Head-to-head clinical analysis & difference comparison: details on mechanism of action, dosing, half-life, interactions, and maternal-fetal safety.
E.E.S. 400 vs A/T/S
Clinician-reviewed, head-to-head comparison of mechanism, dosing, pharmacokinetics, and safety profiles.
Last clinically reviewed: July 2026 · OpiCalc Medical Review Team
Erythromycin, a macrolide antibiotic, binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis. At high concentrations, it may also inhibit RNA synthesis.
A/T/S (erythromycin) is a macrolide antibiotic that acts by binding to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis and bacterial growth.
Treatment of infections caused by susceptible strains of microorganisms: respiratory tract infections (including Legionnaires disease, pertussis), skin and soft tissue infections, diphtheria, syphilis, chlamydial infections, and ocular infections in neonates.,Prophylaxis of recurrent rheumatic fever.,Off-label: gastrointestinal motility disorder (as a motilin agonist).
Treatment of acne vulgaris (FDA-approved indication),Treatment of bacterial infections caused by susceptible organisms (off-label use for acne is the primary use)
Erythromycin ethylsuccinate 400 mg orally every 6 hours. For severe infections, up to 4 g/day in divided doses.
Dosing is individualized based on antithrombin activity level. For acute thrombotic events: initial bolus of 30-50 IU/kg followed by maintenance dosing to achieve target activity levels (80-120% of normal). Prophylaxis: 40-60 IU/kg every 24 hours.
1.5-2.0 hours in adults with normal renal function; may be prolonged in hepatic impairment (up to 5-6 hours) but not significantly changed in renal disease.
Terminal elimination half-life: 1–2 hours (prolonged in hepatic impairment).
Primarily metabolized in the liver via demethylation by CYP3A4; undergoes N-demethylation and hydroxylation.
Antithrombin is a glycoprotein; its metabolism involves cellular uptake and catabolism, but specific CYP450 enzymes are not involved. Degradation occurs via proteolysis and reticuloendothelial system clearance.
Primarily hepatic (biliary) excretion of unchanged drug and metabolites; approximately 2-5% renal excretion of unchanged drug; 5-15% fecal elimination.
Renal: 10-20% (active drug and metabolites); Fecal: minimal; Biliary: not significant.
70-80% bound to albumin; binding is reversible and saturable at high concentrations.
70-90% bound to serum albumin.
Approximately 0.7 L/kg (range 0.5-0.9 L/kg); indicates extensive tissue penetration including intracellular and inflammatory fluids.
0.5–0.8 L/kg (low Vd, minimal tissue penetration).
Oral (as erythromycin ethylsuccinate): approximately 30-65% (variable, reduced by food); intravenous: 100%.
Topical: 1–5% (minimal systemic absorption).
No specific dose adjustment required for renal impairment; caution with high doses in severe renal failure (Cr Cl <10 m L/min) due to potential ototoxicity.
No specific adjustment required; drug is not renally eliminated.
In hepatic impairment, reduce dose by 50-75% depending on severity. Child-Pugh Class A: no adjustment; Class B: reduce to 50% of normal dose; Class C: avoid or use with extreme caution, maximum 1 g per day.
No specific adjustment; antithrombin is produced in the liver, but exogenous replacement does not require dose adjustment in hepatic impairment.
30-50 mg/kg/day in 4 divided doses. For severe infections, up to 60-100 mg/kg/day. Maximum 2 g/day.
Dosing based on weight and antithrombin levels; typical initial dose 30-50 IU/kg, followed by maintenance to achieve target levels. Clinical trial data limited in neonates.
No specific dose adjustment; monitor for QT prolongation and hearing loss. Consider lower end of dosing range due to age-related decline in hepatic function.
No specific adjustment; use standard dosing with monitoring of antithrombin activity and bleeding risk.
Increased risk of infantile hypertrophic pyloric stenosis (IHPS) when given to neonates. Erythromycin has also been associated with prolongation of the QT interval and risk of cardiac arrhythmias, including torsades de pointes.
None.
Hepatic dysfunction, QT prolongation (risk of arrhythmia), exacerbation of myasthenia gravis, Clostridioides difficile-associated diarrhea, ototoxicity (especially with high doses or renal impairment), potential for drug interactions (CYP3A4 inhibitors/inducers).
Hypersensitivity reactions including anaphylaxis have occurred.,Prolonged use may result in overgrowth of nonsusceptible organisms including fungi.,Use with caution in patients with hepatic impairment.,Potential for QT prolongation and ventricular arrhythmias, especially with intravenous administration or concomitant drugs that prolong QT interval.
