Polymyxin B/Trimethoprim (Polytrim) for Bacterial Conjunctivitis
For a 70-year-old with mild bacterial conjunctivitis (pink eye), prescribe polymyxin B/trimethoprim (Polytrim) ophthalmic solution, 1 drop four times daily for 5-7 days—it is an effective, inexpensive, broad-spectrum option that remains a first-line choice for uncomplicated cases. 1, 2
Why Polytrim is the Right Choice
The 2024 AAO Conjunctivitis Preferred Practice Pattern explicitly states that for mild bacterial conjunctivitis, "the most convenient or least expensive option can be selected; there is no clinical evidence suggesting the superiority of any particular antibiotic" over a 5-7 day course 1. This guideline-level recommendation directly supports using Polytrim as your go-to agent.
FDA-Approved Indications and Coverage
Polytrim is FDA-approved specifically for acute bacterial conjunctivitis and covers the most common pathogens 2:
- Staphylococcus aureus and S. epidermidis (via trimethoprim)
- Streptococcus pneumoniae (via trimethoprim)
- Haemophilus influenzae (via trimethoprim)
- Pseudomonas aeruginosa (via polymyxin B)
This dual-mechanism combination provides both gram-positive and gram-negative coverage, which is exactly what you need for empiric therapy 2.
Clinical Evidence Supporting Polytrim
Equivalent Efficacy to Newer Agents
A 2013 randomized controlled trial in children demonstrated that polymyxin B-trimethoprim achieved a 96% clinical cure rate at 7-10 days, statistically non-inferior to moxifloxacin (95%) 3. The study explicitly concluded that "use of polymyxin B-trimethoprim for the treatment of conjunctivitis would result in significant cost savings compared with fluoroquinolones" 3.
Important Caveat About Speed of Resolution
One 2008 study found moxifloxacin resolved symptoms faster at 48 hours (81% vs 44%) 4. However, this speed difference becomes clinically irrelevant by day 7 when cure rates equalize 3. For a 70-year-old with uncomplicated conjunctivitis, the slower initial response is acceptable given the cost savings and equivalent final outcome.
Historical Track Record
Multiple older studies confirm Polytrim's effectiveness, with a 1995 survey showing 95% of infected eyes cured or improved within 7 days 5, and a 1984 study demonstrating equal effectiveness to neomycin-polymyxin-gramicidin 6.
Dosing Instructions
Prescribe: 1 drop in affected eye(s) four times daily for 5-7 days 2, 7
Instruct the patient to:
- Continue the full course even if symptoms improve
- Return in 3-4 days if no improvement 1
- Avoid contact lens wear during treatment
When NOT to Use Polytrim
Do not use Polytrim for moderate-to-severe conjunctivitis characterized by:
- Copious purulent discharge
- Significant pain
- Marked inflammation
- Suspected gonococcal infection (requires systemic ceftriaxone) 1
In these cases, obtain cultures and consider broader coverage or systemic therapy 1.
Cost-Effectiveness Consideration
The guideline acknowledges that "although there are no data supporting the cost-effectiveness of using antibiotics in mild bacterial conjunctivitis, the shortened morbidity associated with their use makes choice of therapy an individual decision" 1. Given that Polytrim is among the least expensive topical antibiotics and performs equivalently to fluoroquinolones, it represents optimal value 3, 7.
Alternative Inexpensive Options
If Polytrim is unavailable, other guideline-recommended inexpensive alternatives include 7:
- Polymyxin/gramicidin
- Sulfacetamide
However, Polytrim's broader gram-negative coverage (including Pseudomonas via polymyxin B) makes it preferable 2.