Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
Ibuprofen vs ACEPHEN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Non-selective inhibition of cyclooxygenase (COX-1 and COX-2), reducing prostaglandin synthesis, leading to anti-inflammatory, analgesic, and antipyretic effects.
ACEPHEN (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system, particularly COX-2, reducing prostaglandin synthesis. It has weak peripheral COX inhibition and minimal anti-inflammatory effect.
Rheumatoid arthritis,Osteoarthritis,Mild to moderate pain,Dysmenorrhea,Fever reduction,Juvenile idiopathic arthritis,Patent ductus arteriosus closure (off-label),Pericarditis (off-label),Gout (off-label)
Mild to moderate pain,Fever
200-800 mg orally every 6-8 hours; maximum 3200 mg/day.
325-650 mg orally every 4-6 hours as needed; maximum 4 g/day.
Terminal elimination half-life is 2-4 hours; no accumulation with repeated dosing in normal renal function.
Terminal elimination half-life: 1.0-1.5 hours in adults with normal renal function. Prolonged to 2-5 hours in hepatic impairment or elderly; requires dose adjustment in severe hepatic disease.
Primarily hepatic via CYP2C9 (major) and CYP2C8 (minor); also undergoes glucuronidation. Metabolites are inactive.
Acetaminophen is primarily metabolized in the liver via glucuronidation (UGT1A1, UGT1A6, UGT1A9) and sulfation (SULT1A1, SULT1A3). A minor fraction is oxidized by cytochrome P450 enzymes (CYP2E1, CYP1A2, CYP3A4) to a reactive toxic metabolite (NAPQI), which is normally detoxified by conjugation with glutathione.
Renal excretion of conjugated metabolites (about 90% as glucuronide and sulfate conjugates, <10% as unchanged drug); minor biliary/fecal elimination (<5%).
Renal: 90-95% as unchanged drug; tubular secretion and glomerular filtration. Biliary/fecal: <5%.
99% bound primarily to albumin.
Approximately 10-20% bound to serum albumin; extensive tissue binding.
0.1-0.2 L/kg; low Vd consistent with high protein binding and limited tissue distribution.
Apparent Vd: 0.5-0.7 L/kg (30-40 L in a 70 kg adult). Distributions into CSF and breast milk.
Oral: 80-100% (rapidly and completely absorbed).
Oral: 85-90% (first-pass metabolism minimal). Rectal: approximately 70-80% of oral bioavailability.
GFR 30-60 m L/min: no adjustment needed; GFR 15-29 m L/min: 200 mg every 12 hours; GFR <15 m L/min: avoid use.
GFR 10-50 m L/min: 650 mg every 6 hours; GFR <10 m L/min: 650 mg every 8 hours.
Child-Pugh A: no adjustment; Child-Pugh B: use with caution, reduce dose by 50%; Child-Pugh C: avoid use.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: maximum 2 g/day; Child-Pugh Class C: maximum 1 g/day.
5-10 mg/kg/dose orally every 6-8 hours; maximum 40 mg/kg/day.
10-15 mg/kg/dose orally every 4-6 hours; maximum 75 mg/kg/day or 4 g/day, whichever is less.
Start at lowest effective dose (200 mg every 8-12 hours); maximum 400 mg/day due to increased risk of GI bleeding and renal impairment.
Start at lowest effective dose (325 mg every 6 hours); avoid exceeding 3 g/day unless closely monitored.
NSAIDs cause an increased risk of serious cardiovascular thrombotic events, including myocardial infarction and stroke, which can be fatal. Risk may increase with duration of use. Contraindicated for treatment of perioperative pain in coronary artery bypass graft surgery.
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 4,000 milligrams per day, and often involve more than one acetaminophen-containing product.
