Neomycin-Polymyxin B Otic Dosing and Duration
For acute otitis externa, administer 3-4 drops of neomycin-polymyxin B otic solution 3-4 times daily for 7-10 days maximum, with treatment limited to 10 consecutive days. 1, 2
Specific Dosing by Age
- Adults: Instill 4 drops into the affected ear 3-4 times daily 1, 2
- Children and infants: Instill 3 drops into the affected ear 3-4 times daily (due to smaller ear canal capacity) 1, 2
Administration Technique
Proper instillation is critical for treatment success:
- Have the patient lie with the affected ear upward 1, 2
- Instill drops along the side of the ear canal until filled 3
- Maintain this position for 5 minutes to facilitate penetration 1, 2
- Perform gentle to-and-fro movement of the pinna to eliminate trapped air, or use tragal pumping 3
- The external auditory canal should be thoroughly cleansed and dried with a sterile cotton applicator before administration 1, 2
Alternative wick method:
- Insert a cotton wick into the canal and saturate with solution 1, 2
- Keep wick moist by adding solution every 4 hours 1, 2
- Replace wick at least once every 24 hours 1, 2
Treatment Duration and Expected Response
- Maximum duration: 10 consecutive days 1, 2
- Expected improvement: Within 48-72 hours of initiating therapy 3
- Complete resolution: Most patients have minimal or no symptoms by 7 days 4
Critical Contraindications and Warnings
Do not use neomycin-polymyxin B in patients with:
- Non-intact tympanic membranes (perforation or tympanostomy tubes) due to ototoxicity risk 3
- Known hypersensitivity to neomycin (occurs in 13-30% of patients with chronic otitis externa) 3
When to Consider Treatment Failure
If no improvement occurs within 48-72 hours, consider:
- Inadequate drug delivery (debris blocking canal - perform aural toilet) 3
- Allergic contact dermatitis to neomycin (5-15% of patients with chronic external otitis develop reactions) 4
- Fungal co-infection requiring antifungal therapy 3
- Misdiagnosis or alternative etiology 3
Important Clinical Context
While neomycin-polymyxin B is effective, quinolone-containing drops may be superior:
- Quinolones demonstrate 8% higher bacteriologic cure rates (87% vs 95%) 4
- Declining susceptibility to neomycin and polymyxin B has been documented, with mean MICs increasing above breakpoint for polymyxin B (≥4 μg/mL) in recent studies 5
- Clinical cure rates for neomycin-polymyxin B-hydrocortisone (87%) are lower than ofloxacin (93%) 5
- Neomycin-polymyxin B should be avoided in patients with non-intact tympanic membranes, whereas quinolones are safe in this setting 3
Common pitfall: Neomycin is the most common cause of contact dermatitis from otic preparations, presenting as maculopapular or eczematous eruption on the conchal bowl and ear canal 4. If this occurs, discontinue immediately and apply topical steroid 4.