What about using polymyxin (Polymyxin B) for bacterial conjunctivitis treatment?

Polymyxin B for Bacterial Conjunctivitis

Polymyxin B (combined with trimethoprim) is an effective and appropriate first-line treatment option for mild to moderate bacterial conjunctivitis, though fluoroquinolones like moxifloxacin achieve faster clinical resolution. 1, 2

FDA-Approved Indications

Polymyxin B/trimethoprim ophthalmic solution is FDA-approved for surface ocular bacterial infections, including acute bacterial conjunctivitis and blepharoconjunctivitis, caused by susceptible organisms including Staphylococcus aureus, Staphylococcus epidermidis, Streptococcus pneumoniae, Haemophilus influenzae, and Pseudomonas aeruginosa. 3

Clinical Efficacy and Comparative Effectiveness

Mild Bacterial Conjunctivitis

• For mild bacterial conjunctivitis, polymyxin B/trimethoprim is clinically effective with cure rates of 95-96% by day 7-10, which is non-inferior to moxifloxacin. 4
• The American Academy of Ophthalmology recommends choosing the most convenient or least expensive antibiotic for mild cases, as no clinical evidence suggests superiority of any particular agent. 1
• Polymyxin B/trimethoprim achieves clinical cure in approximately 72% of patients by days 4-6, compared to 77% with moxifloxacin. 4

Speed of Resolution

• Moxifloxacin demonstrates significantly faster symptom resolution, with 81% complete resolution at 48 hours versus 44% with polymyxin B/trimethoprim (P = .001). 2
• Despite slower initial response, final cure rates are equivalent between the two agents by day 7-10. 4

Cost-Effectiveness

• Polymyxin B/trimethoprim offers significant cost savings compared to fluoroquinolones while maintaining equivalent final clinical outcomes. 4
• This makes it a rational first-line choice when cost is a consideration and rapid resolution is not critical. 1, 4

Mechanism of Action

Polymyxin B increases bacterial cell membrane permeability by interacting with phospholipid components, providing bactericidal activity against gram-negative organisms, particularly Pseudomonas aeruginosa. 3 Trimethoprim blocks tetrahydrofolic acid production by inhibiting dihydrofolate reductase, providing coverage against gram-positive and gram-negative pathogens. 3

Dosing Regimen

Standard dosing is 1 drop four times daily for 7 days. 2, 5 Peak serum concentrations after instillation are approximately 0.03 mcg/mL trimethoprim and 1 unit/mL polymyxin B. 3

Important Limitations and When NOT to Use Polymyxin B

Gonococcal Conjunctivitis

• Polymyxin B/trimethoprim alone is insufficient for gonococcal conjunctivitis, which requires systemic antibiotic therapy. 1
• Obtain conjunctival cultures and Gram staining before initiating treatment if gonococcal infection is suspected. 1

Chlamydial Conjunctivitis

• Chlamydial conjunctivitis requires systemic antibiotic therapy (oral erythromycin or azithromycin) rather than topical treatment alone. 1

Contact Lens Wearers

• Contact lens wearers are at higher risk for Pseudomonas infection and should receive fluoroquinolones (ofloxacin or ciprofloxacin) rather than polymyxin B/trimethoprim. 1

Moderate to Severe Cases

• For moderate to severe bacterial conjunctivitis with copious purulent discharge, pain, and marked inflammation, fluoroquinolones should be used instead. 1

Follow-Up and Monitoring

• Advise patients to return for follow-up if no improvement is seen after 3-4 days of treatment. 1
• At follow-up, perform interval history, visual acuity measurement, and slit-lamp biomicroscopy. 1

When to Refer to Ophthalmology

Refer to an ophthalmologist for: 1

• Visual loss
• Moderate or severe pain
• Severe purulent discharge
• Corneal involvement
• Conjunctival scarring
• Lack of response to therapy after 3-4 days
• Recurrent episodes

Safety Profile

Polymyxin B/trimethoprim is well tolerated with minimal adverse events. 5, 4 In pediatric studies, patients were very comfortable or moderately comfortable in 89% of cases, with only transient mild-to-moderate adverse events reported. 5