Cardiovascular thrombotic events,Gastrointestinal ulceration, bleeding, perforation,Hypertension,Heart failure exacerbation,Renal toxicity (including acute renal failure, interstitial nephritis),Anaphylactoid reactions,Serious skin reactions (e.g., Stevens-Johnson syndrome, toxic epidermal necrolysis),Hematologic effects (e.g., anemia, prolonged bleeding time),Hepatic impairment,Asthmatic reactions in aspirin-sensitive patients
Risk of severe liver injury with doses >4000 mg/day; use caution with hepatic impairment, chronic alcoholism, malnutrition, or concomitant hepatotoxic drugs; avoid exceeding recommended dose; limit use to 10 days for pain or 3 days for fever unless directed by physician; serious skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis) have occurred.
Hypersensitivity to ibuprofen or any NSAID,History of asthma, urticaria, or allergic-type reactions after taking aspirin or other NSAIDs,Perioperative pain in coronary artery bypass graft surgery,Active gastrointestinal bleeding, ulceration, or perforation,Advanced renal disease,Pregnancy (third trimester),Severe heart failure (NYHA class IV),Cerebrovascular bleeding
Hypersensitivity to acetaminophen or any component of the formulation; severe hepatic impairment or active liver disease.
Alcohol: increases GI irritation and bleeding risk. Grapefruit juice: no significant interaction. High-fat meals may delay absorption but do not reduce overall bioavailability.
Alcohol: increased risk of hepatotoxicity. Avoid concurrent use. Food: no significant interaction, but taking with food may reduce minor gastrointestinal irritation.
First trimester: NSAID use associated with increased risk of miscarriage and congenital anomalies (e.g., cardiac defects, gastroschisis). Second trimester: Avoid due to potential oligohydramnios and fetal renal impairment. Third trimester: Contraindicated; risk of premature ductus arteriosus closure, persistent pulmonary hypertension, oligohydramnios, and fetal nephrotoxicity.
Pregnancy Category C. First trimester: potential risk of neural tube defects and orofacial clefts (limited human data, animal studies show embryotoxicity). Second and third trimesters: NSAID exposure associated with oligohydramnios, premature ductus arteriosus constriction, and fetal renal impairment. Avoid in third trimester.
Ibuprofen is compatible with breastfeeding. M/P ratio approximately 0.6–1.1. Transfer into breast milk is low; relative infant dose <1% maternal weight-adjusted dose. Preferred NSAID during lactation due to short half-life and low infant exposure.
Excreted into breast milk in low concentrations (M/P ratio approximately 0.10). Considered compatible with breastfeeding; however, use lowest effective dose for shortest duration given potential for neonatal adverse effects (e.g., thrombocytopenia, renal dysfunction).
Physiological changes in pregnancy (increased volume of distribution, renal clearance) may reduce serum concentrations. However, no specific dose adjustment is routinely recommended. Use lowest effective dose for shortest duration. Avoid in third trimester.
No standard dose adjustments recommended; however, due to increased plasma volume and metabolism in pregnancy, higher doses may be required to achieve therapeutic effect. Avoid near term.
Ibuprofen has a ceiling effect for analgesia; exceeding 400 mg per dose provides minimal additional pain relief but increases GI and cardiovascular risks. Avoid use in patients with severe renal impairment (Cr Cl <30 m L/min) or active peptic ulcer disease. In asthma patients, note that NSAIDs can trigger bronchospasm in approximately 10% of aspirin-sensitive individuals. For acute pain, a single dose of 400-800 mg is effective; for chronic use, use the lowest effective dose for the shortest duration. Ibuprofen is highly protein-bound and may displace warfarin, increasing INR; monitor closely.
ACEPHEN (acetaminophen) is commonly used for mild to moderate pain and fever. Avoid exceeding 4 g/day in adults to prevent hepatotoxicity. In patients with hepatic impairment, reduce maximum daily dose to 2 g. Consider acetylcysteine for overdose. Onset of action is 15-30 minutes orally.
