What is the difference between tetracycline eye ointment and erythromycin eye ointment?

Generally, both tetracycline eye ointment and erythromycin eye ointment are commonly used topical antibacterial agents for ocular use. The main differences between them lie in composition, antimicrobial spectrum, indications, contraindicated populations, and common adverse reactions. A detailed analysis is as follows:

1. Composition: Tetracycline eye ointment primarily contains tetracycline, which belongs to the tetracycline class of antibiotics; erythromycin eye ointment mainly contains erythromycin, classified as a macrolide antibiotic. The distinct core pharmacological components determine differences in their mechanisms of action and indications.

2. Antimicrobial Spectrum: Tetracycline eye ointment has a broader antimicrobial spectrum, effective against Gram-positive bacteria, Gram-negative bacteria, and atypical pathogens such as chlamydia. Erythromycin eye ointment has a narrower spectrum, primarily active against Gram-positive bacteria and some Gram-negative bacteria, with moderate activity against chlamydia as well.

3. Clinical Indications: Tetracycline eye ointment is indicated for bacterial conjunctivitis, keratitis, blepharitis, and also for chlamydial infections such as trachoma. Erythromycin eye ointment is more commonly used for mild bacterial eye infections such as blepharitis and bacterial conjunctivitis, as well as for infection prophylaxis at mucocutaneous junctions.

4. Contraindicated Populations: Tetracycline eye ointment is strictly contraindicated in children under 8 years of age due to potential adverse effects on tooth and bone development. Erythromycin eye ointment has fewer contraindications—only patients with known hypersensitivity to erythromycin should avoid it—and is considered relatively safer for pediatric use, though administration should be supervised by an adult.

5. Common Adverse Reactions: Tetracycline eye ointment may cause ocular irritation, dryness, or allergic reactions, and prolonged use increases the risk of superinfection. Erythromycin eye ointment generally causes milder side effects, with occasional itching or redness of the eye, and overall better tolerability compared to tetracycline.

Both eye ointments are prescription medications and should be selected under medical guidance based on specific clinical conditions. Hands should be cleaned before application, and the tip of the tube should not touch the eye to prevent contamination. It is recommended to use the ointment within a short period after opening.