What is the appropriate amoxicillin dosage for a 4‑year‑old child weighing 45 lb (≈20 kg) with acute otitis media and no known penicillin allergy?

Amoxicillin Dosing for Acute Otitis Media in a 4-Year-Old

For a 4-year-old child weighing 45 pounds (20.4 kg) with acute otitis media, prescribe high-dose amoxicillin at 90 mg/kg/day divided into two doses, which equals 1,836 mg total daily (918 mg every 12 hours), administered as approximately 11.5 mL of the 400 mg/5 mL suspension twice daily for 10 days. 1, 2

Rationale for High-Dose Therapy

• High-dose amoxicillin (80–90 mg/kg/day) achieves middle-ear fluid concentrations that exceed the minimum inhibitory concentration for approximately 87% of Streptococcus pneumoniae isolates, including intermediately resistant strains, compared to only 83% coverage with standard dosing (40–45 mg/kg/day). 1, 2

• The high-dose regimen provides adequate antimicrobial coverage against the three principal bacterial pathogens in acute otitis media: Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis. 2, 3

• Children under 6 years of age should receive the full 10-day treatment course to optimize bacterial eradication and prevent recurrence. 1, 2

Practical Dosing Calculation

• Calculate the total daily dose: 20.4 kg × 90 mg/kg = 1,836 mg per day 1, 2

• Divide into two doses: 918 mg every 12 hours 1, 2

• Using 400 mg/5 mL suspension: 918 mg ÷ 80 mg/mL = 11.5 mL per dose 4

• Administer at the start of meals to minimize gastrointestinal intolerance. 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 a 14:1 ratio, divided twice daily) if any of the following apply: 1, 2

• The child received amoxicillin within the previous 30 days 1, 2

• No clinical improvement or worsening after 48–72 hours of amoxicillin monotherapy 1, 2

• Concurrent purulent conjunctivitis (otitis-conjunctivitis syndrome) 1, 2

• Severe presentation at initial visit (high fever, marked otalgia) 2

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

Expected Clinical Response and Monitoring

• Clinical signs (pain, fever, irritability) should begin to improve within 48–72 hours after initiating high-dose amoxicillin. 1, 2, 3

• If no improvement or clinical worsening occurs after 48–72 hours, reassess the diagnosis of acute otitis media and switch to amoxicillin-clavulanate. 1, 2

• If the child fails to improve on amoxicillin-clavulanate, consider ceftriaxone 50 mg/kg administered intramuscularly or intravenously for three days. 2

• Continue treatment for a minimum of 48–72 hours beyond the time the patient becomes asymptomatic. 4

Common Pitfalls to Avoid

• Do not use standard-dose amoxicillin (40–45 mg/kg/day) for acute otitis media, as subtherapeutic doses fail to achieve adequate middle-ear fluid concentrations to overcome resistant organisms and promote antimicrobial resistance. 1

• Verify the suspension concentration (125 mg/5 mL vs 200 mg/5 mL vs 400 mg/5 mL) before calculating the volume to avoid dosing errors. 1

• The 14:1 amoxicillin-clavulanate formulation (90 mg/kg/day amoxicillin + 6.4 mg/kg/day clavulanate) causes significantly less diarrhea than older 7:1 formulations while preserving efficacy against β-lactamase-producing organisms. 1, 2

• Shake the oral suspension well before each use and discard any unused portion after 14 days; refrigeration is preferable but not required. 4