Hypersensitivity to erythromycin or any macrolide antibiotic, concomitant use with terfenadine, astemizole, cisapride, pimozide, ergotamine, or dihydroergotamine (risk of cardiac arrhythmias).
Hypersensitivity to erythromycin or any macrolide antibiotic.,Use with caution in patients with pre-existing QT prolongation or electrolyte abnormalities (relative contraindication).
Take with food to minimize gastrointestinal upset. Avoid grapefruit juice as it can increase erythromycin concentrations via CYP3A4 inhibition. No other significant food interactions.
No specific food interactions. Avoid excessive alcohol consumption as it may increase skin dryness.
FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; inadequate human studies in first trimester. No known risk of major birth defects or miscarriage. Avoid in maternal myasthenia gravis due to potential neonatal hypotonia.
FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; no adequate human studies in first trimester. Topical erythromycin has minimal systemic absorption; risk to fetus is low across all trimesters.
Compatible with breastfeeding. Erythromycin is excreted into breast milk in small amounts (M/P ratio approximately 0.5). No adverse effects reported in infants. Monitor infant for gastrointestinal disturbances or rash.
Compatible with breastfeeding. Erythromycin is excreted into breast milk in small amounts (M/P ratio approximately 0.5). Topical use results in negligible systemic exposure; unlikely to cause adverse effects in nursing infants.
No dose adjustment required. Physiologic changes in pregnancy (increased volume of distribution, renal clearance) do not necessitate dose changes for erythromycin. Standard adult dosing applies.
No dose adjustment required. Systemic absorption from topical application is minimal and not significantly altered by pregnancy-related pharmacokinetic changes.
E. E. S. 400 (erythromycin ethylsuccinate) is a macrolide antibiotic with bacteriostatic activity. It is a prodrug hydrolyzed to erythromycin base. Use with caution in patients with hepatic impairment or preexisting hearing loss. Monitor for QT prolongation, especially with concurrent use of other QT-prolonging drugs. Commonly used as an alternative in penicillin-allergic patients for respiratory tract infections. It also has prokinetic effects on the GI tract, which can be utilized in gastroparesis but may cause abdominal cramping.
A/T/S (erythromycin 2% topical solution) is indicated for acne vulgaris. Avoid contact with eyes, mouth, and mucous membranes. May cause skin dryness or irritation; use moisturizer. Effectiveness may decrease with prolonged use due to bacterial resistance. Not recommended for use with other topical erythromycin products or clindamycin to avoid antagonism.
Take this medication exactly as prescribed, usually every 6 hours or as directed.,Complete the full course even if you feel better to prevent resistance.,May cause stomach upset; taking with food can reduce GI irritation.,Avoid grapefruit juice as it may affect drug levels.,Report symptoms of liver problems (yellowing skin/eyes, dark urine) or hearing loss immediately.,Do not take with certain medications like statins or warfarin without consulting your doctor.,Use effective contraception if applicable, as erythromycin may reduce birth control pill efficacy.
Apply a thin layer to affected areas twice daily after washing.,Avoid contact with eyes, lips, and mouth; if contact occurs, rinse thoroughly with water.,May cause stinging, burning, or peeling; if irritation persists, consult your doctor.,Use sunscreen daily as this medication may increase sensitivity to sunlight.,Do not use more than prescribed; overuse may increase side effects without improving results.,Inform your doctor if you are pregnant, planning to become pregnant, or breastfeeding.,Keep away from open flames or heat sources; product is flammable.
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 E.E.S. 400 vs A/T/S, answered by our medical review team.
E.E.S. 400 is a Macrolide Antibiotic that works by Erythromycin, a macrolide antibiotic, binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis. At high concentrations, it may also inhibit RNA synthesis.. A/T/S is a Macrolide antibiotic that works by A/T/S (erythromycin) is a macrolide antibiotic that acts by binding to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis and bacterial growth.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between E.E.S. 400 and A/T/S 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 E.E.S. 400 is: Erythromycin ethylsuccinate 400 mg orally every 6 hours. For severe infections, up to 4 g/day in divided doses.. The standard adult dose of A/T/S is: Dosing is individualized based on antithrombin activity level. For acute thrombotic events: initial bolus of 30-50 IU/kg followed by maintenance dosing to achieve target activity levels (80-120% of normal). Prophylaxis: 40-60 IU/kg every 24 hours.. 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 E.E.S. 400 and A/T/S 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. E.E.S. 400 is classified as Category C. FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; inadequate human studies in first trimester. No known risk of major birth defects or miscarriage. Avoid i. A/T/S is classified as Category C. FDA Pregnancy Category B. No evidence of teratogenicity in animal studies; no adequate human studies in first trimester. Topical erythromycin has minimal systemic absorption; risk . Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.