Antibiotic Eye Drops and Ointments

Matching the antibiotic to the clinical picture

Use this guide to select a topical ophthalmic antibiotic based on the presentation, likely organisms, contact lens status, and ocular surface tolerance. The goal is to treat suspected bacterial disease promptly while avoiding unnecessarily broad coverage when a narrower option is appropriate. The medication table on this page lists brand and generic names, concentrations, typical dosing frequencies, and key cautions for each agent.

Bacterial conjunctivitis: common first-line choices

For uncomplicated bacterial conjunctivitis, several options provide effective first-line coverage:

• Polymyxin B/trimethoprim (Polytrim): a frequent first choice, especially in pediatrics. Effective against common conjunctivitis pathogens including H. influenzae and S. pneumoniae. Available generically at low cost. Typical dosing is 1 drop every 3 to 6 hours for 7 to 10 days.
• Erythromycin 0.5% ointment: practical for infants, young children, and bedtime coverage. Provides surface protection and is easy to administer. Applied as a thin ribbon to the lower conjunctival sac 2 to 4 times daily. Blurs vision, so it is often combined with a daytime drop.
• Azithromycin 1% (AzaSite): a convenient alternative with a short dosing course (1 drop twice daily for 2 days, then once daily for 5 days). The DuraSite vehicle extends contact time. Also has anti-inflammatory properties that can help in blepharitis and lid disease.

In low-risk adults without contact lens wear, an older fluoroquinolone such as ciprofloxacin or ofloxacin can be a cost-effective alternative when local resistance patterns support it.

Fluoroquinolones: older vs newer generation

Fluoroquinolones are widely used because they provide broad-spectrum coverage and good corneal penetration. The practical distinction between older and newer agents matters for higher-risk cases:

• Older generation — ciprofloxacin 0.3% (Ciloxan), ofloxacin 0.3% (Ocuflox): cost-effective for many external infections. Ciprofloxacin retains strong Pseudomonas activity and is still commonly used in corneal ulcer protocols. However, staphylococcal resistance has increased in some regions. Ciprofloxacin can leave white crystalline precipitates on corneal ulcers, which can be confused with infiltrate progression.
• Newer generation — moxifloxacin 0.5% (Vigamox), gatifloxacin 0.5% (Zymaxid), besifloxacin 0.6% (Besivance): improved gram-positive coverage including better staphylococcal activity. Moxifloxacin is preservative-free, which can improve surface tolerance. Besifloxacin uses a DuraSite mucoadhesive vehicle for extended contact time. These agents are commonly chosen for contact lens-related cases, higher-risk presentations, and perioperative prophylaxis.

Choose within the class based on local resistance trends, formulary coverage, cost, and the specific clinical scenario rather than assuming all fluoroquinolones perform identically.

Aminoglycosides, macrolides, and other agents

• Tobramycin 0.3% (Tobrex): strong gram-negative coverage and generally better tolerated than gentamicin. Commonly used for external infections and as the antibiotic component in combination products (TobraDex, Zylet). Epithelial toxicity is possible with frequent dosing and longer courses.
• Gentamicin 0.3% (Gentak, Garamycin): similar spectrum to tobramycin but more epithelial toxicity, especially with prolonged use. Less commonly chosen as a standalone agent for this reason.
• Erythromycin 0.5% ointment: remains a staple for children, bedtime coverage, and situations where ointment is preferred. Also used for chlamydial conjunctivitis in neonates (ophthalmia neonatorum prophylaxis).
• Azithromycin 1% (AzaSite): short dosing course and anti-inflammatory properties make it useful for blepharitis-associated conjunctivitis and posterior lid disease. Brand-name only, so cost can be higher.
• Bacitracin ointment: good gram-positive coverage in an ointment vehicle. Useful for lid margin disease and as an alternative when drops are not practical.

Perioperative prophylaxis

Topical antibiotics are a standard component of perioperative care for cataract surgery and other anterior segment procedures. A newer fluoroquinolone such as moxifloxacin or gatifloxacin is commonly started 1 to 3 days before surgery and continued for 1 to 2 weeks after. Some surgeons also use intracameral antibiotics at the time of surgery. The specific regimen varies by surgeon preference, institutional protocol, and local resistance patterns. When co-managing surgical patients, confirm the surgeon's preferred perioperative drop schedule and communicate clearly with the patient about the role of each medication in their regimen.

Suspected microbial keratitis

Suspected bacterial keratitis requires prompt and intensive therapy to achieve bactericidal concentrations in the cornea. Small peripheral ulcers in contact lens wearers are often started on a newer fluoroquinolone dosed every 30 to 60 minutes around the clock initially, then tapered as the ulcer responds.

Larger, central, or vision-threatening ulcers often warrant culture before starting therapy, short-interval follow-up, and co-management with a corneal specialist. Fortified antibiotics (such as fortified tobramycin and fortified vancomycin or cefazolin) from a compounding pharmacy may be appropriate depending on severity, culture results, and local protocols. The decision to culture versus treat empirically should reflect ulcer size, location, depth, anterior chamber reaction, and whether the patient has been on prior antibiotics.