Is Polytrim Okay for Treating Bacterial Infections?
Yes, Polytrim (polymyxin B sulfate and trimethoprim ophthalmic solution) is an effective and well-tolerated treatment for bacterial eye infections, particularly acute bacterial conjunctivitis and blepharoconjunctivitis, and remains a cost-effective first-line option compared to fluoroquinolones.
FDA-Approved Indications
Polytrim is specifically indicated for surface ocular bacterial infections caused by susceptible organisms including 1:
- Staphylococcus aureus and Staphylococcus epidermidis
- Streptococcus pneumoniae and Streptococcus viridans
- Haemophilus influenzae
- Pseudomonas aeruginosa
The combination works through complementary mechanisms: trimethoprim blocks bacterial folate synthesis while polymyxin B disrupts gram-negative bacterial cell membranes 1.
Clinical Efficacy Evidence
Comparative Effectiveness
Polytrim demonstrates equivalent or superior efficacy to other topical antibiotics:
A 2013 randomized controlled trial in 124 children with acute conjunctivitis showed clinical cure rates of 96% for polymyxin B-trimethoprim versus 95% for moxifloxacin at 7-10 days, with no statistically significant difference (noninferiority P ≤ 0.01) 2.
A multicentre trial of 230 patients found Polytrim was significantly more effective than chloramphenicol (P = 0.03) in reducing signs and symptoms of bacterial conjunctivitis 3.
Polytrim showed equivalent efficacy to neomycin-polymyxin B-gramicidin with no significant differences in clinical outcomes 3.
Pediatric Use
Polytrim is particularly well-suited for children:
A survey of 472 children treated by pediatricians showed 95% of infected eyes were cured or improved within 7 days 4.
Overall efficacy was rated excellent or good in 96% of cases (76% excellent, 20% good) 4.
Patient comfort was rated very comfortable or moderately comfortable in 89% of cases (62% very comfortable, 27% moderately comfortable) 4.
Safety Profile
Polytrim has an excellent safety record:
Adverse events are rare, transient, and mild-to-moderate in intensity 4.
Peak serum concentrations after topical application are minimal (0.03 mcg/mL trimethoprim, 1 unit/mL polymyxin B), indicating negligible systemic absorption 1.
Multiple clinical trials report very few adverse reactions with good tolerability 3, 5.
Cost-Effectiveness Consideration
Use of polymyxin B-trimethoprim for conjunctivitis would result in significant cost savings compared with fluoroquinolones while maintaining equivalent clinical efficacy 2. This makes it an economically rational first-line choice.
Special Clinical Context: Boston Keratoprosthesis Prophylaxis
For patients with Boston keratoprosthesis implants, lifelong antimicrobial prophylaxis with daily polymyxin B combined with trimethoprim is recommended as standard prophylaxis to prevent vision-threatening endophthalmitis 6. High-risk patients (autoimmune conditions, monocular) require dual coverage with vancomycin combined with polymyxin B/trimethoprim 6.
Limitations and When NOT to Use
Polytrim should not be used for:
- Systemic infections (topical ophthalmic use only) 1
- Infections outside the eye
- Patients with known hypersensitivity to trimethoprim or polymyxin B 1
Important caveat: While polymyxin B is mentioned in guidelines for treating carbapenem-resistant gram-negative bacilli, this refers to intravenous polymyxin formulations, not the topical ophthalmic Polytrim product 6. The two should not be confused—Polytrim is exclusively for ocular surface infections.
Practical Prescribing
Standard dosing: Instill 1 drop in affected eye(s) every 3 hours (maximum 6 doses per day) for 7-10 days 1, 4.
Clinical response should be evident by days 4-6, with complete resolution typically by days 7-10 4, 2.