Polymyxin B Dosing for Corneal Abrasion
For uncomplicated traumatic corneal abrasions, use polymyxin B-containing ophthalmic solution (typically polymyxin B/trimethoprim) 1 drop every 3 hours (maximum 6 doses daily) for 7-10 days. 1
Dosing Regimen
The FDA-approved dosing for polymyxin B ophthalmic preparations is straightforward 1:
- Frequency: 1 drop every 3 hours
- Maximum daily doses: 6 drops per day
- Duration: 7-10 days for mild to moderate infections
This regimen applies to prophylactic use in corneal abrasions, which the 2024 AAO guidelines strongly recommend for trauma-related abrasions 2.
Clinical Context and Rationale
Prophylactic antibiotics are indicated for all traumatic corneal abrasions, particularly when treatment begins within 24 hours of injury 2. The AAO Bacterial Keratitis Preferred Practice Pattern explicitly states that broad-spectrum topical antibiotics should be prescribed for any patient with corneal abrasion following trauma to prevent both bacterial and fungal infection 2.
Key Treatment Principles:
- Topical drops are preferred over ointments for most cases, as ointments lack adequate corneal penetration 2
- Do NOT patch the eye in trauma-related or contact lens-associated abrasions—this increases infection risk 2
- Do NOT use therapeutic contact lenses in contact lens-associated abrasions due to increased keratitis risk 2
Special Considerations
Contact Lens-Related Abrasions
If the abrasion is contact lens-related, polymyxin B alone is insufficient. You must use an antipseudomonal agent (fluoroquinolone preferred) because Pseudomonas aeruginosa is a major pathogen in this setting 3. Polymyxin B does have antipseudomonal activity 1, but fluoroquinolones are the standard of care for contact lens-related cases.
Combination Products
Polymyxin B is typically formulated with trimethoprim (polymyxin B/trimethoprim) for broader gram-positive and gram-negative coverage 1. This combination provides:
- Polymyxin B: Gram-negative coverage, especially Pseudomonas aeruginosa
- Trimethoprim: Gram-positive coverage including Staphylococcus species and Streptococcus species
Evidence Quality and Limitations
The evidence supporting antibiotic prophylaxis in corneal abrasions is surprisingly weak. A 2025 Cochrane review found very low certainty evidence for antibiotic use, with one study paradoxically showing antibiotics may increase infection risk (RR 1.32) 4. However, this conflicts with clinical practice guidelines and real-world experience.
Despite weak research evidence, the AAO guidelines strongly recommend prophylactic antibiotics based on clinical consensus and the potential catastrophic consequences of bacterial keratitis 2. The risk-benefit analysis favors treatment in real-world practice, even if randomized trials haven't definitively proven benefit.
Common Pitfalls
Using ointment as monotherapy: While convenient for bedtime dosing, ointments don't penetrate adequately for primary treatment 2
Patching the eye: This is contraindicated and increases infection risk 2
Inadequate follow-up: Patients with abrasions >4mm, worsening symptoms, or vision changes require re-evaluation at 24 hours 3
Wrong antibiotic choice for contact lens wearers: Must use antipseudomonal coverage 3
Adjunctive Pain Management
While not part of the polymyxin B regimen, consider: