurane

Note: This document contains side effect information about isoflurane. Some of the dosage forms listed on this page may not apply to the brand name Forane.

For the Consumer

Applies to isoflurane: inhalation solution

What are some side effects that I need to call my doctor about right away?

WARNING/CAUTION: Even though it may be rare, some people may have very bad and sometimes deadly side effects when taking a drug. Tell your doctor or get medical help right away if you have any of the following signs or symptoms that may be related to a very bad side effect:

  • Signs of an allergic reaction, like rash; hives; itching; red, swollen, blistered, or peeling skin with or without fever; wheezing; tightness in the chest or throat; trouble breathing, swallowing, or talking; unusual hoarseness; or swelling of the mouth, face, lips, tongue, or throat.
  • Signs of high potassium levels like a heartbeat that does not feel normal; feeling confused; feeling weak, lightheaded, or dizzy; feeling like passing out; numbness or tingling; or shortness of breath.
  • Very bad dizziness or passing out.
  • Trouble breathing, slow breathing, or shallow breathing.
  • A heartbeat that does not feel normal.
  • Muscle stiffness.
  • Change in color of skin to a bluish color like on the lips, nail beds, fingers, or toes.
  • This drug may cause a very bad and sometimes deadly problem called malignant hyperthermia. Call your doctor right away if you have a fast heartbeat, fast breathing, fever, or spasm or stiffness of the jaw muscles.
  • Very bad and sometimes deadly liver problems have happened with this drug. Call your doctor right away if you have signs of liver problems like dark urine, feeling tired, not hungry, upset stomach or stomach pain, light-colored stools, throwing up, or yellow skin or eyes.

What are some other side effects of this drug?

All drugs may cause side effects. However, many people have no side effects or only have minor side effects. Call your doctor or get medical help if any of these side effects or any other side effects bother you or do not go away:

  • Upset stomach or throwing up.
  • Shivering.

These are not all of the side effects that may occur. If you have questions about side effects, call your doctor. Call your doctor for medical advice about side effects.

You may report side effects to the FDA at 1-800-FDA-1088. You may also report side effects at

For Healthcare Professionals

Applies to isoflurane: inhalation liquid


General side effects including malignant hyperthermia and shivering have been observed in the postoperative period.

In general, side effects encountered in the administration of isoflurane (the active ingredient contained in Forane) are dose dependent extensions of pharmacophysiologic effects and include respiratory depression, hypotension, and arrhythmias.[Ref]


Hepatic side effects have included rare reports of mild, moderate, and severe (sometimes fatal) postoperative hepatic dysfunction and hepatitis. There have also been rare postmarketing reports of hepatic failure and hepatic necrosis associated with the use of potent volatile anesthetic agents, including isoflurane (the active ingredient contained in Forane) [Ref]


Gastrointestinal side effects including nausea, vomiting, and ileus have been observed in the postoperative period.[Ref]


Isoflurane (the active ingredient contained in Forane) can react with desiccated carbon dioxide (CO2) absorbents to produce carbon monoxide, which may result in elevated levels of carboxyhemoglobin in some patients.[Ref]

Respiratory side effects including elevated carboxyhemoglobin levels have been reported.[Ref]


Metabolic side effects including perioperative hyperkalemia have been reported.[Ref]


Hematologic side effects including transient elevations in white blood count have been reported even in the absence of surgical stress.[Ref]


1. "Product Information. Forane (isoflurane)." Baxter Pharmaceutical Products, Inc, New Providence, NJ.

Further information

Always consult your healthcare provider to ensure the information displayed on this page applies to your personal circumstances.

Some side effects may not be reported. You may report them to the FDA.

More about Forane (isoflurane)

Consumer resources

Other brands: Terrell

Professional resources

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