Reviewed on 11/10/2022

What Is Isoflurane and How Does It Work?

Isoflurane is a prescription medication used for anesthesia induction and maintenance.

  • Isoflurane is available under the following different brand names: Forane

What Are Dosages of Isoflurane?

Adult dosage

Inhalation solution

  • 100mL
  • 250mL

Anesthesia Induction & Maintenance

Adult dosage

  • Induction: 1.5-3% can produce surgical anesthesia in 7-10 minutes
  • Maintenance: 1-2.5% with nitrous oxide
  • Additional 0.5-1% may be needed if given with oxygen alone

Dosage Considerations – Should be Given as Follows: 

  • See “Dosages”

What Are Side Effects Associated with Using Isoflurane?

Common side effects of Isoflurane include:

  • upset stomach,
  • vomiting, 
  • shivering,
  • slow or shallow breathing,
  • low blood pressure, or
  • abnormally fast or slow heart rate.

Serious side effects of Isoflurane include:

  • hives,
  • difficulty breathing,
  • swelling of the face, lips, tongue, or throat,
  • red, swollen, blistered, or peeling skin with or without fever,
  • wheezing,
  • tightness in the chest or throat,
  • unusual hoarseness,
  • confusion,
  • weakness,
  • lightheadedness,
  • dizziness,
  • numbness or tingling,
  • shortness of breath,
  • fainting,
  • slow breathing,
  • shallow breathing,
  • abnormal heartbeat,
  • muscle stiffness,
  • the bluish skin color of the lips, nails, fingers, or toes,
  • fast heartbeat,
  • fast breathing,
  • fever,
  • spasm or stiffness of the jaw muscles,
  • dark urine,
  • tiredness,
  • loss of appetite,
  • upset stomach,
  • abdominal pain,
  • clay-colored stools,
  • vomiting, and
  • yellowing of the skin or eyes (jaundice).

Rare side effects of Isoflurane include:

  • none 
This is not a complete list of side effects and other serious side effects or health problems that may occur as a result of the use of this drug. Call your doctor for medical advice about serious side effects or adverse reactions. You may report side effects or health problems to FDA at 1-800-FDA-1088.


About how much does an adult human brain weigh? See Answer

What Other Drugs Interact with Isoflurane?

If your medical doctor is using this medicine to treat your pain, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first

  • Isoflurane has severe interactions with no other drugs.
  • Isoflurane has serious interactions with at least 61 other drugs.
  • Isoflurane has moderate interactions with the following drugs:
  • Isoflurane has minor interactions with no other drugs.

This information does not contain all possible interactions or adverse effects. Visit the RxList Drug Interaction Checker for any drug interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you and share this information with your doctor and pharmacist. Check with your health care professional or doctor for additional medical advice, or if you have health questions, concerns.

What Are Warnings and Precautions for Isoflurane?


  • Hypersensitivity to isoflurane & halogenated agents
  • Genetic susceptibility to malignant hyperthermia
  • Patients in whom general anesthesia contraindicated
  • History of confirmed hepatitis due to a halogenated inhalational anesthetic or a history of unexplained moderate to severe hepatic dysfunction (e.g., jaundice associated with fever and/or eosinophilia) after anesthesia with isoflurane or other halogenated inhalational anesthetics

Effects of drug abuse

  • None

Short-Term Effects

  • See “What Are Side Effects Associated with Using Isoflurane?”

Long-Term Effects

  • See “What Are Side Effects Associated with Using Isoflurane?”


  • Caution in coronary heart disease
  • May decrease renal and hepatic blood flow
  • Postoperative hepatic dysfunction and hepatitis reported
  • Adequate data have not been developed to establish its application in obstetrical anesthesia
  • Should not be used as a sole agent of induction in patients with ventricular dysfunction
  • Therapy 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
  • All patients receiving the drug should be continually monitored (e.g., monitoring of the electrocardiogram, blood pressure, oxygen saturation, and end-tidal CO2)
  • nd respiratory depressant; excessive respiratory depression may be related to the depth of anesthesia and respond to decreasing the inspired concentration of isoflurane
  • The depressant effect is accentuated by concurrent use of opioids and other respiratory depressants; respiration should be closely monitored and assisted or controlled ventilation employed when necessary
  • Except for neonates, isoflurane MAC decreases with increasing age
  • QTc prolongation, with rare instances of torsade de pointes, reported; monitor QT interval when administering the drug to susceptible patients
  • Regardless of the anesthetics employed, maintenance of normal hemodynamics is important to the avoidance of myocardial ischemia in patients with coronary artery disease
  • Isoflurane can cause dose-dependent coronary vasodilation and has been shown to divert blood from collateral-dependent myocardium to normally perfused areas in an animal model (“coronary steal”); monitor for signs of inadequate myocardial perfusion via hemodynamic monitors (eg, ECG, blood pressure) during administration; consider additional cardiac monitoring in patients with known coronary artery disease, as clinically necessary
  • Isoflurane causes a dose-dependent reduction in systemic vascular resistance and blood pressure; particular care must be taken when selecting the dosage for patients who are hypovolemic, hypotensive, or otherwise hemodynamically compromised, e.g., due to concomitant medications
  • Increased blood loss comparable to that seen with halothane observed in patients undergoing abortions
  • Allergic-type hypersensitivity reactions, including anaphylaxis, were reported with therapy; manifestations of such reactions have included hypotension, rash, difficulty breathing, and cardiovascular collapse
  • The drug markedly increases cerebral blood flow at deeper levels of anesthesia to produce a transient increase in intracranial pressure; in patients with or at risk for elevations of intracranial pressure (ICP), administer isoflurane in conjunction with ICP- reducing strategies, as clinically appropriate
  • The color indicator of most CO2 absorbents does not necessarily change as a result of desiccation; therefore, the lack of significant color change should not be taken as an assurance of adequate hydration of the CO2 absorbent material; CO2 absorbents should be replaced routinely regardless of the state of color indicator following current manufacturer’s guidelines for use of anesthesiology equipment
  • Reactions reported following occupational exposure to the drug include dyspnea, bronchospasm, stridor, cough, dizziness, paresthesia, hepatic reactions, flushing rash, contact dermatitis, erythema, periorbital edema, eye irritation, conjunctival hyperemia, and headache

