Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ACTRON vs OFIRMEV
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Acetaminophen (paracetamol) is a non-opioid analgesic and antipyretic. Its mechanism is not fully understood but involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system, reducing prostaglandin synthesis. It also modulates the endocannabinoid system and serotonergic pathways.
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.
Mild to moderate pain,Fever
Management of mild to moderate pain,Management of moderate to severe pain with adjunctive opioid analgesics,Reduction of fever
Oral: 400 mg every 4-6 hours as needed for pain; maximum 1200 mg/day.
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 2-4 hours; prolonged to 6-12 hours in elderly or renal impairment (Cr Cl <30 m L/min).
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 metabolized in the liver via glucuronidation (UGT1A1, UGT1A6, UGT1A9), sulfation (SULT1A1, SULT1A3), and oxidation (CYP2E1, CYP3A4) to form the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI), which is detoxified by glutathione.
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.
Renal: 90% as unchanged drug; biliary/fecal: 10% as metabolites.
Primarily renal (85% as sulfate and glucuronide conjugates, 10% as unchanged drug). Less than 5% fecal/biliary.
>99% bound to albumin.
10-25% bound to albumin at therapeutic concentrations.
0.1-0.2 L/kg; indicates limited extravascular distribution.
0.8-1.0 L/kg. Indicates distribution into total body water.
Oral: 70-90% (first-pass metabolism minimal); IV: 100%.
100% (intravenous); not applicable for other routes as OFIRMEV is IV only.
GFR <30 m L/min: Avoid use. GFR 30-50 m L/min: Reduce dose to 50% of normal, maximum 600 mg/day.
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 Class B: Reduce dose by 50%; maximum 600 mg/day. Child-Pugh Class C: Contraindicated.
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.
Children ≥12 years: 400 mg orally every 6-8 hours as needed; maximum 1200 mg/day. Children <12 years: Not recommended.
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).
Initiate at 200 mg every 6-8 hours; maximum 600 mg/day due to increased risk of gastrointestinal bleeding and renal impairment.
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.
Acetaminophen has been associated with cases of acute liver failure, sometimes resulting in liver transplant and death. Most cases involve use of acetaminophen at doses exceeding 4000 mg per day, often involving more than one acetaminophen-containing product.
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.
Hepatotoxicity: risk increased with chronic alcohol use, liver disease, or use of other acetaminophen-containing products. Avoid exceeding 4000 mg/day. Severe skin reactions: Stevens-Johnson syndrome, toxic epidermal necrolysis, acute generalized exanthematous pustulosis. Hypersensitivity reactions: anaphylaxis.
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
Severe hepatic impairment or active liver disease. Known hypersensitivity to acetaminophen or any component of the formulation.
Known hypersensitivity to acetaminophen or any component of the formulation,Severe hepatic impairment or active liver disease (relative contraindication without black box)
Avoid alcohol; may increase risk of GI bleeding. No specific food restrictions, but taking with food can reduce gastrointestinal irritation. Maintain adequate hydration to prevent renal impairment.
No known food interactions. However, avoid excessive alcohol consumption as it may increase the risk of liver damage.
First trimester: Based on animal studies and limited human data, possible increased risk of cardiovascular and neural tube defects. Second/third trimester: Risk of premature closure of ductus arteriosus and oligohydramnios with prolonged use. Avoid after 30 weeks gestation.
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.
Excreted in breast milk; M/P ratio 0.15. Low oral bioavailability to infant; considered compatible with breastfeeding. Monitor infant for sedation or feeding problems.
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.
Dose adjustment not typically required; however, due to increased renal clearance and volume of distribution in pregnancy, higher doses may be needed to achieve therapeutic effect. Use lowest effective dose for shortest duration.
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.
ACTRON (ketorolac tromethamine) is a nonsteroidal anti-inflammatory drug (NSAID) for short-term management of moderate to severe acute pain, typically not exceeding 5 days due to risk of GI bleeding, renal impairment, and cardiovascular events. Avoid in patients with active peptic ulcer disease, bleeding diathesis, or advanced renal disease. Monitor renal function and signs of bleeding. Use lowest effective dose for shortest duration. May cause bronchospasm in aspirin-sensitive asthma.
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.
Take with food or milk to reduce stomach upset.,Do not take for more than 5 days as prescribed; longer use increases risk of serious side effects.,Avoid alcohol while taking this medication to lower risk of stomach bleeding.,Report any signs of bleeding (e.g., black stools, vomiting blood), unusual bruising, or decreased urination.,Do not take with other NSAIDs (e.g., ibuprofen, naproxen) or aspirin without consulting your doctor.,Inform your doctor about all medications, especially blood thinners (e.g., warfarin) and diuretics.,If you have asthma, be aware of potential bronchospasm; seek immediate help if you have breathing trouble.,Not recommended during pregnancy, especially in the third trimester.
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.
No interactions on record
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ACTRON vs OFIRMEV, answered by our medical review team.
ACTRON is a NSAID that works by Acetaminophen (paracetamol) is a non-opioid analgesic and antipyretic. Its mechanism is not fully understood but involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system, reducing prostaglandin synthesis. It also modulates the endocannabinoid system and serotonergic pathways.. 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 ACTRON 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 ACTRON is: Oral: 400 mg every 4-6 hours as needed for pain; maximum 1200 mg/day.. 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 ACTRON 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. ACTRON is classified as Category C. First trimester: Based on animal studies and limited human data, possible increased risk of cardiovascular and neural tube defects. Second/third trimester: Risk of premature closur. 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.