Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ISOFLURANE vs ACTIQ
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.
Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.
Induction and maintenance of general anesthesia,Sedation in mechanically ventilated patients (off-label)
Management of breakthrough pain in cancer patients aged 16 and older who are already receiving and tolerant to opioid therapy for their underlying persistent cancer pain
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.
200 mcg transmucosally, titrated upward as needed; initial dose for opioid-tolerant patients is 200 mcg, with additional doses possible after 15 minutes if needed. Maximum 4 doses per episode. At least 4 hours between episodes.
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.
Terminal half-life 0.83–2 hours (mean 1.3 h) in adults; note that context: transmucosal absorption leads to rapid onset but short duration; half-life is not correlated with clinical effect due to oral transmucosal route and rapid redistribution.
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 CYP3A4 to inactive metabolites (norfentanyl, despropionylfentanyl, hydroxyfentanyl) and other metabolites; <7% excreted unchanged in urine.
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 renal as metabolites (about 75% as metabolites, <10% unchanged). Fecal excretion accounts for <9%. Biliary excretion is minor.
Approximately 5-20% bound to plasma proteins, primarily albumin.
Fentanyl is 80–85% bound to plasma proteins (primarily albumin and α1-acid glycoprotein).
Volume of distribution is about 2-5 L/kg, reflecting extensive tissue distribution, especially to lipid-rich tissues like brain and fat.
Approximately 4 L/kg (range 3–6 L/kg); large Vd indicates extensive tissue distribution and redistribution contributing to short duration.
Inhalation: Bioavailability is essentially 100% for inspired drug; systemic absorption is nearly complete due to rapid pulmonary exchange.
Oral transmucosal: 50% (range 47–54%) relative to IV; variable and enhanced by rapid absorption through buccal mucosa.
No dose adjustment required in renal impairment; pharmacokinetics unaffected.
No specific GFR-based dose adjustment recommended; use with caution in severe renal impairment (Cr Cl < 30 m L/min) and consider dose reduction due to potential accumulation.
No specific dose adjustment guidelines; use with caution in severe hepatic impairment due to potential for hepatotoxicity.
Child-Pugh Class A/B: No adjustment. Child-Pugh Class C: Reduce initial dose to 100 mcg and titrate slowly; monitor closely for prolonged effects.
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.
Not approved for pediatric use; safety and efficacy not established in patients under 16 years.
Reduce concentrations by 20-50% due to increased sensitivity and decreased MAC; monitor hemodynamics closely.
Initiate at 100 mcg transmucosally; titrate slowly due to increased sensitivity and risk of respiratory depression. Monitor for adverse effects.
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.
Risk of respiratory depression, addiction, abuse, and misuse; accidental ingestion can be fatal; concomitant use with benzodiazepines or CNS depressants may cause profound sedation, respiratory depression, coma, and death; not for use in opioid non-tolerant patients; risk of neonatal opioid withdrawal syndrome with prolonged use during pregnancy; serious, life-threatening, or fatal respiratory depression may occur even at recommended doses.
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 respiratory depression; addiction, abuse, and misuse; interactions with CNS depressants; serotonin syndrome; adrenal insufficiency; severe hypotension; seizures; withdrawal; use in patients with head injuries, increased intracranial pressure, biliary tract disease, pancreatitis; risk of choking with lozenge; oral mucosal irritation; dental caries; hypokalemia; hyponatremia; use in elderly, cachectic, or debilitated patients.
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)
Significant respiratory depression; acute or severe bronchial asthma in an unmonitored setting or without resuscitative equipment; known or suspected paralytic ileus; hypersensitivity to fentanyl or any component; opioid non-tolerant patients; management of acute or postoperative pain including headache/migraine, dental pain, or emergency department use.
No specific food interactions with isoflurane. However, fasting before anesthesia is required to reduce the risk of pulmonary aspiration.
No significant food interactions. Grapefruit juice may increase fentanyl levels, but specific studies with ACTIQ are lacking. Avoid alcohol, as it may increase sedation and respiratory depression risk.
Isoflurane is not associated with major congenital malformations but may cause fetal depression, especially during third trimester. Avoid elective use until after delivery.
FDA Pregnancy Category C. First trimester: limited human data; animal studies show increased resorptions and fetal growth restriction. Second/third trimester: chronic use may cause neonatal opioid withdrawal syndrome; avoid use during labor due to risk of neonatal respiratory depression.
Minimal transfer into breast milk; M/P ratio unknown. Considered compatible with breastfeeding after single exposure; observe infant for sedation.
Excreted in breast milk; M/P ratio not established. Limited data suggest low levels, but risk of infant sedation and respiratory depression. Avoid use while breastfeeding unless potential benefit outweighs risk.
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.
Due to increased plasma volume and hepatic metabolism in pregnancy, dose requirements may increase; adjust based on clinical response and tolerance. Avoid use during labor and delivery due to risk of neonatal respiratory depression; short-term use preferred.
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.
ACTIQ is a transmucosal immediate-release fentanyl formulation indicated for breakthrough cancer pain in opioid-tolerant patients. Initiate with the lowest strength (200 mcg) and titrate upward. Avoid use in opioid-naive patients due to risk of fatal respiratory depression. Place the unit between cheek and lower gum, not sublingually. Instruct patient not to bite or suck the unit. Monitor for sedation and respiratory depression. Multiple units may be used per episode if needed, but wait at least 4 hours before next episode. Dispose of partially used units by flushing down toilet.
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.
Only use ACTIQ if you are already taking regular around-the-clock opioid pain medicine and are tolerant to opioids.,Do not use ACTIQ for short-term pain like after surgery, headache, or dental pain.,Place the unit in your cheek pouch, not under your tongue. Do not chew or suck it.,If you need more than 4 units per day, contact your doctor as your dose may need adjustment.,Store ACTIQ in a safe place away from children, as accidental ingestion can be fatal.,Dispose of unused or partially used units by flushing them down the toilet.
"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 ACTIQ, 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.. ACTIQ is a Opioid Analgesic that works by Opioid agonist; binds to mu-opioid receptors in the CNS, altering pain perception and response.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ISOFLURANE and ACTIQ depend on the specific clinical indication. These are agents from distinct pharmacological classes 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 ACTIQ is: 200 mcg transmucosally, titrated upward as needed; initial dose for opioid-tolerant patients is 200 mcg, with additional doses possible after 15 minutes if needed. Maximum 4 doses per episode. At least 4 hours between episodes.. 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 ACTIQ 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.. ACTIQ is classified as Category C. FDA Pregnancy Category C. First trimester: limited human data; animal studies show increased resorptions and fetal growth restriction. Second/third trimester: chronic use may cause. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.