Take with food or milk to reduce stomach upset.,Do not exceed 1200 mg per day without a doctor's approval; maximum OTC dose is 400 mg every 4-6 hours.,Avoid alcohol while taking ibuprofen to reduce the risk of stomach bleeding.,Stop taking and contact your doctor if you experience signs of stomach bleeding: black or bloody stools, vomiting blood, or severe abdominal pain.,Ibuprofen can increase risk of heart attack or stroke, especially with long-term use or high doses; discuss your cardiovascular risk with your doctor.,Do not take ibuprofen if you are pregnant (especially in the third trimester) unless directed by your doctor, as it can harm the unborn baby.
Do not exceed 4000 mg (4 grams) in 24 hours.,Avoid drinking alcohol while taking this medication.,Do not combine with other products containing acetaminophen.,Take with food if stomach upset occurs.,Seek immediate medical help if you experience symptoms of liver damage: yellowing of skin/eyes, dark urine, severe abdominal pain.
"Concomitant use of Ibuprofen (a nonsteroidal anti-inflammatory drug, NSAID) and Methylprednisolone (a systemic corticosteroid) synergistically increases the risk of gastrointestinal (GI) ulceration, bleeding, and perforation due to additive inhibition of prostaglandin synthesis and mucosal protection. Additionally, Ibuprofen may potentiate the immunosuppressive effects of Methylprednisolone, elevating infection risk. This interaction can lead to serious clinical outcomes, including acute GI hemorrhage, perforation, and impaired wound healing."
"The combination of olopatadine, an antihistamine with sedative properties, and ibuprofen, a nonsteroidal anti-inflammatory drug (NSAID), may result in additive central nervous system (CNS) depression, leading to increased sedation, dizziness, and impaired psychomotor function. Ibuprofen can inhibit the metabolism of olopatadine via competition for hepatic CYP450 enzymes, potentially elevating olopatadine plasma concentrations and prolonging its systemic effects. Clinically, patients may experience exacerbated drowsiness, reduced alertness, and increased risk of falls or accidents, especially in the elderly or those with compromised hepatic function."
"Ibuprofen, a nonsteroidal anti-inflammatory drug (NSAID), can decrease the metabolism of pioglitazone, a thiazolidinedione antidiabetic agent, by inhibiting cytochrome P450 2C8 (CYP2C8) enzyme activity. This inhibition elevates plasma concentrations of pioglitazone, potentially enhancing its hypoglycemic effects and increasing the risk of adverse reactions such as edema, weight gain, and heart failure exacerbation. Clinically, concomitant use may lead to improved glycemic control but also raises concerns for dose-dependent toxicities, necessitating careful monitoring and possible dose adjustment of pioglitazone."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about Ibuprofen vs ACEPHEN, answered by our medical review team.
Ibuprofen is a NSAID that works by Non-selective inhibition of cyclooxygenase (COX-1 and COX-2), reducing prostaglandin synthesis, leading to anti-inflammatory, analgesic, and antipyretic effects.. ACEPHEN is a Non-Opioid Analgesic that works by ACEPHEN (acetaminophen) is a para-aminophenol derivative with analgesic and antipyretic activity. Its mechanism involves inhibition of cyclooxygenase (COX) enzymes in the central nervous system, particularly COX-2, reducing prostaglandin synthesis. It has weak peripheral COX inhibition and minimal anti-inflammatory effect.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between Ibuprofen and ACEPHEN 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 Ibuprofen is: 200-800 mg orally every 6-8 hours; maximum 3200 mg/day.. The standard adult dose of ACEPHEN is: 325-650 mg orally every 4-6 hours as needed; maximum 4 g/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 Ibuprofen and ACEPHEN 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. Ibuprofen is classified as Category D/X. First trimester: NSAID use associated with increased risk of miscarriage and congenital anomalies (e.g., cardiac defects, gastroschisis). Second trimester: Avoid due to potential o. ACEPHEN is classified as Category C. Pregnancy Category C. First trimester: potential risk of neural tube defects and orofacial clefts (limited human data, animal studies show embryotoxicity). Second and third trimest. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.