What is the appropriate dosing schedule for a 1 mg/mL polymyxin B/trimethoprim ophthalmic solution?

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Last updated: September 22, 2026 • View editorial policy

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Polymyxin B/Trimethoprim 1mg/mL Ophthalmic Solution Dosing

For a 1 mg/mL polymyxin B/trimethoprim ophthalmic solution, instill one drop in the affected eye(s) every 3 hours (maximum 6 doses per day) for 7-10 days in both adults and children over 2 months of age. 1

Standard Dosing Regimen

The FDA-approved dosing for polymyxin B/trimethoprim ophthalmic solution is straightforward:

  • Frequency: Every 3 hours while awake
  • Maximum daily doses: 6 drops per day
  • Duration: 7-10 days for mild to moderate bacterial conjunctivitis
  • Pediatric dosing: Identical to adult dosing for children >2 months old 1

Clinical Context and Application

This combination targets the most common bacterial pathogens causing conjunctivitis. The trimethoprim component (1 mg/mL) is effective against gram-positive organisms including Staphylococcus aureus, Streptococcus pneumoniae, and Haemophilus influenzae, while polymyxin B (10,000 units/mL in standard formulations) provides gram-negative coverage, particularly against Pseudomonas aeruginosa 1, 2.

For mild bacterial conjunctivitis, the 2024 AAO guidelines indicate that topical antibiotics provide earlier clinical resolution compared to placebo, with benefits most apparent in days 2-5 of treatment 3. The choice of antibiotic is typically empiric, and polymyxin B/trimethoprim remains cost-effective with no evidence suggesting superiority of any particular broad-spectrum antibiotic for uncomplicated cases 3.

Important Clinical Caveats

  • Follow-up timing: Patients should return in 3-4 days if no improvement is noted 3
  • Not for severe infections: Moderate to severe bacterial conjunctivitis with copious purulent discharge requires culture-guided therapy and potentially different antibiotics 3
  • Gonococcal conjunctivitis: Requires systemic antibiotic therapy, not topical treatment alone 3
  • Systemic absorption: Minimal with peak serum concentrations of only 0.03 mcg/mL trimethoprim and 1 unit/mL polymyxin B 1

The evidence supports polymyxin B/trimethoprim as clinically equivalent to newer fluoroquinolones for uncomplicated bacterial conjunctivitis, with one 2013 trial showing non-inferior clinical cure rates of 96% versus 95% for moxifloxacin at 7-10 days 4.

References

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.