Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
Cefazolin vs ACEPHEN
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Cefazolin is a first-generation cephalosporin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), thereby inhibiting transpeptidation and disrupting peptidoglycan cross-linking. This leads to cell lysis and death primarily in susceptible gram-positive bacteria.
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.
Perioperative prophylaxis (surgical prophylaxis),Respiratory tract infections,Urinary tract infections,Skin and soft tissue infections,Biliary tract infections,Bone and joint infections,Genital infections,Septicemia,Endocarditis (off-label)
Mild to moderate pain,Fever
1-2 g IV/IM every 6-8 hours; maximum 12 g/day.
325-650 mg orally every 4-6 hours as needed; maximum 4 g/day.
1.8 hours in normal renal function; extends to 30–70 hours in end-stage renal disease (Cr Cl <10 m L/min).
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.
Cefazolin undergoes minimal hepatic metabolism; it is primarily excreted unchanged in the urine via glomerular filtration and tubular secretion. The drug is not significantly metabolized by the liver.
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: 80–90% unchanged via glomerular filtration and tubular secretion; biliary: <1%; fecal: negligible.
Renal: 90-95% as unchanged drug; tubular secretion and glomerular filtration. Biliary/fecal: <5%.
80% bound to albumin.
Approximately 10-20% bound to serum albumin; extensive tissue binding.
0.12–0.14 L/kg; approximates extracellular fluid volume, indicating low tissue penetration.
Apparent Vd: 0.5-0.7 L/kg (30-40 L in a 70 kg adult). Distributions into CSF and breast milk.
Intramuscular: 100% (complete absorption).
Oral: 85-90% (first-pass metabolism minimal). Rectal: approximately 70-80% of oral bioavailability.
Cr Cl >55 m L/min: no adjustment; Cr Cl 35-54 m L/min: 1-2 g every 8 hours; Cr Cl 11-34 m L/min: 500 mg-1 g every 12 hours; Cr Cl ≤10 m L/min: 500 mg-1 g every 24-48 hours.
GFR 10-50 m L/min: 650 mg every 6 hours; GFR <10 m L/min: 650 mg every 8 hours.
No dosage adjustment required for hepatic impairment.
Child-Pugh Class A: no adjustment; Child-Pugh Class B: maximum 2 g/day; Child-Pugh Class C: maximum 1 g/day.
50-100 mg/kg/day IV/IM divided every 8 hours; severe infections: 100 mg/kg/day divided every 6-8 hours.
10-15 mg/kg/dose orally every 4-6 hours; maximum 75 mg/kg/day or 4 g/day, whichever is less.
No specific adjustment based solely on age; dose adjustment based on renal function per Cr Cl.
Start at lowest effective dose (325 mg every 6 hours); avoid exceeding 3 g/day unless closely monitored.
No FDA black box warning.
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.
Hypersensitivity reactions (including anaphylaxis) may occur; cross-allergenicity among cephalosporins and penicillins is possible.,Clostridioides difficile-associated diarrhea (CDAD) can occur with antibiotic use.,Dosage adjustment required in patients with renal impairment due to predominantly renal elimination.,Prolonged use may result in overgrowth of nonsusceptible organisms (e.g., Candida, Pseudomonas).,Seizures may occur with high doses, especially in patients with renal impairment.
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.
Known hypersensitivity to cefazolin or any cephalosporin antibiotic,Immediate-type hypersensitivity reaction to penicillins (relative caution due to potential cross-allergenicity)
Hypersensitivity to acetaminophen or any component of the formulation; severe hepatic impairment or active liver disease.
No significant food interactions. Alcohol should be avoided during treatment and for at least 72 hours after last dose due to potential disulfiram-like reaction (nausea, vomiting, flushing).
Alcohol: increased risk of hepatotoxicity. Avoid concurrent use. Food: no significant interaction, but taking with food may reduce minor gastrointestinal irritation.
Cefazolin is classified as FDA Pregnancy Category B. Animal studies have not demonstrated fetal risk, and adequate, well-controlled studies in pregnant women are lacking. Generally considered safe throughout pregnancy; no known teratogenic effects in the first trimester. Use only if clearly needed.
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.
Cefazolin is excreted into breast milk in low concentrations (M/P ratio approximately 0.02–0.05). It is considered compatible with breastfeeding; potential for infant gut flora alteration but unlikely to cause adverse effects. Use caution in neonates with hyperbilirubinemia or glucose-6-phosphate dehydrogenase deficiency.
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).
Pregnancy increases volume of distribution and renal clearance, potentially lowering serum concentrations. Standard dosing (1–2 g every 8 hours for most infections) is generally adequate; for serious infections, consider higher doses (up to 12 g/day) or more frequent intervals (every 6 hours) in the third trimester. Adjust based on therapeutic response and renal function.
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.
Cefazolin is a first-generation cephalosporin with a short half-life; requires dose adjustment in renal impairment. Watch for cross-allergenicity in penicillin-allergic patients (approx. 10% risk). Administer parenterally only; no oral formulation available. Common surgical prophylaxis antibiotic due to good coverage of skin flora.
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.
This medication is given by injection or IV, not by mouth.,Report any signs of allergic reaction: rash, hives, itching, difficulty breathing.,May cause diarrhea; notify your doctor if severe or persistent.,Avoid alcohol while taking this medication to prevent disulfiram-like reaction.,Complete the full course as prescribed even if you feel better.
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.
"Phenprocoumon may increase the anticoagulant activities of Cefazolin."
"Warfarin may increase the anticoagulant activities of Cefazolin."
"The protein binding of Cefazolin can be decreased when combined with Phenytoin."
No interactions on record
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about Cefazolin vs ACEPHEN, answered by our medical review team.
Cefazolin is a Cephalosporin Antibiotic that works by Cefazolin is a first-generation cephalosporin antibiotic that inhibits bacterial cell wall synthesis by binding to penicillin-binding proteins (PBPs), thereby inhibiting transpeptidation and disrupting peptidoglycan cross-linking. This leads to cell lysis and death primarily in susceptible gram-positive bacteria.. 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 Cefazolin 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 Cefazolin is: 1-2 g IV/IM every 6-8 hours; maximum 12 g/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 Cefazolin 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. Cefazolin is classified as Category A/B. Cefazolin is classified as FDA Pregnancy Category B. Animal studies have not demonstrated fetal risk, and adequate, well-controlled studies in pregnant women are lacking. Generally. 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.