Amoxicillin Dosing for Streptococcal Pharyngitis
For this 24.6 kg child with strep throat, administer amoxicillin suspension 1230 mg once daily (approximately 24.6 mL of the 250 mg/5 mL suspension) for 10 days, or alternatively 615 mg twice daily (approximately 12.3 mL twice daily).
Dosing Calculation
The IDSA guideline for group A streptococcal pharyngitis recommends 50 mg/kg once daily (maximum 1000 mg) or alternatively 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1, 2.
For this 24.6 kg child:
Once-daily dosing: 50 mg/kg × 24.6 kg = 1230 mg once daily
- Using 250 mg/5 mL suspension = 24.6 mL once daily
Twice-daily alternative: 25 mg/kg × 24.6 kg = 615 mg twice daily
- Using 250 mg/5 mL suspension = 12.3 mL twice daily
Evidence Supporting Once-Daily Dosing
Once-daily amoxicillin is equally effective as multiple-daily dosing for streptococcal pharyngitis. Multiple high-quality studies demonstrate non-inferiority of once-daily regimens:
A randomized trial of 353 children showed once-daily amoxicillin (1500 mg or 750 mg if ≤30 kg) was non-inferior to twice-daily penicillin V for GABHS eradication, with treatment failures of only 5.8% at days 3-6 3
Another study of 152 children found once-daily amoxicillin (750 mg) had only 5% bacteriologic failure compared to 11% with penicillin V three times daily 4
Real-time PCR analysis confirmed once-daily dosing achieved comparable bacterial eradication to twice- or three-times-daily regimens 5
Key Clinical Points
Duration: Complete the full 10-day course regardless of symptom improvement. This duration is critical to prevent acute rheumatic fever 1, 2, 6.
Practical administration: The FDA label specifies that suspension should be placed directly on the child's tongue or mixed with formula, milk, fruit juice, water, or cold drinks and taken immediately 6. Shake well before each use.
Storage: After reconstitution, refrigeration is preferable but not required. Discard unused suspension after 14 days 6.
Common Pitfalls to Avoid
Underdosing: Many clinicians use lower doses (20-40 mg/kg/day), but the IDSA specifically recommends 50 mg/kg once daily for optimal efficacy 1, 2. Studies show that 40 mg/kg/day amoxicillin was significantly more effective than conventional lower-dose penicillin V 7.
Premature discontinuation: Emphasize completing the full 10 days even when symptoms resolve quickly, as this prevents rheumatic fever.
Azithromycin use: Avoid azithromycin as an alternative—it shows inferior eradication rates, higher recurrence, and increased adverse events compared to amoxicillin 8.
Alternative for Penicillin Allergy
If the patient has a non-anaphylactic penicillin allergy, use cephalexin 20 mg/kg/dose twice daily (maximum 500 mg/dose) for 10 days 1.
If anaphylactic-type allergy, use clindamycin 7 mg/kg/dose three times daily (maximum 300 mg/dose) for 10 days 1, 2.