What is the recommended dosing schedule for Polytrim (polymyxin B 0.1%/trimethoprim 0.025%) ophthalmic solution in bacterial conjunctivitis?

Polytrim Dosing Regimen for Bacterial Conjunctivitis

For uncomplicated bacterial conjunctivitis, instill 1 drop of Polytrim (polymyxin B 0.1%/trimethoprim 0.025%) into the affected eye(s) four times daily for 7 days. 1

Standard Dosing Protocol

• Frequency: Administer 1 drop four times daily (approximately every 4-6 hours while awake) 1, 2
• Duration: Continue treatment for 7 days, even if symptoms improve earlier 1, 2
• Application technique: Remove contact lenses before instillation and do not reinsert until infection has completely resolved 3

Expected Clinical Response Timeline

• 24-48 hours: Most patients should demonstrate reduced discharge, pain, and lid edema 1
• 48 hours: Approximately 44% of patients achieve complete resolution of signs and symptoms with Polytrim 4
• 7 days: 95% of infected eyes show cure or improvement 2
• If no improvement by 48-72 hours: Return for reassessment and consider switching to a fluoroquinolone or obtaining cultures 1

Critical Dosing Considerations

Never taper below 3-4 times daily before completing the full 7-day course, as subtherapeutic dosing markedly increases antibiotic resistance risk 1, 5. The four-times-daily regimen must be maintained throughout the entire treatment period to ensure adequate tissue concentrations and prevent resistance development 1.

When Polytrim Is NOT Appropriate

Polytrim should not be used as first-line therapy in the following situations:

• Contact lens wearers: Use fluoroquinolones (ofloxacin, ciprofloxacin, moxifloxacin) instead due to higher risk of Pseudomonas aeruginosa infection 1, 3
• Severe bacterial keratitis: Requires fluoroquinolones with loading doses every 5-15 minutes, then hourly 1
• Gonococcal conjunctivitis: Requires systemic ceftriaxone 250 mg IM plus azithromycin 1 g orally, not topical therapy alone 1, 3
• Chlamydial conjunctivitis: Requires systemic azithromycin 1 g orally single dose or doxycycline 100 mg twice daily for 7 days 1, 3
• MRSA infections: Requires compounded topical vancomycin, as MRSA is resistant to both polymyxin and trimethoprim 1

Comparative Efficacy Data

While Polytrim is effective for uncomplicated bacterial conjunctivitis, moxifloxacin 0.5% three times daily achieves significantly faster cure rates (81% complete resolution at 48 hours versus 44% with Polytrim, P=0.001) 4. However, for mild cases in immunocompetent patients without contact lens use, the American Academy of Ophthalmology states there is no clinical evidence suggesting superiority of any particular antibiotic, so the most convenient or least expensive option (including Polytrim) can be selected 1.

Red Flags Requiring Immediate Ophthalmology Referral

Refer urgently if the patient develops:

• Visual loss or moderate-to-severe pain 1
• Severe purulent discharge or corneal involvement 1
• Conjunctival scarring 1
• No improvement after 3-4 days of appropriate therapy 1
• Immunocompromised state or history of HSV eye disease 1

Infection Control Counseling

Counsel patients on strict hand hygiene, avoiding eye rubbing, using separate towels, and avoiding close contact during the contagious period to prevent transmission 1. These measures are essential adjuncts to antibiotic therapy.