Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
ETHRIL 500 vs AZITHROMYCIN
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 central analgesic and antipyretic agent whose exact mechanism is not fully understood but is thought to involve inhibition of cyclooxygenase (COX) enzymes in the brain, primarily COX-2, and activation of descending serotonergic pathways. It has weak peripheral anti-inflammatory activity.
Binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting m RNA translation and thus protein synthesis. Exhibits concentration-dependent bactericidal activity.
Mild to moderate pain,Fever
Acute bacterial exacerbations of chronic obstructive pulmonary disease due to H. influenzae, M. catarrhalis, or S. pneumoniae,Acute bacterial sinusitis due to H. influenzae, M. catarrhalis, or S. pneumoniae,Community-acquired pneumonia due to C. pneumoniae, H. influenzae, M. pneumoniae, or S. pneumoniae,Pharyngitis/tonsillitis due to S. pyogenes,Uncomplicated skin and skin structure infections due to S. aureus, S. pyogenes, or S. agalactiae,Urethritis/cervicitis due to C. trachomatis or N. gonorrhoeae,Genital ulcer disease due to H. ducreyi,Acute otitis media due to H. influenzae, M. catarrhalis, or S. pneumoniae,Prevention of disseminated M. avium complex disease in advanced HIV infection,Pertussis (off-label)
500 mg orally every 6 hours as needed for pain. Maximum daily dose: 2000 mg.
500 mg orally once daily for 3 days, or 500 mg IV once daily for at least 2 days followed by 500 mg orally to complete 7-10 days of therapy for community-acquired pneumonia. For other indications, typical adult dose is 500 mg orally on day 1 then 250 mg orally once daily on days 2-5.
Terminal elimination half-life is 2-4 hours in adults with normal renal function; prolonged to 6-12 hours in hepatic impairment or overdose.
Terminal half-life of approximately 68 hours (range 35–96 h) after multiple doses, allowing once-daily dosing and a prolonged post-antibiotic effect.
Primarily metabolized in the liver via glucuronidation and sulfation; a minor pathway via CYP2E1 (and CYP1A2, CYP3A4) produces the toxic metabolite N-acetyl-p-benzoquinone imine (NAPQI), which is normally detoxified by glutathione.
Primarily hepatic, not via cytochrome P450 system. Partially metabolized to inactive metabolites. Eliminated via biliary excretion and renal excretion (<15% unchanged).
Renal excretion of unchanged drug and glucuronide conjugate accounts for 90-95% of elimination; biliary/fecal elimination accounts for 5-10%.
Primarily biliary/fecal (approx. 50% unchanged); renal excretion accounts for about 12% of the dose.
10-25% bound to plasma proteins (albumin).
7–51% (concentration-dependent); primarily binds to albumin.
0.9-1.1 L/kg; indicates extensive distribution into body fluids including CSF.
31.1 L/kg (range 23–50 L/kg), indicating extensive tissue penetration and sequestration (e.g., WBCs, liver, lung).
Oral: 75-90% (first-pass metabolism reduces from near 100% absorption); IV: 100%; Rectal: 70-85%.
Oral: 37–40% (fasting); food may decrease absorption by ~50%.
GFR 30-50 m L/min: 500 mg every 8 hours. GFR 10-29 m L/min: 500 mg every 12 hours. GFR <10 m L/min: 500 mg every 24 hours.
No dose adjustment required for GFR ≥10 m L/min. For GFR <10 m L/min, caution advised; no specific dose recommendation, consider alternative agent.
Child-Pugh Class A: no adjustment. Child-Pugh Class B: 500 mg every 8 hours. Child-Pugh Class C: 500 mg every 12 hours.
No dose adjustment required for mild to moderate hepatic impairment (Child-Pugh class A and B). Contraindicated in severe hepatic impairment (Child-Pugh class C).
Children <2 years: not recommended. Children 2-12 years: 10-15 mg/kg/dose every 6 hours, maximum 60 mg/kg/day. Adolescents >12 years: same as adult.
For otitis media and community-acquired pneumonia: 10 mg/kg orally or IV on day 1 (max 500 mg), then 5 mg/kg (max 250 mg) once daily on days 2-5. For pharyngitis/tonsillitis: 12 mg/kg orally once daily for 5 days (max 500 mg/day).
