What is the appropriate amoxicillin dose for acute otitis media in a 7‑year‑old child weighing 21.68 kg?

Amoxicillin Dosing for Acute Otitis Media in a 7-Year-Old Weighing 21.68 kg

Administer high-dose amoxicillin 1,950 mg per day (975 mg twice daily) for 10 days, calculated as 90 mg/kg/day divided into 2 doses. 1

Weight-Based Calculation

• For this 21.68 kg child, the calculation is: 90 mg/kg/day × 21.68 kg = 1,951 mg/day, rounded to 1,950 mg total daily dose (975 mg every 12 hours). 1
• The maximum single dose is 2,000 mg regardless of weight, so this dose is well within safe limits. 2

Rationale for High-Dose Therapy

• High-dose amoxicillin (80–90 mg/kg/day) is the recommended first-line treatment for acute otitis media because it achieves middle ear fluid concentrations that exceed the minimum inhibitory concentration for intermediately resistant Streptococcus pneumoniae (penicillin MIC 0.12–1.0 μg/mL) and many highly resistant serotypes (penicillin MIC ≥2 μg/mL). 1
• This dosing provides superior bacteriologic and clinical efficacy compared to standard-dose amoxicillin (40–45 mg/kg/day), with approximately 87% susceptibility of S. pneumoniae isolates to high-dose therapy versus 83% to standard-dose. 1
• High-dose amoxicillin eradicates 92% of S. pneumoniae from middle ear fluid by days 4–6 of therapy, including penicillin-nonsusceptible strains. 3

Treatment Duration

• Continue therapy for 10 days in children under 6 years of age with acute otitis media. 2
• Clinical improvement (reduced pain, fever, irritability) should be evident within 48–72 hours of starting treatment. 4

When to Switch to Amoxicillin-Clavulanate

Switch to high-dose amoxicillin-clavulanate (90 mg/kg/day amoxicillin + 6.4 mg/kg/day clavulanate in 2 divided doses) if any of the following apply:

• The child received amoxicillin in the previous 30 days. 1
• No clinical improvement or worsening after 48–72 hours on amoxicillin alone. 1
• Concurrent purulent conjunctivitis (otitis-conjunctivitis syndrome). 1
• Severe presentation at onset (high fever ≥39°C, marked otalgia, bilateral disease in a child under 2 years). 4

The rationale for switching is that β-lactamase-producing Haemophilus influenzae (present in 58–82% of isolates) and Moraxella catarrhalis are resistant to amoxicillin alone but susceptible to amoxicillin-clavulanate. 1, 3

Practical Administration

• Amoxicillin suspension is typically available as 400 mg/5 mL; for 975 mg per dose, administer 12.2 mL (approximately 12 mL) twice daily. 2
• Administer doses every 12 hours to maintain therapeutic middle ear fluid concentrations throughout the dosing interval. 1
• The twice-daily regimen has significantly lower rates of diarrhea (14%) compared to three-times-daily dosing (34%), with severe diarrhea or withdrawal rates of only 3% versus 8%. 5

Common Pitfalls to Avoid

• Do not use standard-dose amoxicillin (40–45 mg/kg/day) for acute otitis media, as it fails to achieve adequate concentrations against resistant S. pneumoniae and leads to treatment failure rates of 20–25% when risk factors for resistant organisms are present. 4
• Do not underdose based on age-based algorithms rather than weight-based calculations; this child requires the full 90 mg/kg/day, not a fixed pediatric dose. 2
• Reassess at 48–72 hours if symptoms persist or worsen; failure to do so may result in complications from inadequately treated bacterial infection. 4
• Verify suspension concentration before dispensing (e.g., 200 mg/5 mL versus 400 mg/5 mL) to avoid dosing errors. 2

Expected Outcomes

• Clinical cure rates at end of therapy (days 12–14) are approximately 87% with high-dose amoxicillin. 5
• Bacteriologic eradication of S. pneumoniae occurs in 92% of cases, including penicillin-resistant strains with MIC ≤2 μg/mL. 3
• The high-dose regimen demonstrates 90–92% predicted clinical efficacy against the principal AOM pathogens (S. pneumoniae, H. influenzae, M. catarrhalis). 4