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 AZASITE
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.
Azasite (azithromycin ophthalmic solution) is a macrolide antibiotic that binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis.
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 bacterial conjunctivitis caused by susceptible organisms
Erythromycin ethylsuccinate 400 mg orally every 6 hours. For severe infections, up to 4 g/day in divided doses.
1 drop of 1% ophthalmic solution to each affected eye twice daily (approximately 12 hours apart) for 2 days, then once daily for 5 days.
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: 68-72 hours; facilitates once-weekly dosing for trachoma.
Primarily metabolized in the liver via demethylation by CYP3A4; undergoes N-demethylation and hydroxylation.
Not significantly metabolized; primarily excreted unchanged in bile and urine.
Primarily hepatic (biliary) excretion of unchanged drug and metabolites; approximately 2-5% renal excretion of unchanged drug; 5-15% fecal elimination.
Primarily hepatic/biliary (fecal) as unchanged drug: ~70% fecal, ~20% renal (mostly unchanged), ~0.5% urinary as metabolites.
70-80% bound to albumin; binding is reversible and saturable at high concentrations.
~50-60% bound to plasma proteins (primarily albumin).
Approximately 0.7 L/kg (range 0.5-0.9 L/kg); indicates extensive tissue penetration including intracellular and inflammatory fluids.
Vd: ~100 L/kg (extensive tissue penetration; not meaningful for topical use; systemic Vd based on IV data).
Oral (as erythromycin ethylsuccinate): approximately 30-65% (variable, reduced by food); intravenous: 100%.
Ophthalmic: negligible systemic absorption (<10% of topical dose) due to low corneal permeability and dilution by tears.
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 dosage adjustment required for ophthalmic use.
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 dosage adjustment required for ophthalmic use.
30-50 mg/kg/day in 4 divided doses. For severe infections, up to 60-100 mg/kg/day. Maximum 2 g/day.
Safety and efficacy in pediatric patients have not been established; limited data available.
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 dosage adjustment recommended; use same dosing as for adults.
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).
Prolonged use may result in overgrowth of nonsusceptible organisms,Contact lens should not be worn during treatment,Do not inject subconjunctivally or introduce into the anterior chamber
Hypersensitivity to erythromycin or any macrolide antibiotic, concomitant use with terfenadine, astemizole, cisapride, pimozide, ergotamine, or dihydroergotamine (risk of cardiac arrhythmias).
Hypersensitivity to azithromycin, erythromycin, or any macrolide antibiotic,Hypersensitivity to any component of the formulation
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 clinically significant food interactions. Administer with or without food as per dosing instructions.
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.
Azasite (azithromycin ophthalmic) is classified as FDA Pregnancy Category B. Systemic absorption is minimal after ophthalmic administration. No teratogenic effects have been observed in animal studies at doses up to 200 mg/kg/day (systemic). Limited human data; risk is considered low. First trimester: unlikely to cause major malformations. Second and third trimesters: no specific risks identified.
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.
Azithromycin is excreted into human milk after systemic administration; the M/P ratio is approximately 0.90. After ophthalmic administration, systemic absorption is minimal, resulting in negligible exposure to the infant. Considered compatible with breastfeeding; use with caution if eye drops are applied multiple times daily.
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 is necessary for ophthalmic use in pregnancy. Pharmacokinetic changes in pregnancy (increased volume of distribution, altered clearance) do not significantly affect topical ocular drug levels due to negligible systemic absorption.
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.
Azasite (azithromycin ophthalmic solution) is a macrolide antibiotic used for bacterial conjunctivitis. Shake well before each use. Avoid contact with contact lenses during treatment. Do not use for more than 14 days. Monitor for signs of hypersensitivity.
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.
Shake the bottle well before each use.,Wash hands before and after application.,Do not touch the dropper tip to any surface.,Remove contact lenses before use; do not reinsert during treatment.,Instill the prescribed number of drops in the affected eye(s).,Avoid wearing eye makeup during treatment.,Finish the entire course of medication even if symptoms improve.,Report any worsening, itching, or swelling to your doctor.
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 AZASITE, 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.. AZASITE is a Macrolide Antibiotic that works by Azasite (azithromycin ophthalmic solution) is a macrolide antibiotic that binds to the 50S ribosomal subunit of susceptible bacteria, inhibiting protein synthesis.. They differ in pharmacokinetic profiles, FDA-approved indications, and side effect profiles.
Potency comparisons between E.E.S. 400 and AZASITE 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 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 AZASITE is: 1 drop of 1% ophthalmic solution to each affected eye twice daily (approximately 12 hours apart) for 2 days, then once daily for 5 days.. 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 AZASITE 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. AZASITE is classified as Category C. Azasite (azithromycin ophthalmic) is classified as FDA Pregnancy Category B. Systemic absorption is minimal after ophthalmic administration. No teratogenic effects have been observ. Always consult a maternal-fetal medicine specialist before taking either drug during pregnancy or lactation.