What is the antibiotic of choice for an otherwise healthy adult with an uncomplicated ear infection?

Antibiotic of Choice for Adult Ear Infections

For uncomplicated otitis externa (swimmer's ear) in adults, topical antibiotic drops—specifically ofloxacin or ciprofloxacin-dexamethasone—are the treatment of choice, NOT oral antibiotics. 1, 2

Distinguishing the Type of Ear Infection

The first critical step is determining whether the infection is otitis externa (outer ear canal infection) or acute otitis media (middle ear infection), as treatment differs fundamentally:

Otitis Externa (Most Common in Adults)

• Lifetime incidence of ~10% in adults 1, 2
• Clinical diagnosis: Tragus or pinna tenderness (often intense and disproportionate to visual findings), ear canal inflammation, pain with manipulation 1
• Pathogens: Pseudomonas aeruginosa (20-60%) and Staphylococcus aureus (10-70%) 1

Acute Otitis Media (Less Common in Adults)

• Clinical diagnosis: Sudden onset fever, otalgia, otorrhea; bulging/reddened tympanic membrane on otoscopy 1, 3
• Pathogens: Streptococcus pneumoniae, Haemophilus influenzae, Moraxella catarrhalis 1, 2, 3

Treatment Algorithm for Otitis Externa

First-Line: Topical Antibiotics

Use topical antibiotic drops with or without corticosteroids for all uncomplicated cases 1, 2:

• Ofloxacin drops OR ciprofloxacin-dexamethasone drops 1, 2
• Apply 2 times daily for up to 10 days 1
• Topical therapy delivers 100-1000 times higher antibiotic concentration than oral antibiotics 2
• Combination antibiotic-corticosteroid drops provide faster pain relief 2

When to Avoid Oral Antibiotics

Do NOT prescribe oral antibiotics for uncomplicated otitis externa 1, 2:

• Oral antibiotics are typically inactive against P. aeruginosa and S. aureus 1
• They promote antibiotic resistance without clinical benefit 1, 2
• 20-40% of patients inappropriately receive oral antibiotics despite lack of efficacy 1

When Systemic Antibiotics ARE Indicated

Reserve oral/IV antibiotics only for 2:

• Extension of infection beyond the ear canal 2
• Diabetes or immunocompromised patients (risk of necrotizing otitis externa) 1, 2
• Prior radiotherapy 2

Expected Response

• Symptoms should improve within 48-72 hours of topical therapy 2
• If no improvement, reassess for complications (necrotizing otitis externa, skull base osteomyelitis) or consider fungal infection 1, 2

Treatment Algorithm for Acute Otitis Media

If acute otitis media is confirmed (less common in adults but requires different treatment):

First-Line: Amoxicillin-Clavulanate

Amoxicillin-clavulanate is the antibiotic of choice for acute otitis media in adults 2, 4:

• Standard dose: 500-875 mg twice daily (1.75 g amoxicillin/250 mg clavulanate per day) 1, 2
• High-dose: 4 g amoxicillin/250 mg clavulanate per day for recent antibiotic exposure or moderate disease 2
• Covers penicillin-intermediate S. pneumoniae, β-lactamase-producing H. influenzae and M. catarrhalis 1, 2
• Predicted clinical efficacy: 90-92% 2

Penicillin Allergy Alternatives

For true penicillin allergy 2, 5:

• Respiratory fluoroquinolones (levofloxacin 500 mg daily OR moxifloxacin 400 mg daily): 90-92% efficacy 1, 2
• Second/third-generation cephalosporins (cefdinir, cefuroxime, cefpodoxime): Safe due to distinct chemical structures; cross-reactivity only ~0.1% 5
• Avoid azithromycin as first-line: Only 77-81% efficacy with 20-25% bacteriologic failure rates 2

Monitoring and Treatment Failure

• Reassess at 48-72 hours if no improvement 2, 3
• Switch to different antibiotic class (not higher dose of same drug) if treatment fails 2
• Provide systemic analgesics (acetaminophen or ibuprofen) for all patients 2

Critical Pitfalls to Avoid

• Never use oral antibiotics for uncomplicated otitis externa—this is the most common error and drives resistance 1, 2
• Do not miss necrotizing otitis externa in diabetic/immunocompromised patients—requires urgent systemic antibiotics and imaging 1, 2
• Do not continue same antibiotic beyond 72 hours without improvement—reassess diagnosis and change therapy 2
• Do not avoid all cephalosporins in penicillin allergy—modern second/third-generation agents are safe 5
• Consider fungal infection (Aspergillus, Candida) when standard bacterial treatment fails 1