Amoxicillin Dosing for a 100-Pound Child with Ear Infection
For a 100-pound (45 kg) child with an ear infection, administer high-dose amoxicillin at 80-90 mg/kg/day divided into 2 doses, which equals approximately 1800-2000 mg per day (900-1000 mg twice daily), with a maximum of 2 grams per dose. 1, 2
Weight Conversion and Dose Calculation
- A 100-pound child weighs approximately 45 kg 3
- At 80-90 mg/kg/day: this equals 3600-4050 mg/day total 1, 2
- However, the maximum single dose is 2 grams, so the practical dosing is 2000 mg (2 grams) twice daily 4, 3
- This can be given as either 875 mg tablets (2 tablets twice daily = 1750 mg twice daily) or 1000 mg twice daily if available formulations allow 3
Rationale for High-Dose Therapy
High-dose amoxicillin is the American Academy of Pediatrics' first-line recommendation for acute otitis media because it achieves middle ear fluid concentrations that overcome resistance in Streptococcus pneumoniae, the most common bacterial pathogen. 1, 2
- High-dose therapy (80-90 mg/kg/day) achieves middle ear fluid levels exceeding the minimum inhibitory concentration for intermediately resistant S. pneumoniae for longer periods during the dosing interval 1, 2
- Approximately 87% of S. pneumoniae isolates are susceptible to high-dose amoxicillin compared to only 83% with standard dosing 2
- This dosing is effective, safe, has acceptable taste, low cost, and a relatively narrow microbiologic spectrum 4, 1
Administration Instructions
- Give amoxicillin at the start of a meal to minimize gastrointestinal intolerance 3
- Divide the total daily dose into 2 equal doses given every 12 hours 1, 2, 3
- Continue treatment for 10 days 2
When to Switch to Amoxicillin-Clavulanate
Consider switching to high-dose amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate) if: 1, 2
- The child received amoxicillin within the previous 30 days 1, 2
- Concurrent purulent conjunctivitis is present 1, 2
- No clinical improvement occurs after 48-72 hours on amoxicillin 1, 2
- Coverage for β-lactamase-producing Haemophilus influenzae or Moraxella catarrhalis is specifically desired 1, 2
Treatment Failure Management
- Reassess if no improvement occurs within 48-72 hours 2
- Switch to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin with 6.4 mg/kg/day clavulanate in 2 divided doses) 1
- Alternatively, ceftriaxone 50 mg/kg IM or IV can be used for treatment failures 1
- The 14:1 ratio formulation of amoxicillin to clavulanate causes less diarrhea than other ratios 2
Important Clinical Caveats
- For children attending daycare, younger than 2 years, or recently treated with antimicrobials, consider starting with high-dose amoxicillin-clavulanate rather than amoxicillin alone 4
- Beta-lactamase-producing H. influenzae (present in 34% of cases in one study) are the predominant pathogens in amoxicillin treatment failures 5
- Viral coinfection may reduce amoxicillin middle ear fluid penetration and decrease treatment efficacy 6
- Address pain management regardless of antibiotic choice 2