Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ENFLURANE vs OFIRMEV
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Enflurane is a volatile halogenated ether that potentiates GABA-A receptor activity, inhibits NMDA receptors, and enhances glycine receptor function, leading to generalized central nervous system depression and anesthesia.
OFIRMEV (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism of action is not fully understood, but it is thought to involve inhibition of cyclooxygenase (COX) enzymes in the central nervous system, with minimal peripheral COX inhibition. It may also act on serotonergic pathways and cannabinoid receptors.
Induction and maintenance of general anesthesia,Supplement to nitrous oxide and oxygen anesthesia
Management of mild to moderate pain,Management of moderate to severe pain with adjunctive opioid analgesics,Reduction of fever
Induction: 0.5-4.5% inspired concentration; Maintenance: 0.5-3% inspired concentration with oxygen/nitrous oxide; via inhalation.
IV: 1000 mg every 6 hours or 650 mg every 4 hours; maximum single dose: 1000 mg; minimum dosing interval: 4 hours; maximum daily dose: 4000 mg.
Terminal elimination half-life is approximately 4-8 hours in adults; context: prolonged with obesity due to high lipid solubility and storage in adipose tissue.
Terminal elimination half-life is 2-3 hours in adults (2.5-3 hours in children). Clinically, dosing every 4-6 hours is needed to maintain therapeutic levels.
Primarily hepatic via cytochrome P450 (CYP2E1); approximately 2% undergoes oxidative metabolism to difluoromethoxy-difluoroacetic acid and fluoride ions; rest is excreted unchanged by lungs.
Acetaminophen is primarily metabolized in the liver via conjugation with glucuronide (50-60%) and sulfate (20-30%). A minor amount is oxidized by cytochrome P450 (CYP2E1, CYP1A2, CYP3A4) to a toxic reactive metabolite (NAPQI), which is normally detoxified by glutathione. At toxic doses, glutathione is depleted, leading to NAPQI accumulation and hepatotoxicity.
Primarily eliminated by pulmonary excretion as unchanged drug (>90%); less than 5% is metabolized via CYP2E1 to fluoride ions and other metabolites, which are renally excreted.
Primarily renal (85% as sulfate and glucuronide conjugates, 10% as unchanged drug). Less than 5% fecal/biliary.
Approximately 55-75% bound to serum proteins, primarily albumin and alpha-1-acid glycoprotein.
10-25% bound to albumin at therapeutic concentrations.
Volume of distribution at steady state (Vdss) is approximately 3.5-4.5 L/kg, indicating extensive tissue distribution and lipid solubility.
0.8-1.0 L/kg. Indicates distribution into total body water.
Inhalation: Bioavailability is essentially 100% as administered via inhalation, with rapid absorption across the alveolar-capillary barrier.
100% (intravenous); not applicable for other routes as OFIRMEV is IV only.
No specific GFR-based dose adjustment required; however, monitor for nephrotoxicity in severe renal impairment (e GFR <30 m L/min) due to potential fluoride ion accumulation.
No dose adjustment required for GFR ≥30 m L/min. For GFR <30 m L/min, extend dosing interval to every 8 hours; maximum daily dose 3000 mg.
Child-Pugh A: no adjustment; Child-Pugh B: use with caution, reduce concentration; Child-Pugh C: avoid due to risk of hepatotoxicity and altered metabolism.
Child-Pugh Class A: No adjustment. Child-Pugh Class B: Reduce total daily dose by 50% (max 2000 mg/day). Child-Pugh Class C: Contraindicated or use with extreme caution; reduce dose to 50% of standard and extend interval to every 8 hours; maximum 2000 mg/day.
Induction: 1-4% inspired concentration; Maintenance: 0.5-2% inspired concentration; adjust based on age and response.
Weight-based: <10 kg: 7.5 mg/kg/dose every 6 hours; 10-50 kg: 15 mg/kg/dose every 6 hours; >50 kg: 1000 mg every 6 hours or 650 mg every 4 hours. Maximum single dose: 15 mg/kg (up to 1000 mg); maximum daily dose: 75 mg/kg (up to 4000 mg).