Initiate at 500 mg every 8 hours; increase interval if needed due to reduced renal function; consider maximum daily dose of 1500 mg.
No specific dose adjustment required; use same dosing as younger adults. Monitor renal function due to age-related decline, but no modification needed unless severe renal impairment (Cr Cl <10 m L/min).
Risk of severe liver injury; do not exceed 4,000 mg per day in adults or 2,000 mg per day in patients with liver disease. Concomitant use with other acetaminophen-containing products may lead to overdose.
None.
Hepatotoxicity, especially with doses >4 g/day or in patients with hepatic impairment; risk of acute generalized exanthematous pustulosis (AGEP); serious skin reactions (Stevens-Johnson syndrome, toxic epidermal necrolysis); avoid use with alcohol or other hepatotoxic drugs.
Hepatotoxicity: hepatitis, cholestatic jaundice, hepatic necrosis, hepatic failure,QT prolongation and torsades de pointes (especially with concurrent use of other QT-prolonging agents, electrolyte abnormalities, bradycardia, or structural heart disease),Clostridioides difficile-associated diarrhea (CDAD),Aggravation of myasthenia gravis,Severe allergic reactions (angioedema, anaphylaxis, Stevens-Johnson syndrome),Infantile hypertrophic pyloric stenosis (IHPS) in neonates following oral azithromycin,Use in pregnancy: category B; avoid during breastfeeding due to potential for disruption of infant gut flora
Hypersensitivity to acetaminophen or any component; severe hepatic impairment; use of other acetaminophen-containing products concurrently.
Hypersensitivity to azithromycin, erythromycin, or any macrolide antibiotic,History of cholestatic jaundice or hepatic dysfunction associated with prior azithromycin use,Concurrent use with ergotamine or dihydroergotamine (possible ergot toxicity)
No significant food interactions. Alcohol increases risk of hepatotoxicity and should be avoided.
Food does not significantly affect absorption; can be taken with or without food. However, avoiding high-fat meals may reduce minor GI side effects. No known specific food interactions.
ETHIRIL 500 (ethyl alcohol 500 mg) is not a standard drug; assuming it refers to ethanol. Teratogenic: First trimester: Increased risk of fetal alcohol spectrum disorders (FASD) including craniofacial abnormalities, growth deficiency, and neurodevelopmental deficits with chronic heavy use. Second trimester: Risk of spontaneous abortion and intrauterine growth restriction (IUGR). Third trimester: Risk of preterm birth, low birth weight, and neonatal withdrawal syndrome. No safe threshold established.
FDA Category B. No evidence of teratogenicity in animal studies; limited human data show no increased risk of major malformations. First trimester: No significant association with birth defects. Second/third trimester: No reported fetal harm from short-term use for infections like chorioamnionitis. Use only if clearly needed.
Ethanol is excreted into breast milk. Milk-to-plasma ratio approximately 1.0. Peak milk levels occur 30-60 minutes after ingestion. Chronic heavy use may impair infant motor development and cause sedation. Avoid breastfeeding within 2 hours of alcohol consumption; excessive use contraindicated.
Azithromycin is excreted into breast milk in low amounts. M/P ratio approximately 0.2-0.6. Relative infant dose estimated at 2-6% of maternal weight-adjusted dose. Generally considered compatible with breastfeeding; monitor infant for diarrhea or rash.
No therapeutic dosing; ethanol is not indicated in pregnancy. If used inadvertently, pharmacokinetic changes: increased volume of distribution may lower peak alcohol concentration, but no dose adjustment recommendation. Avoidance is critical.
No dose adjustment required for pregnancy. Standard adult dosing (500 mg on day 1, then 250 mg daily for 4 days) is appropriate. Note: Pregnancy may increase volume of distribution, but pharmacokinetic studies suggest no significant decrease in AUC; no need for dose increase.
ETHRIL 500 (acetaminophen 500 mg) is hepatotoxic in overdose; maximum daily dose is 4 g in adults, but reduce to 2 g in patients with hepatic impairment, alcoholism, or malnutrition. Administer N-acetylcysteine for overdose within 8 hours for best efficacy.
Monitor for QTc prolongation especially in patients with preexisting cardiac conditions or those on other QT-prolonging drugs. Azithromycin has a long half-life (68 hours) allowing for shorter treatment courses. Use with caution in hepatic impairment; consider alternative in severe liver disease. Not recommended for pneumonia in patients with bacteremia due to increased mortality risk. Administer on an empty stomach or with food if GI upset occurs; however, absorption is unaffected by food.
