Polymyxin B-Trimethoprim Ophthalmic Solution Dosing for Bacterial Conjunctivitis
Standard Dosing Regimen
For mild to moderate bacterial conjunctivitis, instill one drop in the affected eye(s) every three hours (maximum of 6 doses per day) for 7 to 10 days. 1
- This FDA-approved dosing applies to both adults and children over 2 months of age 1
- The typical treatment duration aligns with the American Academy of Ophthalmology's recommendation of a 5-7 day course for bacterial conjunctivitis 2, 3
Practical Dosing Considerations
While the FDA label specifies every 3 hours (6 times daily), clinical practice often simplifies this to four times daily for improved compliance 4, 5:
- Four-times-daily dosing has been validated in multiple clinical trials showing efficacy rates of 84-91% cure by 8-10 days 5
- The simplified regimen improves adherence without compromising outcomes 2
Comparative Efficacy and Important Limitations
Polymyxin B-trimethoprim is effective but significantly slower than fluoroquinolones like moxifloxacin:
- At 48 hours, moxifloxacin achieved 81% complete resolution versus only 44% with polymyxin B-trimethoprim (P = 0.001) 4
- By 8-10 days, polymyxin B-trimethoprim achieves 84-91% cure rates, demonstrating eventual efficacy 5, 6
- The American Academy of Ophthalmology recommends topical fluoroquinolones (moxifloxacin, levofloxacin, gatifloxacin) as more effective first-line agents against common bacterial pathogens including Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae 2
When to Use Polymyxin B-Trimethoprim
This combination remains appropriate when fluoroquinolones are unavailable or cost-prohibitive 2:
- Demonstrated efficacy against H. influenzae and S. pneumoniae in pediatric populations 5, 7
- Bacterial eradication rates of 71% by day 3-5 and 79% by day 8-10 6
- Well-tolerated with minimal adverse effects across multiple clinical trials 5, 7, 8
Critical Follow-Up Instructions
Patients should return if no improvement occurs within 3-4 days 3: