What if Polytrim (polymyxin B and trimethoprim) is not effective in treating bacterial conjunctivitis?

What to Do When Polytrim (Polymyxin B/Trimethoprim) Fails

If Polytrim is not effective after 3-4 days, switch to topical moxifloxacin 0.5% three times daily, as it achieves complete resolution in 81% of cases by 48 hours compared to only 44% with Polytrim, and simultaneously evaluate for gonococcal or chlamydial infection which require systemic antibiotics. 1, 2

Immediate Assessment at 3-4 Days

When a patient returns without improvement on Polytrim, perform the following evaluation 1:

• Measure visual acuity - any decrease requires immediate ophthalmology referral 1
• Slit-lamp examination looking specifically for:
  • Corneal involvement (infiltrate, ulcer, opacity) - immediate referral needed 1
  • Severe purulent discharge suggesting gonococcal infection 1
  • Follicular reaction with watery discharge suggesting viral etiology 3
  • Preauricular lymphadenopathy 4

First-Line Switch: Moxifloxacin

Switch to moxifloxacin 0.5% ophthalmic solution, 1 drop three times daily for 5-7 days, as this fourth-generation fluoroquinolone provides superior gram-positive coverage including some MRSA strains and achieves significantly faster cure rates than Polytrim. 1, 2

The evidence strongly supports this switch:

• Moxifloxacin achieved 81% complete resolution at 48 hours versus 44% with Polytrim (P = 0.001) 2
• Superior coverage against S. aureus, S. pneumoniae, and H. influenzae 1, 3
• Microbiological eradication rates of 84-94% 3

Rule Out Special Pathogens Requiring Systemic Therapy

Gonococcal Conjunctivitis

Obtain conjunctival cultures and Gram staining immediately if you see: 1, 3

• Copious purulent discharge
• Marked inflammation and pain
• Severe lid swelling

Treatment requires systemic antibiotics, not just topical therapy: 1, 3

• Adults: Ceftriaxone 1 g IM single dose PLUS azithromycin 1 g orally single dose 1
• Daily monitoring until resolution is mandatory 1, 3
• Critical pitfall: Gonococcal conjunctivitis can cause corneal perforation if untreated 3

Chlamydial Conjunctivitis

Systemic therapy is required because topical antibiotics alone are insufficient: 1, 3

• Adults: Azithromycin 1 g orally single dose OR doxycycline 100 mg twice daily for 7 days 3
• More than 50% of infants have concurrent infection at other sites 3
• Screen for concurrent genital infections and treat sexual partners 3
• Consider sexual abuse in children with gonococcal or chlamydial conjunctivitis 1, 3

Alternative Topical Options If Moxifloxacin Unavailable

If fluoroquinolones are not accessible, the following alternatives are endorsed 1, 3:

• Gentamicin 0.3% four times daily for 5-7 days 1
• Tobramycin 0.3% four times daily for 5-7 days 1
• Ofloxacin 0.3% four times daily for 5-7 days 1

Suspected MRSA Conjunctivitis

If the patient fails moxifloxacin within 48-72 hours, consider MRSA and compounded topical vancomycin, as MRSA isolates are generally resistant to fluoroquinolones and aminoglycosides but susceptible to vancomycin. 1, 3

Risk factors for MRSA include 1:

• Nursing home residence
• Recent hospitalization
• Recent fluoroquinolone use
• Recurrent infections

When to Refer to Ophthalmology Immediately

Refer urgently if any of the following are present: 1, 3

• Visual loss
• Moderate to severe pain
• Corneal involvement (infiltrate, ulcer, opacity)
• Conjunctival scarring
• Severe purulent discharge
• Immunocompromised state
• History of HSV eye disease
• Lack of response after switching antibiotics

Critical Pitfalls to Avoid

Never add topical corticosteroids to failed Polytrim therapy without first ruling out HSV conjunctivitis, as steroids potentiate viral replication and can cause corneal perforation. 1, 3

Do not use oral antibiotics like Augmentin for routine bacterial conjunctivitis, as oral antibiotics cannot reach therapeutic levels in the conjunctiva and are reserved exclusively for gonococcal and chlamydial infections. 3

Avoid continuing subtherapeutic antibiotic dosing, as this increases resistance risk. 1

Why Polytrim May Fail

Historical data shows Polytrim has lower efficacy compared to newer agents 2, 5:

• Only 44% complete resolution at 48 hours versus 81% with moxifloxacin 2
• Requires four-times-daily dosing versus three times daily for moxifloxacin, affecting compliance 2
• Less effective against resistant organisms 1

Infection Control During Treatment Failure

Counsel patients on strict hand hygiene with soap and water, avoiding eye rubbing, using separate towels, and avoiding close contact during the contagious period to prevent transmission. 1, 3