Reduce inspired concentration by 25-50% due to decreased minimal alveolar concentration (MAC) and increased sensitivity; monitor hemodynamics closely.
No specific dose adjustment; consider reduced renal function. For Cr Cl <30 m L/min, extend interval to every 8 hours. Maximum daily dose: 3000 mg in frail elderly or with comorbidities.
None
Acetaminophen has been associated with cases of acute liver failure, at times resulting in liver transplant and death. Most of the cases of liver injury are associated with the use of acetaminophen at doses that exceed 4000 mg per day, and often involve more than one acetaminophen-containing product.
May cause dose-dependent respiratory and cardiovascular depression,Risk of seizures (especially with deep anesthesia or hypocarbia),Potential for hepatotoxicity (rare, but caution in patients with pre-existing liver disease),Malignant hyperthermia risk,Should not be used in patients with known sensitivity to halogenated anesthetics
Risk of serious hepatotoxicity, especially with doses >4000 mg/day or in patients with underlying liver disease,Risk of severe skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis, acute generalized exanthematous pustulosis) – discontinue at first sign of rash,Risk of hypersensitivity reactions including anaphylaxis,Use caution in patients with severe hepatic impairment, active hepatic disease, or alcoholism,Avoid concurrent use of other acetaminophen-containing products
Known hypersensitivity to enflurane or other halogenated anesthetics,Known or suspected genetic susceptibility to malignant hyperthermia,Severe hypotension or hypovolemia (relative),Prior history of hepatitis after halothane or other halogenated agents (relative)
Known hypersensitivity to acetaminophen or any component of the formulation,Severe hepatic impairment or active liver disease (relative contraindication without black box)
No specific food interactions known for enflurane. Avoid alcohol for at least 24 hours post-anesthesia as it may increase sedation and hepatotoxicity risk.
No known food interactions. However, avoid excessive alcohol consumption as it may increase the risk of liver damage.
Enflurane is not recommended during the first and second trimesters due to potential teratogenicity based on animal studies showing fetal malformations. During the third trimester, use is avoided for elective procedures as it may cause uterine relaxation and fetal depression. Risk is dose-dependent and duration-dependent.
Acetaminophen (OFIRMEV) is generally considered low risk across all trimesters. No increased risk of major congenital anomalies has been consistently demonstrated. Chronic high-dose use in third trimester may be associated with preterm birth or low birth weight. Avoid prolonged use above recommended doses.
Enflurane is excreted into breast milk in low concentrations. The M/P ratio is not well established but estimated around 0.5-1.0. Because of rapid clearance and minimal oral bioavailability, a single exposure is considered compatible with breastfeeding after waiting 24 hours. No adverse effects reported in infants.
Acetaminophen is excreted in breast milk in low concentrations (M/P ratio approximately 0.9-1.0). Considered compatible with breastfeeding; peak milk levels occur 1-2 hours after maternal dosing. Use lowest effective dose for shortest duration.
Pregnancy may decrease MAC (minimum alveolar concentration) by up to 40% due to progesterone and endogenous opioids. Dose should be reduced accordingly. No specific dose adjustment based on pharmacokinetic changes, but careful titration to effect is required.
No dose adjustment required during pregnancy. Pharmacokinetic changes in pregnancy (increased volume of distribution, clearance) may lead to lower peak concentrations but standard dosing remains effective. Maximum single dose: 1 g; maximum daily dose: 4 g.
Enflurane is a potent inhalation anesthetic that can cause dose-dependent myocardial depression and hypotension. It sensitizes the myocardium to catecholamines, increasing arrhythmia risk. Enflurane may provoke seizure activity at high concentrations or with hypocapnia. Malignant hyperthermia trigger. Use caution in patients with hepatic or renal impairment due to fluoride ion release.
