What is the typical treatment duration with polymixin B (Polymyxin B) and trimethoprim eye drops for bacterial bilateral conjunctivitis?

Treatment Duration for Bacterial Bilateral Conjunctivitis with Polymyxin B-Trimethoprim Eye Drops

Treat bacterial bilateral conjunctivitis with polymyxin B-trimethoprim eye drops for 7 to 10 days, instilling one drop every 3 hours (maximum 6 doses daily) for mild to moderate infections. 1

FDA-Approved Dosing Regimen

The FDA-approved labeling for polymyxin B-trimethoprim ophthalmic solution specifies:

• Duration: 7 to 10 days 1
• Frequency: Every 3 hours (maximum 6 doses per day) 1
• This regimen applies to both adults and children over 2 months of age 1

Guideline-Based Treatment Duration

The American Academy of Ophthalmology recommends a 5 to 7 day course of broad-spectrum topical antibiotics applied 4 times daily for mild bacterial conjunctivitis 2. This creates a slight discrepancy with the FDA labeling, which extends treatment up to 10 days.

Reconciling the Evidence

• The FDA label represents the approved dosing from clinical trials and should guide initial prescribing, particularly since it specifies the exact dosing interval (every 3 hours) rather than a fixed number of daily doses 1
• Clinical studies using polymyxin B-trimethoprim have employed various durations:
  • 10-day treatment courses showed 84% cure rates at 2-7 days post-treatment 3
  • 7-day treatment courses demonstrated 95% cure or improvement rates 4
  • Some studies used as few as 5 days with three-times-daily dosing 5

Clinical Outcomes by Treatment Duration

By 48 hours: Expect approximately 44% complete resolution of signs and symptoms with polymyxin B-trimethoprim 6

By 7 days: Expect 95% of cases to be cured or improved 4

By 2-7 days post-treatment completion: Expect 84% cure rate and 83% bacteriologic eradication 3

Important Clinical Considerations

When to Extend Treatment Beyond 7 Days

• Moderate to severe cases with copious purulent discharge, pain, and marked inflammation may benefit from the full 10-day course 2
• Incomplete response at 5-7 days warrants continuation to the full 10-day duration 1

Common Pitfall to Avoid

Do not prescribe shorter courses than 5 days. While bacterial conjunctivitis may be self-limited, topical antibacterial therapy provides earlier clinical and microbiological remission, reduces transmissibility, and allows earlier return to school for children 2. Inadequate treatment duration risks incomplete bacterial eradication and potential resistance development 2.

When This Regimen May Be Insufficient

• Gonococcal conjunctivitis requires systemic antibiotics in addition to topical therapy, as corneal perforation can occur within 24-48 hours 7
• Chlamydial conjunctivitis requires systemic therapy rather than topical treatment alone 2, 7
• MRSA infections may require compounded topical vancomycin rather than polymyxin B-trimethoprim 2

Practical Algorithm

1. Start with 7-day course for typical bilateral bacterial conjunctivitis 1, 4
2. Reassess at 48-72 hours - expect significant improvement 6
3. If improving, complete 7 days 4
4. If inadequate response or severe presentation, extend to 10 days 1
5. If no improvement by 5-7 days, obtain cultures and consider alternative diagnoses or resistant organisms 2