Polytrim (Polymyxin B/Trimethoprim) for Bacterial Eye Infections
Primary Indication and Use
Polytrim is FDA-approved and highly effective for treating surface ocular bacterial infections, specifically acute bacterial conjunctivitis and blepharoconjunctivitis caused by susceptible organisms including Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa. 1
Recommended Treatment Regimen
For Mild to Moderate Bacterial Conjunctivitis
- Prescribe a 5-7 day course of Polytrim as it accelerates clinical and microbiological remission, reduces transmissibility, and allows earlier return to school/work. 2
- Clinical studies demonstrate 95% of infected eyes are cured or improved within 7 days of treatment. 3
- Efficacy is comparable to other topical antibiotics including gentamicin and sulfacetamide, with cure rates of 84-89% at 2-7 days post-treatment. 4
Dosing Frequency
- Apply 1-2 drops to affected eye(s) every 3-4 hours while awake for the duration of treatment. 1
- The combination provides broad-spectrum coverage through complementary mechanisms: trimethoprim inhibits bacterial folate synthesis while polymyxin B disrupts gram-negative bacterial cell membranes. 1
Critical Limitations and When NOT to Use Polytrim
Insufficient for Severe Infections
- Polytrim alone is inadequate for gonococcal conjunctivitis, which requires systemic antibiotic therapy in addition to topical treatment. 2
- Chlamydial conjunctivitis requires systemic antibiotic therapy rather than topical treatment alone. 2
- For bacterial keratitis (corneal ulcers), fluoroquinolones are preferred first-line therapy rather than Polytrim. 5
When to Escalate or Refer
- Refer to ophthalmology immediately if patient experiences visual loss, moderate-to-severe pain, severe purulent discharge, corneal involvement, conjunctival scarring, lack of response after 3-4 days, or recurrent episodes. 2
- For severe infections with deep stromal involvement or infiltrates >2mm, aggressive fluoroquinolone therapy with loading doses every 5-15 minutes followed by hourly applications is required. 6, 5
Comparative Effectiveness
Advantages
- Trimethoprim-polymyxin B demonstrates equivalent clinical and bacteriologic effectiveness to neomycin-polymyxin B-gramicidin (Neosporin) with fewer adverse effects. 7, 8
- Well-tolerated in pediatric populations with 62% reporting very comfortable and 27% moderately comfortable during treatment. 3
- Provides excellent coverage against common pediatric pathogens (H. influenzae and S. pneumoniae). 4, 3
Limitations Compared to Fluoroquinolones
- Fluoroquinolones offer broader spectrum coverage and are preferred for more severe infections or when gram-negative resistance is suspected. 2, 5
- For MRSA infections, vancomycin may be required as Polytrim has limited activity against methicillin-resistant organisms. 2
Important Clinical Caveats
- Instruct patients to return for follow-up if no improvement occurs after 3-4 days of treatment. 2
- Systemic absorption is negligible with peak serum concentrations of only 0.03 mcg/mL trimethoprim and 1 unit/mL polymyxin B. 1
- Bacterial resistance is a growing concern; poor adherence to frequent dosing schedules contributes to treatment failure. 2
- For moderate-to-severe conjunctivitis, obtain conjunctival cultures and Gram staining before initiating treatment to guide therapy if initial treatment fails. 2