OFIRMEV (acetaminophen) injection is an IV formulation of acetaminophen used for pain and fever management. It is a prodrug that requires no hepatic conversion, providing rapid onset of action. Monitor for hepatotoxicity; maximum daily dose is 4 grams in adults but lower in patients with hepatic impairment or malnutrition. Do not exceed 1 gram per dose. Hypotension and anaphylaxis have been reported. Not interchangeable with oral acetaminophen due to dose equivalency. Use with caution in patients with alcohol use disorder.
You will be unconscious and feel no pain during surgery.,You may experience nausea or shivering after waking up.,Inform your anesthesiologist if you have a personal or family history of malignant hyperthermia.,Avoid operating machinery or driving for at least 24 hours after anesthesia.,Report any unusual muscle stiffness, fever, or dark urine after surgery.
OFIRMEV is given intravenously for pain or fever.,Do not take additional acetaminophen-containing medications while receiving OFIRMEV.,Report any signs of allergic reaction (rash, itching, swelling, trouble breathing).,Seek immediate medical attention if you experience severe abdominal pain, yellowing of skin or eyes, or dark urine.,Inform your healthcare provider about all medications you are taking, especially blood thinners.
"Enflurane, a halogenated volatile anesthetic, and venlafaxine, a serotonin-norepinephrine reuptake inhibitor (SNRI), both inhibit neuronal reuptake of monoamines, leading to increased central nervous system (CNS) levels of serotonin and norepinephrine. Concurrent use may potentiate the risk of serotonin syndrome, characterized by agitation, hyperthermia, autonomic instability, and neuromuscular hyperactivity. Additionally, venlafaxine can lower the seizure threshold, while enflurane may produce epileptiform EEG activity, raising the potential for perioperative seizures."
"Enflurane is a halogenated volatile anesthetic that potentiates the effects of gamma-aminobutyric acid (GABA) at GABA-A receptors, leading to central nervous system (CNS) depression. Tiapride, a selective dopamine D2 receptor antagonist, can also cause CNS depression and prolong the QT interval. Combined use may result in additive CNS depression, increasing the risk of excessive sedation, respiratory depression, and hypotension. Additionally, both drugs can lower the seizure threshold, potentially increasing the risk of perioperative seizures."
"The combination of enflurane and levobupivacaine increases the risk of cardiotoxicity and central nervous system (CNS) toxicity. Enflurane sensitizes the myocardium to the arrhythmogenic effects of levobupivacaine, potentially leading to severe ventricular arrhythmias. Additionally, both drugs depress myocardial contractility and conduction, which may result in hypotension, bradycardia, or cardiac arrest."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ENFLURANE vs OFIRMEV, answered by our medical review team.
ENFLURANE is a Inhalational Anesthetic that works by Enflurane is a volatile halogenated ether that potentiates GABA-A receptor activity, inhibits NMDA receptors, and enhances glycine receptor function, leading to generalized central nervous system depression and anesthesia.. OFIRMEV is a Non-opioid Analgesic that works by OFIRMEV (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism of action is not fully understood, but it is thought to involve inhibition of cyclooxygenase (COX) enzymes in the central nervous system, with minimal peripheral COX inhibition. It may also act on serotonergic pathways and cannabinoid receptors.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ENFLURANE and OFIRMEV 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 ENFLURANE is: Induction: 0.5-4.5% inspired concentration; Maintenance: 0.5-3% inspired concentration with oxygen/nitrous oxide; via inhalation.. The standard adult dose of OFIRMEV is: IV: 1000 mg every 6 hours or 650 mg every 4 hours; maximum single dose: 1000 mg; minimum dosing interval: 4 hours; maximum daily dose: 4000 mg.. 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 ENFLURANE and OFIRMEV 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. ENFLURANE is classified as Category C. Enflurane is not recommended during the first and second trimesters due to potential teratogenicity based on animal studies showing fetal malformations. During the third trimester,. OFIRMEV is classified as Category C. Acetaminophen (OFIRMEV) is generally considered low risk across all trimesters. No increased risk of major congenital anomalies has been consistently demonstrated. Chronic high-dos. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.