What is the appropriate amoxicillin dose for a 22.23 kg child with uncomplicated Group A Streptococcus pharyngitis?

Amoxicillin Dosing for a 22.23 kg Child with Group A Streptococcal Pharyngitis

For this 22.23 kg child with uncomplicated strep throat, prescribe amoxicillin 500 mg twice daily (or 750 mg once daily) for 10 days. 1, 2

Weight-Based Dosing Calculation

• This child weighs less than 40 kg, so pediatric weight-based dosing applies rather than adult dosing 1, 2
• The recommended dose is 25 mg/kg/day divided twice daily for mild-to-moderate infections, which equals approximately 556 mg/day total, or 278 mg per dose 3
• In practice, round to 500 mg twice daily (22.5 mg/kg per dose), which is the standard commercially available suspension strength and falls within the recommended range 2, 3
• An alternative once-daily regimen of 750 mg once daily (approximately 34 mg/kg/day) is equally effective and may improve adherence 1, 4, 5

Dosing Options for This Patient

• Option 1 (Preferred for twice-daily): Amoxicillin 500 mg (or 10 mL of 250 mg/5 mL suspension) every 12 hours for 10 days 2, 3
• Option 2 (Once-daily alternative): Amoxicillin 750 mg (or 15 mL of 250 mg/5 mL suspension) once daily for 10 days 1, 4
• Option 3 (Three times daily): Amoxicillin 250 mg every 8 hours for 10 days, though this is less convenient 6

Critical Treatment Principles

• The 10-day duration is non-negotiable to prevent acute rheumatic fever, regardless of when symptoms resolve 1, 2, 3
• Treatment should be taken at the start of meals to minimize gastrointestinal intolerance 3
• The once-daily regimen has been proven non-inferior to twice-daily dosing in multiple studies, with bacteriologic cure rates of 79-87% 4, 5, 7

Common Pitfalls to Avoid

• Do not use the 875 mg tablet in children under 40 kg, as this exceeds recommended pediatric dosing 1
• Do not prescribe shorter courses (e.g., 5 days) despite some retrospective data suggesting efficacy, as guidelines do not endorse this for routine therapy to prevent rheumatic fever 1, 8
• Do not stop antibiotics early even if the child feels better after 3-4 days, as this increases the risk of rheumatic fever 1, 2
• Do not underdose at 20 mg/kg/day when 25 mg/kg/day twice daily is recommended for adequate eradication 2, 7

Why Amoxicillin Over Penicillin V

• Amoxicillin is equally effective to penicillin V but offers superior palatability in suspension form, improving adherence in young children 6, 1
• Studies demonstrate amoxicillin at 40 mg/kg/day achieves significantly higher bacteriologic cure rates (79.3%) compared to standard-dose penicillin V (54.5%) 7

Penicillin Allergy Alternatives

• For non-anaphylactic penicillin allergy: Cephalexin 20 mg/kg twice daily (maximum 500 mg per dose) for 10 days 2
• For immediate-type hypersensitivity: Clindamycin 7 mg/kg three times daily (maximum 300 mg per dose) or azithromycin 12 mg/kg once daily for 5 days 2
• Do not use first-generation cephalosporins in patients with immediate-type hypersensitivity to β-lactams 6

Monitoring and Follow-Up

• Symptoms typically resolve within 3-4 days, but this does not indicate treatment completion 1
• Routine post-treatment testing is not recommended unless the child has specific risk factors for rheumatic fever 2
• If symptoms persist beyond 72 hours, consider treatment failure and evaluate for complications or alternative diagnoses 9