Polymyxin B Ophthalmic Dosing for Bacterial Conjunctivitis
For bacterial conjunctivitis, instill one drop of polymyxin B ophthalmic solution in the affected eye(s) every 3 hours (maximum 6 doses per day) for 7-10 days. 1
Standard Dosing Regimen
- The FDA-approved dosing for polymyxin B ophthalmic solution is 1 drop every 3 hours (up to 6 times daily) for 7-10 days in mild to moderate infections 1
- When polymyxin B is combined with trimethoprim (the most common formulation), the standard regimen is 1 drop four times daily for 5-7 days 2, 3
Clinical Efficacy Considerations
- Polymyxin B/trimethoprim is significantly less effective than newer fluoroquinolones like moxifloxacin, with only 44% of patients achieving complete resolution at 48 hours compared to 81% with moxifloxacin 4
- Despite lower speed of efficacy, polymyxin B/trimethoprim remains a viable option endorsed by the American Academy of Ophthalmology for uncomplicated bacterial conjunctivitis when cost or availability is a concern 2, 3
- Clinical cure rates by 3-5 days with polymyxin-containing regimens are approximately 47-62%, with most patients (84-91%) cured by 8-10 days 5, 6
Important Limitations and When NOT to Use Polymyxin B
- Polymyxin B/trimethoprim alone is insufficient for gonococcal conjunctivitis, which requires systemic ceftriaxone plus azithromycin in addition to any topical therapy 3, 7
- Chlamydial conjunctivitis requires systemic antibiotics (azithromycin or doxycycline in adults; erythromycin in children), as topical therapy alone is inadequate 2, 3
- Contact lens wearers with suspected Pseudomonas infection should receive fluoroquinolones rather than polymyxin B 3
- MRSA conjunctivitis may require compounded topical vancomycin, as polymyxin B has limited activity against resistant gram-positive organisms 2, 3
Follow-Up and Red Flags
- Patients should return for evaluation if no improvement occurs after 3-4 days of treatment 2, 3
- Immediate ophthalmology referral is indicated for visual loss, moderate to severe pain, severe purulent discharge, corneal involvement, or lack of response to therapy 2, 3
- Obtain conjunctival cultures and Gram staining before treatment if gonococcal infection is suspected based on severe purulent discharge 2, 3
Special Populations
- In children, polymyxin B/trimethoprim can be used four times daily for 7 days, though fluoroquinolones are preferred first-line agents for children >12 months 7
- For neonatal conjunctivitis, systemic therapy is mandatory and topical polymyxin B alone is never sufficient 2, 7
Practical Considerations
- Polymyxin B/trimethoprim is generally well-tolerated with minimal adverse effects reported in clinical trials 4, 8
- The four-times-daily dosing may reduce compliance compared to newer agents dosed three times daily 4
- Povidone-iodine 1.25% ophthalmic solution may be equally effective as polymyxin B/neomycin/gramicidin and can be considered when antibiotics are unavailable 9