What is the recommended dosage and treatment duration for Polytrim (polymyxin B and trimethoprim) regimen for bacterial eye infections?

Polytrim (Polymyxin B/Trimethoprim) Dosing Regimen

Recommended Dosage and Duration

For mild to moderate bacterial conjunctivitis, instill one drop in the affected eye(s) every 3 hours (maximum 6 doses per day) for 7 to 10 days. 1, 2

Standard Dosing Protocol

• Frequency: One drop every 3 hours while awake 1, 2
• Maximum daily doses: 6 drops per day 1, 2
• Treatment duration: 7 to 10 days for complete eradication 1, 2
• Pediatric dosing: Same regimen as adults for children over 2 months of age 2

Clinical Context and Positioning

Polytrim is appropriate for mild to moderate bacterial conjunctivitis but is NOT first-line therapy for severe infections or bacterial keratitis. 3, 4

• The American Academy of Ophthalmology recommends topical fluoroquinolones (azithromycin, moxifloxacin, gatifloxacin) as first-line treatment for bacterial conjunctivitis due to superior efficacy 3
• For bacterial keratitis, topical fluoroquinolones are strongly preferred over Polytrim, as they achieve better tissue penetration and broader coverage 5, 4
• The WHO endorses topical gentamicin, tetracycline, or ofloxacin as alternatives for bacterial conjunctivitis, with Polytrim not specifically highlighted in recent international guidelines 5, 3

Comparative Efficacy Data

Polytrim demonstrates slower clinical resolution compared to newer fluoroquinolones:

• Moxifloxacin 0.5% three times daily achieved complete resolution in 81% of patients at 48 hours versus only 44% with Polytrim four times daily (p=0.001) 6
• Despite slower onset, Polytrim still achieved 95% cure or improvement rates within 7 days in pediatric studies 7
• Physicians rated Polytrim's overall efficacy as excellent or good in 96% of cases, though this reflects older comparative standards 7

Important Clinical Caveats

Do not use Polytrim for:

• Severe bacterial keratitis (deep stromal involvement, infiltrates >2mm, or hypopyon present) - these require fluoroquinolones with loading doses every 5-15 minutes, then hourly 5, 4
• Contact lens-related infections - higher risk of Pseudomonas, which requires fluoroquinolone coverage 5
• Gonococcal or chlamydial conjunctivitis - these require systemic antibiotics (ceftriaxone for gonococcal, azithromycin or doxycycline for chlamydial) 3
• Lesions close to the limbus - consider adding systemic antibiotics 5, 4

Monitoring and Modification

• Most patients should show reduced discharge, pain, and lid edema within 24-48 hours 5
• If no improvement by 48 hours, consider switching to a fluoroquinolone or obtaining cultures 5
• Avoid tapering below 3-4 times daily before completing the full course, as subtherapeutic dosing increases resistance risk 5
• Prolonged use beyond 10 days can cause medication toxicity and corneal epithelial damage 5

Safety Profile

• Polytrim is well-tolerated with minimal adverse events reported in clinical trials 7, 8
• Transient mild-to-moderate discomfort occurs but is generally acceptable 7
• No significant safety differences compared to chloramphenicol in head-to-head studies 9