Amoxicillin Dosing for Streptococcal Pharyngitis in a 10-Year-Old Child
For a 10-year-old child weighing 45.5 kg with streptococcal pharyngitis, prescribe amoxicillin 1000 mg once daily OR 500 mg twice daily for 10 days. 1, 2
Weight-Based Dosing Considerations
Since this child weighs greater than 40 kg, they should receive adult dosing rather than pediatric weight-based calculations 2:
- Once-daily regimen: 1000 mg once daily (maximum dose for patients ≥40 kg) 3
- Twice-daily regimen: 500 mg every 12 hours 1, 2
- Alternative: 250 mg three times daily or four times daily 1
The FDA label specifies that for ear/nose/throat infections of mild to moderate severity in patients weighing ≥40 kg, the recommended dose is 500 mg every 12 hours or 250 mg every 8 hours 2. However, the once-daily 1000 mg regimen has been proven non-inferior in a large controlled trial and may improve adherence 3.
Duration of Therapy
All regimens must be continued for a full 10 days to prevent acute rheumatic fever, regardless of symptom resolution 1, 2. This is critical even though symptoms typically resolve within 3-4 days 1.
Why Amoxicillin Over Penicillin V
While penicillin V remains the guideline-recommended first-line agent 1, amoxicillin is explicitly noted as equally effective and is "often used in place of oral penicillin V for young children" due to better palatability 1. For a 10-year-old, either is appropriate, but amoxicillin offers:
- Superior bacteriologic cure rates when dosed at 40-50 mg/kg/day compared to standard penicillin V dosing 4
- Once-daily dosing option that improves adherence 3
- Better taste acceptance in suspension form 1
Administration Instructions
- Take at the start of meals to minimize gastrointestinal intolerance 2
- Shake suspension well before each use if using liquid formulation 2
- Treatment should continue for minimum 48-72 hours beyond symptom resolution 2
Alternative Regimens for Penicillin Allergy
If the patient has a non-anaphylactic penicillin allergy, use first-generation cephalosporins for 10 days 1, 5. For immediate-type hypersensitivity to β-lactams, use erythromycin or clindamycin 1:
- Clindamycin: 40 mg/kg/day divided into 3 doses (approximately 600 mg three times daily for this weight) 1, 6
- Erythromycin: Varies by formulation, typically 20-40 mg/kg/day 1
Note that azithromycin and clarithromycin have significant resistance in some U.S. regions and should be avoided 5.
Common Pitfalls to Avoid
- Do not use adult 875 mg tablets in children <40 kg, as this exceeds recommended pediatric dosing 2
- Do not prescribe shorter courses (e.g., 5 days) despite some studies suggesting efficacy, as guidelines do not endorse this for routine therapy 1
- Do not stop antibiotics early even if the child feels better, as this increases risk of rheumatic fever 1, 2
- Do not use sulfonamides or tetracyclines, which have high resistance rates and poor eradication 1
When to Reassess
The child should return to school 12-24 hours after the first dose if afebrile and improved 7. However, reevaluate if: