What is the proper dosing schedule, administration technique, and precautions for polymyxin B ophthalmic drops in treating confirmed bacterial conjunctivitis (pink eye) in a patient without a polymyxin allergy?

Polymyxin B Ophthalmic Drops for Bacterial Conjunctivitis

For confirmed bacterial conjunctivitis without polymyxin allergy, instill 1-2 drops of polymyxin B/trimethoprim four times daily for 5-7 days, though moxifloxacin is significantly more effective and should be preferred when available. 1, 2

Dosing Schedule

• Standard regimen: 1-2 drops in the affected eye(s) four times daily for 5-7 days 1, 3
• Continue the full course even if symptoms improve earlier to prevent recurrence and resistance 3
• No tapering is required; simply discontinue after completing the 5-7 day course 3

Administration Technique

• Wash hands thoroughly with soap and water before and after instillation 1
• Tilt head back and pull down the lower eyelid to create a small pocket 1
• Instill 1-2 drops into the conjunctival sac, avoiding contact between the dropper tip and the eye or eyelid 1
• Close the eye gently for 1-2 minutes without blinking excessively 1
• Wipe away excess medication with a clean tissue 1
• Discard the bottle after completing treatment to avoid contamination and cross-infection 1

Expected Clinical Response

• You should see reduced discharge, decreased redness, and lessened eyelid swelling within 48-72 hours 3
• Return for re-evaluation if no improvement occurs after 3-4 days, as this may indicate resistant organisms (particularly MRSA), viral etiology, or gonococcal/chlamydial infection requiring systemic antibiotics 1, 3

Critical Red Flags Requiring Immediate Ophthalmology Referral

Do not use polymyxin drops and arrange urgent ophthalmology evaluation if any of the following are present:

• Visual loss or significant change in vision 1
• Moderate to severe eye pain (beyond mild irritation) 1
• Corneal involvement such as opacity, infiltrate, or ulcer 1
• Severe purulent discharge suggesting possible gonococcal infection 1, 3
• History of herpes simplex virus eye disease 1
• Immunocompromised state 1
• Conjunctival scarring or lack of response to therapy 1

Important Clinical Considerations

Polymyxin/Trimethoprim vs. Fluoroquinolones

While polymyxin B/trimethoprim is effective for routine bacterial conjunctivitis, moxifloxacin 0.5% three times daily achieves complete resolution in 81% of patients by 48 hours compared to only 44% with polymyxin/trimethoprim (P = 0.001) 2. The American Academy of Ophthalmology recommends fluoroquinolones as first-line therapy due to superior gram-positive coverage, including activity against some MRSA strains 1, 3.

Infections Requiring Systemic Antibiotics

Polymyxin/trimethoprim alone is insufficient for:

• Gonococcal conjunctivitis: Requires ceftriaxone 250 mg IM single dose plus azithromycin 1 g orally single dose, with daily monitoring until resolution 1, 3
• Chlamydial conjunctivitis: Requires azithromycin 1 g orally single dose or doxycycline 100 mg orally twice daily for 7 days 1, 3
• Both conditions require evaluation for concurrent genital infections and treatment of sexual partners; consider sexual abuse in children 1, 3

MRSA Considerations

If the patient fails to respond to polymyxin/trimethoprim within 48-72 hours and MRSA is suspected (particularly in nursing home residents or those with recent healthcare exposure), compounded topical vancomycin may be required, as MRSA isolates are generally resistant to polymyxin and other commercially available topical antibiotics 1, 3.

Infection Control Measures

• Practice strict hand hygiene with soap and water 1
• Avoid sharing towels, pillowcases, or eye makeup 1
• Avoid close contact for at least 24 hours after starting treatment 1
• Do not wear contact lenses during treatment and for 24 hours after completing therapy 1
• Children may return to school 24 hours after starting treatment if symptoms are improving 4

Common Pitfalls to Avoid

• Do not use topical corticosteroids (such as Tobradex) without definitively ruling out HSV conjunctivitis, as steroids potentiate viral replication and can cause corneal perforation 1
• Do not prescribe oral antibiotics for routine bacterial conjunctivitis, as topical therapy achieves superior tissue concentrations; oral antibiotics are reserved exclusively for gonococcal and chlamydial infections 1, 3
• Do not use polymyxin drops for viral conjunctivitis, which requires only supportive care with artificial tears and cold compresses 1
• Bacterial conjunctivitis is often self-limited in immunocompetent adults, resolving spontaneously in 64% of cases by days 6-10, but topical antibiotics accelerate resolution and reduce transmissibility 1, 3