Hepatic reactions

  • Cases of mild, moderate, and severe postoperative hepatic dysfunction or hepatitis with or without jaundice, including fatal hepatic necrosis and hepatic failure, reported
  • Such reactions can represent hypersensitivity hepatitis, a known risk of exposure to halogenated anesthetics, including isoflurane
  • As with other halogenated anesthetic agents, the drug may cause sensitivity hepatitis in patients sensitized by previous exposure to halogenated anesthetics
  • Clinical judgment should be exercised when isoflurane drug is used in patients with underlying hepatic conditions or under treatment with drugs known to cause hepatic dysfunction
  • As with all halogenated anesthetics, repeated anesthetics within a short period may result in increased effects, particularly in patients with underlying hepatic conditions, or additive effects in patients treated with drugs known to cause hepatic dysfunction
  • Evaluate the need for repeated exposure in each patient and adjust the dose of isoflurane based on signs and symptoms of adequate depth of anesthesia if repeated exposure in a short period is clinically indicated

Malignant hyperthermia

  • In susceptible individuals, isoflurane anesthesia may trigger a skeletal muscle hypermetabolic state leading to high oxygen demand and the clinical syndrome known as malignant hyperthermia
  • The syndrome includes nonspecific features such as muscle rigidity, tachycardia, tachypnea, cyanosis, arrhythmias, and unstable blood pressure; it should also be noted that many of these nonspecific signs may appear with light anesthesia, acute hypoxia, etc
  • An increase in overall metabolism may be reflected in an elevated temperature, (which may rise rapidly early or late in the case, but usually is not the first sign of augmented metabolism) and increased usage of the CO2 absorption system (hot canister)
  • PaO2 and pH may decrease, and hyperkalemia and a base deficit may appear; treatment includes discontinuance of triggering agents (e.g., isoflurane), administration of intravenous dantrolene sodium, and application of supportive therapy
  • Such therapy includes vigorous efforts to restore body temperature to normal, respiratory and circulatory support as indicated, and management of electrolyte- fluid-acid-base derangements
  • Consult prescribing information for dantrolene sodium intravenous for additional information on patient management
  • Renal failure may appear later, and urine flow should be sustained if possible; the fatal outcome of malignant hyperthermia has been reported with isoflurane

Pediatric use

  • During the induction of anesthesia, saliva flow and tracheobronchial secretion can increase and can be the cause of laryngospasm, particularly in children

Perioperative Hyperkalemia

  • Inhaled anesthetics associated with rare increases in serum potassium levels that have resulted in cardiac arrhythmias and death in pediatric patients postoperatively
  • Patients with latent as well as overt neuromuscular disease, particularly Duchenne muscular dystrophy, appear to be most vulnerable
  • Concomitant use of succinylcholine has been associated with most, but not all, of these cases
  • Elevated serum creatinine kinase levels and, in some cases, changes in urine consistent with myoglobinuria observed
  • Despite similar presentation to malignant hyperthermia, none of the affected patients exhibited signs or symptoms of muscle rigidity or hypermetabolic state
  • Early and aggressive intervention to treat hyperkalemia and resistant arrhythmias recommended
  • Evaluation for latent neuromuscular disease recommended

General anesthetics and sedation drugs in young children and pregnant women

  • Brain development
    • Prolonged or repeated exposure may result in negative effects on fetal or young children’s brain development
    • Caution with use during surgeries or procedures in children younger than 3 years or pregnant women during their third trimester
    • Assess the risk: benefit ratio in these populations, especially for prolonged procedures (i.e., above 3 hours) or multiple procedures

Pregnancy and Lactation

  • There are no adequate and well-controlled studies in pregnant women; in animal reproduction studies, embryofetal toxicity was noted in pregnant mice exposed to 0.075% (increased post-implantation losses) and 0.3% isoflurane (increased post-implantation losses and decreased live-birth index) during organogenesis


  • Due to insufficient information regarding the excretion of isoflurane in human milk, the potential risks and benefits for each specific patient should be carefully considered before isoflurane is administered to nursing women


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