Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ISOFLURANE vs FORANE
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Isoflurane is a general inhalation anesthetic that acts as a positive allosteric modulator of GABA-A receptors and glycine receptors, and inhibits excitatory receptors such as NMDA and AMPA receptors. It potentiates inhibitory neurotransmission and depresses excitatory neurotransmission, leading to anesthesia, amnesia, and muscle relaxation.
Enhances GABA-A receptor activity and inhibits glutamate receptors, leading to neuronal hyperpolarization and anesthesia.
Induction and maintenance of general anesthesia,Sedation in mechanically ventilated patients (off-label)
Induction and maintenance of general anesthesia,Sedation for mechanical ventilation in intensive care
Induction: 1-3% in oxygen or oxygen/nitrous oxide mixture via inhalation; Maintenance: 0.5-2% in oxygen or oxygen/nitrous oxide mixture via inhalation.
Induction: 0.5-3% inspired; Maintenance: 0.5-2% inspired.
Terminal elimination half-life is approximately 2.5 to 5 hours. Context: The context-sensitive half-time varies with duration of anesthesia; for short procedures (<1 hour), half-life is about 2-4 minutes, but for prolonged anesthesia, it can be 30-60 minutes due to redistribution from fat stores.
Context-sensitive half-life: 2-5 minutes after short exposure; prolonged to 30-60 minutes after prolonged administration due to accumulation in fat and muscle. Terminal elimination half-life: 0.5-1 hour.
Isoflurane undergoes minimal metabolism (approximately 0.2%) primarily via hepatic cytochrome P450 enzymes (CYP2E1), leading to the production of inorganic fluoride and trifluoroacetic acid. The major route of elimination is via exhalation as unchanged drug.
Primarily hepatic via CYP2E1; also undergoes glucuronidation and defluorination.
Primarily eliminated via exhalation through the lungs (>99%). Less than 1% undergoes hepatic metabolism to trifluoroacetic acid and fluoride ions, which are excreted renally.
Primarily exhaled unchanged via lungs (>95%); <5% metabolized in liver to fluoride ions and other metabolites, which are excreted renally.
Approximately 5-20% bound to plasma proteins, primarily albumin.
~40% bound to plasma proteins (mainly albumin).
Volume of distribution is about 2-5 L/kg, reflecting extensive tissue distribution, especially to lipid-rich tissues like brain and fat.
Vd: 1.5-2.0 L/kg, reflecting distribution to highly perfused tissues (brain, heart, liver, kidneys) and subsequent redistribution to muscle and fat.
Inhalation: Bioavailability is essentially 100% for inspired drug; systemic absorption is nearly complete due to rapid pulmonary exchange.
100% via inhalation.
No dose adjustment required in renal impairment; pharmacokinetics unaffected.
No adjustment required.
No specific dose adjustment guidelines; use with caution in severe hepatic impairment due to potential for hepatotoxicity.
Use with caution; reduce dose in severe hepatic impairment (Child-Pugh C).
Induction: 1.5-3% in oxygen or oxygen/nitrous oxide mixture; Maintenance: 0.5-2% in oxygen or oxygen/nitrous oxide mixture; titrate to effect.
Induction: 1-4% inspired; Maintenance: 0.5-2% inspired.
Reduce concentrations by 20-50% due to increased sensitivity and decreased MAC; monitor hemodynamics closely.
Reduce inspired concentrations by 25-50% due to increased sensitivity.
Because isoflurane is a potent halogenated anesthetic, it may cause malignant hyperthermia, a life-threatening condition characterized by hypermetabolism, muscle rigidity, tachycardia, and hyperthermia. Immediate treatment with dantrolene and discontinuation of triggering agents is essential.
None
Risk of malignant hyperthermia,Respiratory depression,Hypotension and myocardial depression,Elevated intracranial pressure,Hepatic injury (rare),Nephrotoxicity due to fluoride ion (rare),QT interval prolongation,Use with caution in patients with coronary artery disease
Risk of malignant hyperthermia,Respiratory depression,Hypotension,Hepatotoxicity with repeated use or in susceptible patients,Nephrotoxicity due to fluoride ions
Known or suspected susceptibility to malignant hyperthermia,Prior history of unexplained jaundice or fever after isoflurane administration,Concurrent use of entacapone (increased risk of intraoperative myocardial depression)
Known hypersensitivity to isoflurane or other halogenated agents,Known or suspected genetic susceptibility to malignant hyperthermia
No specific food interactions with isoflurane. However, fasting before anesthesia is required to reduce the risk of pulmonary aspiration.
No specific food interactions are documented for isoflurane. However, patients should follow standard preoperative fasting guidelines (e.g., NPO for 8 hours prior to elective surgery) to reduce aspiration risk during anesthesia.
Isoflurane is not associated with major congenital malformations but may cause fetal depression, especially during third trimester. Avoid elective use until after delivery.
FORANE (isoflurane) is classified as FDA Category C. In first trimester, animal studies show fetal malformations at high doses; human data insufficient. Second and third trimesters: known to cause dose-dependent maternal hypotension and uterine relaxation, which may reduce placental perfusion; use only if clearly needed.
Minimal transfer into breast milk; M/P ratio unknown. Considered compatible with breastfeeding after single exposure; observe infant for sedation.