Do not exceed 4 g (eight 500 mg tablets) per day.,Avoid alcohol while taking this medication.,Do not combine with other acetaminophen-containing products.,Seek immediate medical attention if overdose is suspected.,Take with or without food as needed.
Take exactly as prescribed; do not skip doses or stop early even if you feel better.,Do not take antacids containing aluminum or magnesium within 2 hours before or after this medication.,Report any signs of liver problems (nausea, vomiting, dark urine, jaundice) or severe diarrhea (watery or bloody) immediately.,Azithromycin may cause dizziness; avoid driving or operating machinery until you know how it affects you.,Inform your doctor if you have a history of QT prolongation, heart rhythm problems, or electrolyte imbalances.,Store at room temperature away from moisture and heat; discard any unused liquid after 10 days.
No interactions on record
"Azithromycin, a macrolide antibiotic, is known to prolong the QT interval by blocking cardiac potassium channels (specifically IKr), which can lead to torsades de pointes. Mifepristone also poses a risk of QT prolongation, likely via similar mechanisms. Coadministration may result in additive QTc prolongation, increasing the risk of life-threatening ventricular arrhythmias, especially in patients with preexisting cardiac conditions or electrolyte disturbances."
"Lumiracoxib is a selective COX-2 inhibitor primarily metabolized by CYP2C9 and to a lesser extent by CYP3A4. Azithromycin, a macrolide antibiotic, is a known inhibitor of CYP3A4. Concomitant use may decrease the metabolism of azithromycin, leading to increased plasma concentrations and potential toxicity, such as QT prolongation and hepatotoxicity. Elevated azithromycin levels can also enhance its antibacterial effects but raise safety concerns."
"Azithromycin, a macrolide antibiotic, inhibits the cardiac potassium channel encoded by hERG (human Ether-à-go-go-Related Gene), leading to prolonged cardiac repolarization and increased risk of QTc interval prolongation. Arformoterol, a long-acting beta-2 agonist, can also prolong the QTc interval via beta-adrenergic receptor-mediated effects on cardiac ion channels. Concurrent use may result in additive QTc prolongation, predisposing patients to potentially fatal ventricular arrhythmias such as torsades de pointes."
Explore head-to-head clinical comparisons of other medications in the same therapeutic classes.
Common clinical questions about ETHRIL 500 vs AZITHROMYCIN, answered by our medical review team.
ETHRIL 500 is a Macrolide Antibiotic that works by Acetaminophen (paracetamol) is a central analgesic and antipyretic agent whose exact mechanism is not fully understood but is thought to involve inhibition of cyclooxygenase (COX) enzymes in the brain, primarily COX-2, and activation of descending serotonergic pathways. It has weak peripheral anti-inflammatory activity.. AZITHROMYCIN is a Macrolide Antibiotic that works by Binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting m RNA translation and thus protein synthesis. Exhibits concentration-dependent bactericidal activity.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between ETHRIL 500 and AZITHROMYCIN depend on the specific clinical indication. These are both Macrolide Antibiotic agents and are not directly interchangeable by dose. A physician or clinical pharmacist should guide any therapeutic switching decisions.
The standard adult dose of ETHRIL 500 is: 500 mg orally every 6 hours as needed for pain. Maximum daily dose: 2000 mg.. The standard adult dose of AZITHROMYCIN is: 500 mg orally once daily for 3 days, or 500 mg IV once daily for at least 2 days followed by 500 mg orally to complete 7-10 days of therapy for community-acquired pneumonia. For other indications, typical adult dose is 500 mg orally on day 1 then 250 mg orally once daily on days 2-5.. 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 ETHRIL 500 and AZITHROMYCIN 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. ETHRIL 500 is classified as Category C. ETHIRIL 500 (ethyl alcohol 500 mg) is not a standard drug; assuming it refers to ethanol. Teratogenic: First trimester: Increased risk of fetal alcohol spectrum disorders (FASD) in. AZITHROMYCIN is classified as Category A/B. FDA Category B. No evidence of teratogenicity in animal studies; limited human data show no increased risk of major malformations. First trimester: No significant association with . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.