Polymyxin B Ophthalmic Solution Dosing for Conjunctivitis
For bacterial conjunctivitis, administer polymyxin B 0.1% (10,000 IU/mL) ophthalmic solution as 1-2 drops in the affected eye(s) four times daily for 5-7 days in both adults and neonates. 1
Standard Dosing Regimen
- Adults and children: Instill 1-2 drops of polymyxin B/trimethoprim ophthalmic solution four times daily for 7 days 2, 3, 4
- Neonates (≤28 days): The same dosing regimen applies, though systemic therapy is required for gonococcal or chlamydial conjunctivitis rather than topical treatment alone 1, 5
Clinical Efficacy and Treatment Response
- Clinical improvement should be evident within 24-48 hours, with complete resolution of signs and symptoms in approximately 44% of patients by 48 hours when using polymyxin B/trimethoprim 2
- By 7-10 days post-treatment, clinical cure rates reach 95-96% for polymyxin B/trimethoprim, which is non-inferior to fluoroquinolones 6
- Bacteriologic cure rates range from 68-83% at 2-7 days after completion of therapy 4
Important Clinical Considerations
Polymyxin B/trimethoprim is insufficient as monotherapy for:
- Gonococcal conjunctivitis: Requires systemic ceftriaxone (250 mg IM single dose for adults; 25-50 mg/kg IV/IM for neonates, max 125 mg) plus azithromycin 1 g orally 1, 5
- Chlamydial conjunctivitis: Requires systemic azithromycin 1 g orally single dose or doxycycline 100 mg twice daily for 7 days 1, 5
- MRSA conjunctivitis: May require compounded topical vancomycin, as MRSA is resistant to polymyxin B 1
When to Escalate or Modify Treatment
- Return for follow-up if no improvement after 3-4 days of treatment, at which point interval history, visual acuity measurement, and slit-lamp biomicroscopy should be performed 1
- Immediate ophthalmology referral is warranted for visual loss, moderate-to-severe pain, severe purulent discharge, corneal involvement, conjunctival scarring, lack of response to therapy, or recurrent episodes 1
- Consider switching to fluoroquinolones if no improvement by 48 hours or if the patient is a contact lens wearer at higher risk for Pseudomonas infection 1, 2
Cost-Effectiveness Considerations
- Polymyxin B/trimethoprim is significantly less expensive than fluoroquinolones while maintaining equivalent clinical cure rates for uncomplicated bacterial conjunctivitis 6
- For mild cases in immunocompetent patients without contact lens use, polymyxin B/trimethoprim represents a cost-effective first-line option 1
- However, moxifloxacin achieves faster symptom resolution (81% complete resolution at 48 hours vs. 44% for polymyxin B/trimethoprim), which may justify its use when rapid return to work/school is prioritized 2
Administration Technique
- Remove contact lenses before instillation and do not re-insert until infection has completely resolved 5
- Avoid contaminating the dropper tip by not touching it to the eye or any surface 1
- Counsel patients on strict hand hygiene, avoiding eye rubbing, using separate towels, and avoiding close contact during the contagious period 1