Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
OFIRMEV vs AZASAN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
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.
Azathioprine is a purine analog that inhibits purine synthesis, thereby interfering with DNA and RNA synthesis. It is metabolized to 6-mercaptopurine, which inhibits T-cell activation and proliferation, leading to immunosuppression.
Management of mild to moderate pain,Management of moderate to severe pain with adjunctive opioid analgesics,Reduction of fever
Renal transplant rejection prophylaxis,Rheumatoid arthritis,Off-label: inflammatory bowel disease (Crohn's disease, ulcerative colitis), lupus nephritis, autoimmune hepatitis, pemphigus vulgaris, myasthenia gravis, Behçet's disease, dermatomyositis, polymyositis
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.
1-3 mg/kg/day orally once daily or divided twice daily; maximum dose 2.5 mg/kg/day for rheumatoid arthritis; usual dose 50-150 mg/day.
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.
Terminal elimination half-life of azathioprine is approximately 4.5 hours (range 2–6 h), while its active metabolite 6-mercaptopurine has a half-life of 0.5–2 hours. Clinical context: Renal impairment prolongs half-life.
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.
Metabolized via xanthine oxidase and thiopurine methyltransferase (TPMT) to active and inactive metabolites. Co-administration with allopurinol inhibits xanthine oxidase, requiring dose reduction of azathioprine.
Primarily renal (85% as sulfate and glucuronide conjugates, 10% as unchanged drug). Less than 5% fecal/biliary.
Renal: 88% as 6-mercaptopurine and metabolites; biliary: <10%
10-25% bound to albumin at therapeutic concentrations.
30% bound to plasma proteins, primarily albumin.
0.8-1.0 L/kg. Indicates distribution into total body water.
0.8–1.0 L/kg, indicating extensive distribution into tissues.
100% (intravenous); not applicable for other routes as OFIRMEV is IV only.
Oral: 41–47% (azathioprine); 100% for IV administration.
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.
GFR >50 m L/min: no adjustment; GFR 10-50 m L/min: 75% of normal dose; GFR <10 m L/min: 50% of normal dose.
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.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: reduce dose by 50%; Child-Pugh Class C: contraindicated.
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).
2-3 mg/kg/day orally once daily; initial dose 1 mg/kg/day in divided doses; not recommended in children <1 year.
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.
Start at low end of dosing range (50 mg once daily); monitor renal function and adjust accordingly.
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.
Chronic immunosuppression increases the risk of malignancy, particularly lymphoma and skin cancer. Patients should be monitored for neoplasia. The drug should be used only if potential benefits outweigh risks.
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
Hematologic toxicity (leukopenia, thrombocytopenia, anemia) - monitor blood counts. Hepatotoxicity. Increased infection risk. Hypersensitivity reactions. TPMT deficiency increases toxicity risk. Monitor for pancreatitis, especially in Crohn's patients. Avoid live vaccines. Photosensitivity and skin cancer risk.
Known hypersensitivity to acetaminophen or any component of the formulation,Severe hepatic impairment or active liver disease (relative contraindication without black box)
Hypersensitivity to azathioprine or 6-mercaptopurine. Pregnancy (category D) unless potential benefit justifies risk. Lactation. Severe hepatic impairment. Myelosuppression or active infection. Concurrent use with allopurinol without dose adjustment.
No known food interactions. However, avoid excessive alcohol consumption as it may increase the risk of liver damage.
No significant food interactions. May be taken with food to reduce gastrointestinal upset. Avoid concurrent use with raw or undercooked meats to reduce risk of infection due to immunosuppression.
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.
Azathioprine is FDA Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., atrial septal defect, limb defects) in case reports, but risk may be lower than with other immunosuppressants. Second and third trimesters: Risk of fetal growth restriction, preterm delivery, and neonatal immunosuppression. Avoid unless benefit outweighs risk.
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.
Azathioprine is excreted into breast milk in small amounts; milk-to-plasma ratio approximately 0.1. Infant exposure is low, but theoretical risk of immunosuppression. Weigh benefits against risks; consider monitoring infant for leukopenia and infections.
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.
Increased clearance and reduced bioavailability during pregnancy may require dose increase to maintain therapeutic levels; monitor thiopurine metabolite levels (6-TGN, 6-MMP) and adjust accordingly. Often no change required if stable disease.
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.
Azasan (azathioprine) is a prodrug of 6-mercaptopurine. Screen for TPMT deficiency before initiation to avoid severe myelosuppression. Monitor CBC and liver function weekly for first month, then monthly. Corticosteroid-sparing agent in autoimmune conditions. Avoid live vaccines during therapy.
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.
Take exactly as prescribed; do not change dose without consulting your doctor.,Report any signs of infection, unusual bruising/bleeding, or fatigue immediately.,Avoid exposure to individuals with infections; maintain good hand hygiene.,Use effective contraception during treatment and for at least 3 months after stopping.,Do not receive live vaccines (e.g., MMR, varicella) while taking this medication.,Limit sun exposure; use sunscreen and protective clothing due to increased skin cancer risk.
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 OFIRMEV vs AZASAN, answered by our medical review team.
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.. AZASAN is a Immunosuppressant that works by Azathioprine is a purine analog that inhibits purine synthesis, thereby interfering with DNA and RNA synthesis. It is metabolized to 6-mercaptopurine, which inhibits T-cell activation and proliferation, leading to immunosuppression.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between OFIRMEV and AZASAN 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 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.. The standard adult dose of AZASAN is: 1-3 mg/kg/day orally once daily or divided twice daily; maximum dose 2.5 mg/kg/day for rheumatoid arthritis; usual dose 50-150 mg/day.. 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 OFIRMEV and AZASAN 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. 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. AZASAN is classified as Category C. Azathioprine is FDA Pregnancy Category D. First trimester: Associated with congenital anomalies (e.g., atrial septal defect, limb defects) in case reports, but risk may be lower th. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.