Isoflurane is excreted into breast milk in minimal amounts; M/P ratio is approximately 0.85. After inhalational anesthesia, the concentration in milk is low and rapidly cleared. The American Academy of Pediatrics considers it compatible with breastfeeding. However, it is recommended to discard milk for 24 hours post-procedure due to sedation and potential metabolites.
No dose adjustment required for pregnancy per se; however, MAC decreases by about 25-40% during pregnancy due to hormonal changes and increased progesterone. Use lowest effective dose.
No specific dose adjustment is required for pregnancy, but due to increased volume of distribution and decreased protein binding, a slightly lower dose may achieve desired anesthetic depth. Maintenance of uterine perfusion pressure is critical; avoid hypotension. The minimum alveolar concentration (MAC) is decreased by approximately 25% in pregnancy.
Isoflurane is a halogenated ether anesthetic. It causes dose-dependent hypotension primarily through vasodilation. It is not recommended for induction in pediatrics due to pungency and airway irritability. Malignant hyperthermia trigger. Use with caution in patients with elevated intracranial pressure as it can increase cerebral blood flow. Monitor end-tidal CO2 and volatile agent concentration.
FORANE (isoflurane) is a potent inhalational anesthetic with rapid onset and offset due to low blood-gas solubility. It causes dose-dependent respiratory depression and hypotension via peripheral vasodilation. Monitor end-tidal CO2 and arterial blood pressure closely. Avoid in patients with known or suspected malignant hyperthermia susceptibility. Use a calibrated vaporizer to deliver precise concentrations (1-3% for induction, 0.5-2% for maintenance).
You will receive isoflurane gas to keep you asleep and pain-free during surgery.,You may experience shivering or nausea after awakening; tell your nurse if severe.,Do not eat or drink for the time instructed before surgery to prevent aspiration.,If you have a personal or family history of malignant hyperthermia, inform your anesthesiologist immediately.,Arrange for a ride home after surgery as isoflurane can impair coordination and judgment for up to 24 hours.
This medication is for hospital use only and will be administered by an anesthesia provider.,You may experience drowsiness, dizziness, or confusion after waking from anesthesia.,Do not drive or operate machinery for at least 24 hours after receiving this drug.,Inform your doctor if you have a personal or family history of malignant hyperthermia.,Report any muscle rigidity, fever, or dark urine to your healthcare provider immediately.
"Telithromycin, a macrolide antibiotic, prolongs the QT interval by blocking the rapid component of the delayed rectifier potassium current (IKr). Isoflurane, a volatile anesthetic, also prolongs the QT interval via inhibition of IKr and other cardiac ion channels. The combination may lead to additive or synergistic QT prolongation, increasing the risk of torsades de pointes, a potentially fatal ventricular arrhythmia, especially in patients with other risk factors such as hypokalemia, bradycardia, or pre-existing cardiac disease."
"Isoflurane, a volatile halogenated anesthetic, potentiates the cardiodepressant and arrhythmogenic effects of levobupivacaine, a long-acting amide local anesthetic, by inhibiting myocardial calcium channels and β-adrenergic responsiveness. This additive negative inotropic and chronotropic effect increases the risk of hypotension, bradycardia, and potentially life-threatening ventricular arrhythmias during combined use. Additionally, isoflurane may delay levobupivacaine metabolism by reducing hepatic blood flow, prolonging systemic exposure and toxicity."
"The combination of isoflurane and thiamylal results in synergistic CNS depression and enhanced negative inotropic and vasodilatory effects on the cardiovascular system. Isoflurane potentiates the barbiturate-induced suppression of myocardial contractility and baroreceptor reflexes, leading to a heightened risk of hypotension, bradycardia, and reduced cardiac output. Clinically, patients may experience profound anesthesia, prolonged recovery, and hemodynamic instability, especially during induction and maintenance of anesthesia."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ISOFLURANE vs FORANE, answered by our medical review team.
ISOFLURANE is a Inhalational Anesthetic that works by Isoflurane is a general inhalation anesthetic that acts as a positive allosteric modulator of GABA-A receptors and glycine receptors, and inhibits excitatory receptors such as NMDA and AMPA receptors. It potentiates inhibitory neurotransmission and depresses excitatory neurotransmission, leading to anesthesia, amnesia, and muscle relaxation.. FORANE is a Inhalational Anesthetic that works by Enhances GABA-A receptor activity and inhibits glutamate receptors, leading to neuronal hyperpolarization and anesthesia.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ISOFLURANE and FORANE depend on the specific clinical indication. These are both Inhalational Anesthetic agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ISOFLURANE is: Induction: 1-3% in oxygen or oxygen/nitrous oxide mixture via inhalation; Maintenance: 0.5-2% in oxygen or oxygen/nitrous oxide mixture via inhalation.. The standard adult dose of FORANE is: Induction: 0.5-3% inspired; Maintenance: 0.5-2% inspired.. Dosing should always be individualized based on indication, renal and hepatic function, age, and other patient factors.
No direct drug-drug interaction has been formally documented between ISOFLURANE and FORANE in current clinical databases. However, individual patient risk factors including other medications, organ function, and comorbidities should always be evaluated by a qualified healthcare provider.
The maternal-fetal safety profiles differ. ISOFLURANE is classified as Category C. Isoflurane is not associated with major congenital malformations but may cause fetal depression, especially during third trimester. Avoid elective use until after delivery.. FORANE is classified as Category C. FORANE (isoflurane) is classified as FDA Category C. In first trimester, animal studies show fetal malformations at high doses; human data insufficient. Second and third trimesters. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.