What is the recommended dosage of amoxicillin (amoxicillin) for a 12-year-old child weighing 75 pounds (approximately 34 kilograms) with an ear infection?

Amoxicillin Dosage for 12-Year-Old with Ear Infection (75 lbs/34 kg)

For a 12-year-old child weighing 34 kg with acute otitis media, prescribe high-dose amoxicillin at 80-90 mg/kg/day divided into two doses, which equals 1360-1530 mg twice daily (2720-3060 mg total daily dose). 1, 2

Dosage Calculation

• The American Academy of Pediatrics recommends 80-90 mg/kg/day of amoxicillin as first-line treatment for acute otitis media, divided into two daily doses 1, 2
• For this 34 kg child: 80-90 mg/kg/day × 34 kg = 2720-3060 mg/day total 2
• Divided into 2 doses = 1360-1530 mg per dose, given twice daily 1, 2
• The FDA label confirms dosing for severe ear/nose/throat infections at 45 mg/kg/day in divided doses every 12 hours, which aligns with this recommendation 3

Rationale for High-Dose Therapy

• High-dose amoxicillin (80-90 mg/kg/day) achieves middle ear fluid levels that exceed the minimum inhibitory concentration (MIC) for intermediately resistant Streptococcus pneumoniae (penicillin MICs 0.12-1.0 μg/mL) and many highly resistant serotypes (penicillin MICs ≥2 μg/mL) 1
• This dosing has demonstrated superior bacteriologic and clinical efficacy compared to standard 40 mg/kg/day regimens, with eradication rates of 92% for S. pneumoniae 1, 4
• Standard-dose amoxicillin (40 mg/kg/day) is inadequate to effectively eradicate resistant S. pneumoniae, particularly during viral coinfection 5

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 in a 14:1 ratio) if: 1, 6, 2

• The child has taken amoxicillin in the previous 30 days 1, 6
• Concurrent purulent conjunctivitis is present 1, 6
• The child attends daycare 6
• Coverage for β-lactamase-producing H. influenzae and M. catarrhalis is needed 1

Treatment Duration and Monitoring

• Continue treatment for minimum 10 days for acute otitis media 1, 3
• Clinical improvement should occur within 24-48 hours of starting therapy 6
• If no improvement within 48-72 hours, reassess the diagnosis and consider changing to amoxicillin-clavulanate 6
• The predominant pathogens in amoxicillin treatment failures are β-lactamase-producing organisms, particularly H. influenzae 4

Administration Instructions

• Administer at the start of meals to minimize gastrointestinal intolerance 3
• Twice-daily dosing (every 12 hours) is as effective as three-times-daily dosing and improves compliance 7
• For oral suspension, shake well before each use and refrigerate (though not required); discard unused portion after 14 days 3

Common Pitfalls to Avoid

• Underdosing is the most common prescribing error—ensure accurate weight-based calculations rather than using age-based estimates 2
• Do not prescribe the 875 mg tablet formulation for twice-daily dosing in this patient, as it would provide only 1750 mg/day (51 mg/kg/day), which is below the recommended 80-90 mg/kg/day 3
• Failure to complete the full 10-day course may lead to treatment failure and bacterial resistance 2
• Not recognizing indications for amoxicillin-clavulanate (recent amoxicillin use, concurrent conjunctivitis) leads to preventable treatment failures 1, 6