What are the first line antibiotics for an otherwise healthy adult with an uncomplicated ear infection, such as acute otitis media or otitis externa?

First-Line Antibiotics for Ear Infections in Adults

Critical First Step: Distinguish the Type of Ear Infection

The treatment differs completely based on whether you have otitis externa (outer ear canal infection) versus acute otitis media (middle ear infection), and using the wrong approach is the most common error in management. 1

Otitis Externa (Swimmer's Ear)

• Diagnosed by tenderness when pulling the pinna or pressing the tragus, with visible ear canal inflammation 2, 1
• Caused primarily by Pseudomonas aeruginosa (20-60%) and Staphylococcus aureus (10-70%) 2, 3
• Use topical antibiotic drops—NOT oral antibiotics—as first-line therapy 2, 1

Acute Otitis Media (Middle Ear Infection)

• Diagnosed by bulging tympanic membrane, middle ear effusion, and acute onset of ear pain 4, 5
• Caused by Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 4, 5
• Requires oral antibiotics as first-line therapy 4, 1

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Treatment Algorithm for Otitis Externa

First-line: Topical fluoroquinolone drops (ofloxacin or ciprofloxacin-dexamethasone) applied twice daily for 7-10 days. 2, 1, 6

• Topical therapy delivers 100-1000 times higher antibiotic concentrations than oral antibiotics and provides faster pain relief when combined with corticosteroids 1
• Ofloxacin 0.3% otic solution is FDA-approved for otitis externa in adults and covers E. coli, P. aeruginosa, and S. aureus 6
• Avoid oral antibiotics for uncomplicated otitis externa—this is the most common prescribing error and drives antimicrobial resistance 1

When Oral Antibiotics ARE Indicated for Otitis Externa

• Evidence of cellulitis extending beyond the ear canal 3
• Diabetic or immunocompromised patients (concern for necrotizing otitis externa requiring urgent systemic therapy and imaging) 1

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Treatment Algorithm for Acute Otitis Media

First-line: Amoxicillin-clavulanate 500-875 mg twice daily for 5-7 days. 4, 1

• Amoxicillin-clavulanate is preferred over plain amoxicillin in adults because it covers beta-lactamase-producing H. influenzae (17-34% of isolates) and M. catarrhalis (100% produce beta-lactamase) 4, 1
• The standard adult dose is 3 g/day total amoxicillin (in combination with clavulanic acid) 4
• For moderate disease or recent antibiotic exposure within 4-6 weeks, consider high-dose amoxicillin-clavulanate 2000 mg/125 mg twice daily 4
• Treatment duration of 5-7 days is appropriate for uncomplicated cases in adults, with fewer side effects than traditional 10-day courses 4

Alternative for Penicillin Allergy

• Respiratory fluoroquinolones (levofloxacin 500 mg daily or moxifloxacin 400 mg daily) achieve 90-92% clinical efficacy 1, 7
• Second/third-generation cephalosporins (cefdinir, cefuroxime, cefpodoxime) are alternatives if no Type I hypersensitivity to penicillin 4, 1
• Macrolides (azithromycin, clarithromycin) are second-line alternatives but have significantly lower efficacy (77-81% vs 90-92% for fluoroquinolones) 7
• Avoid TMP-SMX due to inconsistent activity against pneumococci and poor benefit/risk ratio 7

Pain Management

• Address pain immediately with oral analgesics (acetaminophen or ibuprofen) regardless of antibiotic decision 4
• NSAIDs at anti-inflammatory doses and corticosteroids have not demonstrated efficacy for AOM treatment 4

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Management of Treatment Failure

Reassess at 48-72 hours if symptoms worsen or fail to improve to confirm diagnosis and exclude other causes. 4, 1

For Otitis Media Treatment Failure

• Switch to a different antibiotic class rather than extending duration 4
• If initial therapy was amoxicillin-clavulanate, consider respiratory fluoroquinolones (levofloxacin, moxifloxacin) or ceftriaxone 50 mg IM for 3 days 4
• Treatment failure is defined as: worsening condition, persistence of symptoms beyond 48 hours after starting antibiotics, or recurrence within 4 days of completing therapy 4

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Critical Pitfalls to Avoid

• Do not prescribe oral antibiotics for uncomplicated otitis externa—this is the most common error 1
• Do not confuse otitis media with effusion (OME) for acute otitis media—isolated middle ear fluid without acute inflammation does not require antibiotics 4
• Isolated redness of the tympanic membrane with normal landmarks is not an indication for antibiotic therapy 4
• Do not miss necrotizing otitis externa in diabetic or immunocompromised patients—this requires urgent systemic antibiotics and imaging 1
• Plain amoxicillin is inadequate for adults with AOM due to high rates of beta-lactamase production (composite susceptibility only 62-89% across all three pathogens) 1