Amoxicillin Dosing for Ear Infection in a 5-Year-Old Weighing 50 lb
For a 5-year-old child weighing 50 pounds (22.7 kg) with an ear infection, prescribe high-dose amoxicillin at 80-90 mg/kg/day divided into two doses daily, which equals approximately 900-1000 mg twice daily (or practically, 1000 mg twice daily) for 10 days. 1, 2
Dose Calculation
- Weight conversion: 50 lb = 22.7 kg 2
- Recommended dosing: 80-90 mg/kg/day in 2 divided doses 1, 2
- Total daily dose: 1816-2043 mg/day 2
- Practical prescription: 1000 mg (or 900 mg if available) twice daily, which provides approximately 88 mg/kg/day 2
Rationale for High-Dose Amoxicillin
High-dose amoxicillin is the first-line treatment for acute otitis media because it provides effective coverage against drug-resistant Streptococcus pneumoniae while maintaining excellent safety, low cost, acceptable taste, and narrow microbiologic spectrum. 1, 2
- High-dose amoxicillin achieves middle ear fluid levels that exceed the minimum inhibitory concentration (MIC) for intermediately resistant S. pneumoniae (penicillin MICs 0.12-1.0 μg/mL) and many highly resistant strains (penicillin MICs ≥2 μg/mL) 1
- Approximately 87% of S. pneumoniae isolates are susceptible to high-dose amoxicillin 1
- Standard-dose amoxicillin (40-45 mg/kg/day) is inadequate for resistant strains, particularly during viral coinfection 3
Treatment Duration
- Standard duration: 10 days for children under 6 years of age 1, 4
- Shorter duration: 5-7 days may be considered for children over 2 years with uncomplicated, mild disease 2
- For this 5-year-old, 10 days is the safest recommendation to ensure adequate bacterial eradication 1, 4
When to Switch Antibiotics
Switch to high-dose amoxicillin-clavulanate (90 mg/kg/day of amoxicillin with 6.4 mg/kg/day of clavulanate in 2 divided doses) if: 1, 2
- The child received amoxicillin in the previous 30 days 1
- Concurrent purulent conjunctivitis is present (otitis-conjunctivitis syndrome) 1
- No clinical improvement after 48-72 hours of amoxicillin therapy 1, 2
- Coverage for β-lactamase-producing Haemophilus influenzae or Moraxella catarrhalis is needed 1
Clinical Reassessment
Reassess the patient at 48-72 hours if symptoms fail to improve. 1, 2
- Treatment failure is defined as worsening condition, persistence of symptoms beyond 48 hours, or no improvement by 72 hours 2
- β-lactamase-producing H. influenzae is the most common cause of amoxicillin treatment failure, accounting for 64% of bacteriologic failures 5
- If treatment fails, switch to amoxicillin-clavulanate or consider ceftriaxone (50 mg/kg IM/IV daily for 3 days) 1
Pain Management
Address pain management concurrently with antibiotic therapy during the first 24 hours. 1, 2
- Pain relief should be provided regardless of whether antibiotics are prescribed 1
- Options include acetaminophen or ibuprofen at weight-appropriate doses 1
Common Pitfalls to Avoid
- Do not prescribe standard-dose amoxicillin (40 mg/kg/day): This is inadequate for drug-resistant S. pneumoniae and results in higher failure rates 1, 3, 5
- Do not underdose: Ensure the total daily dose reaches 80-90 mg/kg/day, not just 40-50 mg/kg/day 1, 2
- Do not use macrolides (azithromycin, clarithromycin) as first-line therapy: These have inferior efficacy against S. pneumoniae compared to high-dose amoxicillin 1
- Administer at the start of meals: This minimizes gastrointestinal intolerance 4
Penicillin Allergy Considerations
If the child has a non-severe penicillin allergy (e.g., rash without anaphylaxis): 1
- Cefdinir (14 mg/kg/day in 1-2 doses) is preferred 1
- Cefuroxime (30 mg/kg/day in 2 doses) or cefpodoxime (10 mg/kg/day in 2 doses) are alternatives 1
- Cross-reactivity between penicillins and cephalosporins is lower than historically reported (likely <10%) 1
If the child has a history of immediate Type I hypersensitivity (anaphylaxis) to β-lactams: 1