How is polymyxin B and trimethoprim used to treat conjunctivitis?

Polymyxin B/Trimethoprim for Bacterial Conjunctivitis

Polymyxin B/trimethoprim ophthalmic solution is an effective first-line treatment for acute bacterial conjunctivitis and blepharoconjunctivitis, providing broad-spectrum coverage against common pathogens including Staphylococcus aureus, Streptococcus pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa. 1, 2

FDA-Approved Indications

• Polymyxin B/trimethoprim is FDA-approved for surface ocular bacterial infections, specifically acute bacterial conjunctivitis and blepharoconjunctivitis caused by susceptible organisms. 1, 2
• The combination provides coverage against both gram-positive organisms (S. aureus, S. epidermidis, S. pneumoniae, S. viridans) and gram-negative organisms (H. influenzae, P. aeruginosa). 1, 2

Dosing and Administration

• Standard dosing: Instill 1 drop four times daily for 5-7 days for mild to moderate bacterial conjunctivitis. 3, 4
• The American Academy of Ophthalmology recommends a 5-7 day course of broad-spectrum topical antibiotics to accelerate clinical and microbiological remission, reduce transmissibility, and allow earlier return to school/work. 3

Clinical Efficacy

• Clinical studies demonstrate that 95% of infected eyes show cure or improvement within 7 days of treatment with polymyxin B/trimethoprim. 5
• At 2-7 days after completion of therapy, 84% of patients achieve complete cure with an additional 9% showing improvement. 6
• The combination is equally effective as gentamicin and sulfacetamide for treating bacterial conjunctivitis caused by H. influenzae and S. pneumoniae. 6

Comparative Effectiveness

• Polymyxin B/trimethoprim demonstrates equivalent efficacy to neomycin-polymyxin B-gramicidin for eliminating bacteria in conjunctivitis and blepharitis. 4
• However, fluoroquinolones (moxifloxacin) achieve significantly faster symptom resolution: 81% complete resolution at 48 hours versus 44% with polymyxin B/trimethoprim. 7
• The American Academy of Ophthalmology recommends choosing the most convenient or least expensive antibiotic for mild bacterial conjunctivitis, as no clinical evidence suggests superiority of any particular agent for uncomplicated cases. 3

When to Use Fluoroquinolones Instead

• Reserve fluoroquinolones for moderate to severe bacterial conjunctivitis with copious purulent discharge, pain, and marked inflammation. 3
• Contact lens wearers require fluoroquinolones due to higher risk of Pseudomonas infection. 3
• Suspected resistant organisms warrant fluoroquinolone use rather than polymyxin B/trimethoprim. 3

Important Limitations and Contraindications

• Polymyxin B/trimethoprim alone is insufficient for gonococcal conjunctivitis, which requires systemic antibiotic therapy (ceftriaxone) in addition to topical treatment. 3
• Chlamydial conjunctivitis requires systemic antibiotics (azithromycin or doxycycline) rather than topical treatment alone. 3
• Polymyxin B/trimethoprim is not recommended for bacterial keratitis, which requires fluoroquinolones with better corneal penetration. 3

Follow-Up and Monitoring

• Patients should return for follow-up if no improvement is seen after 3-4 days of treatment. 3
• At follow-up, perform interval history, visual acuity measurement, and slit-lamp biomicroscopy. 3
• Most patients should show reduced discharge, pain, and lid edema within 24-48 hours; if no improvement by 48 hours, consider switching to a fluoroquinolone or obtaining cultures. 8

When to Refer to Ophthalmology

• Refer to an ophthalmologist for visual loss, moderate or severe pain, severe purulent discharge, corneal involvement, conjunctival scarring, lack of response to therapy, or recurrent episodes. 3
• Hospitalization may be necessary for severe gonococcal conjunctivitis and is mandatory for neonatal conjunctivitis. 3

Safety Profile

• Polymyxin B/trimethoprim is well-tolerated with minimal adverse events reported in clinical studies. 5
• When adverse events occur, they are typically transient and of mild-to-moderate intensity. 5
• Patients report being very comfortable or moderately comfortable in 89% of cases. 5

Special Prophylactic Use

• For Boston keratoprosthesis patients, polymyxin B/trimethoprim is recommended as lifelong antimicrobial prophylaxis (daily instillation) to prevent vision-threatening endophthalmitis. 9
• High-risk keratoprosthesis patients (autoimmune conditions, monocular) require dual coverage with vancomycin combined with polymyxin B/trimethoprim. 9