Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
KETOPROFEN 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 cyclooxygenase (COX-1 and COX-2) inhibitor, reducing prostaglandin synthesis; also inhibits leukotriene synthesis and has direct membrane-stabilizing 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,Ankylosing spondylitis,Mild to moderate pain,Dysmenorrhea,Acute gouty arthritis (off-label)
Mild to moderate pain,Fever
Oral: 75 mg three times daily or 50 mg four times daily; maximum 300 mg/day. Intravenous: 100 mg every 12-24 hours, infused over 15-30 minutes.
325-650 mg orally every 4-6 hours as needed; maximum 4 g/day.
Terminal elimination half-life: 2-4 hours; clinical context: short half-life allows for quick drug clearance but requires frequent dosing; may be prolonged in elderly or renal impairment.
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.
Hepatic metabolism via cytochrome P450 (CYP) enzymes, primarily CYP3A4 and CYP2C9; conjugation with glucuronic acid; minor hydrolysis to metabolites.
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: ~80% (60% as glucuronide conjugates, 20% as unchanged drug); Biliary/Fecal: ~20% via bile.
Renal: 90-95% as unchanged drug; tubular secretion and glomerular filtration. Biliary/fecal: <5%.
99% bound, primarily to albumin; free fraction increases in hypoalbuminemia.
Approximately 10-20% bound to serum albumin; extensive tissue binding.
0.1-0.2 L/kg; clinical meaning: low Vd indicates limited tissue distribution, primarily confined to plasma and extracellular fluid; higher in elderly due to increased body fat.
Apparent Vd: 0.5-0.7 L/kg (30-40 L in a 70 kg adult). Distributions into CSF and breast milk.
Oral: ~90% (capsules); Topical: 5-10% (systemic absorption); Rectal: ~80%; Intramuscular: ~100%.
Oral: 85-90% (first-pass metabolism minimal). Rectal: approximately 70-80% of oral bioavailability.
Cr Cl >50 m L/min: no adjustment. Cr Cl 25-50 m L/min: reduce dose to 50% of normal. Cr Cl <25 m L/min: avoid use or maximum 50 mg twice daily.
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: 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.
Children ≥6 months: oral 1-2 mg/kg/day divided every 6-8 hours; maximum 4 mg/kg/day. Not to exceed adult maximum.
10-15 mg/kg/dose orally every 4-6 hours; maximum 75 mg/kg/day or 4 g/day, whichever is less.
Initiate at lowest effective dose (e.g., 50 mg twice daily); use short duration; monitor renal function, GI bleeding, and cardiovascular risk.
Start at lowest effective dose (325 mg every 6 hours); avoid exceeding 3 g/day unless closely monitored.
Non-steroidal anti-inflammatory drugs (NSAIDs) cause an increased risk of serious cardiovascular thrombotic events, including myocardial infarction and stroke, which can be fatal. This risk may increase with duration of use. Patients with cardiovascular disease or risk factors may be at greater risk. NSAIDs are contraindicated for treatment of perioperative pain in the setting of coronary artery bypass graft (CABG) 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 bleeding, ulceration, and perforation; hypertension; congestive heart failure; renal toxicity; anaphylactoid reactions; serious skin reactions; hematologic toxicity; hepatic toxicity; use with caution in patients with asthma or history of GI bleeding.
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.
History of hypersensitivity to ketoprofen, aspirin, or other NSAIDs; active peptic ulcer disease; history of gastrointestinal bleeding or perforation; severe renal impairment; severe hepatic impairment; during perioperative pain in CABG surgery.
Hypersensitivity to acetaminophen or any component of the formulation; severe hepatic impairment or active liver disease.
Avoid alcohol as it increases the risk of GI bleeding. Taking with food may reduce gastrointestinal irritation but delays absorption.
Alcohol: increased risk of hepatotoxicity. Avoid concurrent use. Food: no significant interaction, but taking with food may reduce minor gastrointestinal irritation.
