Amoxicillin Dosing for Streptococcal Pharyngitis in a 48-Pound Child
For a 48-pound (21.8 kg) pediatric patient with streptococcal pharyngitis, administer amoxicillin 1,000 mg once daily OR 500 mg twice daily for 10 days. 1, 2, 3, 4
Weight-Based Calculation
A 48-pound child weighs approximately 21.8 kg. Using the guideline-recommended dosing:
- Preferred regimen: 50 mg/kg once daily = 1,090 mg, which rounds to the maximum of 1,000 mg once daily 1, 2, 3, 4
- Alternative regimen: 25 mg/kg twice daily = 545 mg per dose, which rounds to 500 mg twice daily 1, 2, 3, 4
- Duration: Complete the full 10-day course regardless of symptom resolution to prevent acute rheumatic fever 1, 3, 4
Why Amoxicillin Over Penicillin V
Amoxicillin is superior to penicillin V for streptococcal pharyngitis. The IDSA guidelines establish amoxicillin as the preferred first-line oral antibiotic with strong, high-quality evidence. 3 Research demonstrates that amoxicillin at 40 mg/kg/day achieves significantly better bacteriologic cure rates (79.3%) compared to standard-dose penicillin V (54.5%, P = 0.005) and better clinical cure rates (87.9% vs 70.9%, P = 0.025). 5
Critical Administration Details
- Timing: Administer at the start of a meal to minimize gastrointestinal intolerance 4
- Non-contagious period: The child becomes non-contagious after 24 hours of antibiotic therapy 6
- Compliance advantage: Once-daily dosing significantly improves adherence compared to multiple daily doses 7
When Standard Amoxicillin Fails
If this patient has treatment failure or is a chronic Group A Streptococcus carrier, switch to amoxicillin/clavulanate (Augmentin):
- Dose: 40 mg/kg/day of the amoxicillin component divided into 3 doses (maximum 2,000 mg/day) for 10 days 1, 2
- For this 21.8 kg child: Approximately 290 mg three times daily 1
Penicillin Allergy Alternatives
For documented penicillin allergy, use these alternatives:
- Cephalexin: 20 mg/kg/dose twice daily (maximum 500 mg/dose) = approximately 440 mg twice daily for this child 1, 3
- Clindamycin: 7 mg/kg/dose three times daily (maximum 300 mg/dose) = approximately 150 mg three times daily 1, 3
- Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days = approximately 260 mg once daily, though use with caution due to resistance 1, 3
Avoid cephalosporins in patients with immediate (Type I) hypersensitivity to penicillin. 3
Common Pitfalls to Avoid
- Do not use azithromycin as first-line therapy: Resistance rates vary geographically, and bacteriologic eradication is inferior (65% vs 82% with penicillin V, P < 0.001) 8, 9
- Do not stop antibiotics early: Even if symptoms resolve in 2-3 days, complete the full 10-day course to prevent acute rheumatic fever 1, 3, 4
- Do not use amoxicillin/clavulanate as first-line: Reserve this for treatment failures or chronic carriers only 1, 2, 3
- Do not perform routine post-treatment testing: Follow-up throat cultures are not recommended unless specific circumstances exist 1
Monitoring Response
- Assess clinical response at 48-72 hours: If no improvement, consider treatment failure and alternative antibiotics 2, 3
- Consider local resistance patterns: Particularly important for macrolides in your geographic area 3
- Evaluate recent antibiotic exposure: Use within the previous 4-6 weeks increases risk of resistant organisms 3