Amoxicillin Dosing for Adult Ear Infections
For adults with acute otitis media, amoxicillin should be prescribed at 500 mg three times daily (1500 mg/day total) for standard cases, or high-dose amoxicillin at 4000 mg/day divided into 2-3 doses for patients with risk factors such as recent antibiotic exposure or in areas with high rates of resistant Streptococcus pneumoniae. 1
Standard Dosing Regimen
The FDA-approved adult dosing range for amoxicillin in upper respiratory tract infections of the ear is 750 to 1750 mg/day in divided doses every 8 to 12 hours. 2
For routine acute otitis media in adults without recent antibiotic use, prescribe amoxicillin 500 mg three times daily (every 8 hours) for 5-10 days. 1, 2
This standard dose provides adequate coverage for most common pathogens including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. 1
High-Dose Therapy for Resistant Organisms
High-dose amoxicillin (4000 mg/day) is specifically indicated for adults at high risk of infection with resistant bacteria. 1
When to use high-dose therapy:
- Patients who received antibiotics within the previous 4-6 weeks 3, 1
- Geographic areas with high rates of penicillin-nonsusceptible S. pneumoniae (>25% resistance) 1
- Treatment failures with standard-dose therapy 1
Rationale for high-dose therapy:
High-dose amoxicillin achieves middle ear fluid concentrations exceeding the minimum inhibitory concentration (MIC) for intermediately resistant S. pneumoniae (penicillin MIC 0.12-1.0 μg/mL) and many highly resistant serotypes (penicillin MIC ≥2 μg/mL). 3, 1
Approximately 83-87% of S. pneumoniae isolates are susceptible to high-dose amoxicillin, compared to lower susceptibility rates with standard dosing. 3
Serum levels of amoxicillin increase linearly with dose, and gastrointestinal absorption is not a limiting factor, making higher doses both feasible and well-tolerated. 3
When to Use Amoxicillin-Clavulanate Instead
Switch to amoxicillin-clavulanate (4000 mg amoxicillin/250 mg clavulanate per day) rather than amoxicillin alone in the following situations: 1
- Recent antibiotic exposure (within 30 days) 3, 1
- Concurrent purulent conjunctivitis 3, 1
- Treatment failure after 48-72 hours of amoxicillin monotherapy 1
Why clavulanate matters:
Approximately 48-58% of H. influenzae and 90-100% of M. catarrhalis produce β-lactamase enzymes that inactivate amoxicillin. 3, 1
The clavulanate component inhibits β-lactamase, preserving amoxicillin activity against these resistant organisms. 3, 1
In treatment failures, β-lactamase-producing organisms are the predominant pathogens isolated. 4
Treatment Duration and Monitoring
Standard treatment duration is 5-10 days. 1
Mandatory reassessment at 48-72 hours is required if no clinical improvement occurs. 1
If symptoms worsen or fail to improve after 72 hours, switch to amoxicillin-clavulanate or an alternative agent. 1
Alternatives for Penicillin Allergy
For patients with non-type I (non-anaphylactic) penicillin allergy: 1
- Cefdinir 300 mg twice daily or 600 mg once daily 1
- Cefuroxime axetil 500 mg twice daily 1
- Cefpodoxime proxetil 3, 1
For patients with type I hypersensitivity (anaphylaxis, Stevens-Johnson syndrome): 2
- Avoid all β-lactams including cephalosporins 2
- Consider respiratory fluoroquinolones (levofloxacin 750 mg daily, moxifloxacin 400 mg daily) or macrolides (azithromycin, clarithromycin), though bacteriologic failure rates of 20-25% are possible with macrolides 3
Common Pitfalls to Avoid
Do not underdose in heavier patients: While the standard 500 mg three times daily is appropriate for most adults, high-risk patients require the full 4000 mg/day to achieve therapeutic middle ear fluid concentrations. 1
Do not use first-generation cephalosporins (e.g., cephalexin): These agents have poor coverage for H. influenzae and are inappropriate for otitis media. 1
Do not continue ineffective therapy beyond 72 hours: Early recognition of treatment failure and prompt switching to amoxicillin-clavulanate or alternative agents prevents complications such as mastoiditis. 1
Do not prescribe twice-daily dosing for high-dose therapy without ensuring adequate total daily dose: The 4000 mg/day high-dose regimen can be divided into 2000 mg twice daily or approximately 1333 mg three times daily. 1, 2