First trimester: Avoid due to risk of spontaneous abortion and major congenital malformations (cardiac, gastroschisis). Second trimester: Avoid if possible; associated with oligohydramnios, constriction of ductus arteriosus. Third trimester: Contraindicated due to risk of premature closure of ductus arteriosus, oligohydramnios, fetal nephrotoxicity, and periventricular hemorrhage.
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.
Compatible with caution. Small amounts excreted in breast milk (M/P ratio ~0.01-0.1). Due to risk of infant toxicity (e.g., gastrointestinal effects, renal impairment), consider alternative analgesics. Monitor infant for drowsiness, poor feeding, or rash.
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).
No specific dose adjustments recommended; use lowest effective dose for shortest duration. Increased clearance in pregnancy may necessitate dose adjustment, but avoid in third trimester. Use with caution in first and second trimesters due to maternal volume expansion and increased renal clearance.
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.
Maximum analgesic effect occurs at 50 mg oral doses; higher doses increase GI toxicity without additional pain relief. Use with caution in patients with renal impairment as ketoprofen decreases renal blood flow. Avoid use with other NSAIDs, including aspirin, due to increased ulcer risk. Ketoprofen is highly protein-bound; monitor for displacement interactions with warfarin and oral hypoglycemics.
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 recommended dose; taking more does not provide extra pain relief.,Avoid alcohol while taking this medication.,Contact your doctor immediately if you experience black or bloody stools, chest pain, or signs of an allergic reaction.,Do not take with other NSAIDs or aspirin without consulting your healthcare provider.
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.
"The concurrent use of ketoprofen, a nonsteroidal anti-inflammatory drug (NSAID), with gemeprost, a synthetic prostaglandin E1 analogue used for cervical ripening and induction of labor, may antagonize the therapeutic effects of gemeprost. Ketoprofen inhibits cyclooxygenase (COX) enzymes, reducing prostaglandin synthesis, which directly opposes the prostaglandin-mediated actions of gemeprost, such as cervical softening and uterine contraction. This pharmacodynamic antagonism can lead to decreased efficacy of gemeprost in achieving cervical ripening or inducing labor, potentially prolonging the induction-to-delivery interval or necessitating alternative interventions."
"Amodiaquine inhibits CYP2C9, the primary enzyme responsible for metabolizing ketoprofen. This results in decreased clearance and elevated plasma concentrations of ketoprofen, increasing the risk of dose-dependent adverse effects such as gastrointestinal bleeding, renal impairment, and central nervous system toxicity. Clinically, patients may experience heightened analgesic and anti-inflammatory effects, but also a greater propensity for NSAID-related toxicity."
"Lumacaftor, a strong cytochrome P450 (CYP) 3A4 inducer, significantly decreases the systemic exposure of ketoprofen, a CYP3A4 substrate, by increasing its hepatic metabolism. This interaction can lead to reduced ketoprofen plasma concentrations, potentially compromising its analgesic and anti-inflammatory efficacy. Clinically, patients may experience suboptimal pain relief or require alternative pain management strategies."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about KETOPROFEN vs ACEPHEN, answered by our medical review team.
KETOPROFEN is a NSAID that works by Non-selective cyclooxygenase (COX-1 and COX-2) inhibitor, reducing prostaglandin synthesis; also inhibits leukotriene synthesis and has direct membrane-stabilizing 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 KETOPROFEN 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 KETOPROFEN is: Oral: 75 mg three times daily or 50 mg four times daily; maximum 300 mg/day. Intravenous: 100 mg every 12-24 hours, infused over 15-30 minutes.. 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 KETOPROFEN 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. KETOPROFEN is classified as Category D/X. First trimester: Avoid due to risk of spontaneous abortion and major congenital malformations (cardiac, gastroschisis). Second trimester: Avoid if possible; associated with oligohy. 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.