Amoxicillin for Strep Throat
For strep throat, amoxicillin should be dosed at 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for children, and 500 mg twice daily for adults, with treatment continued for a full 10 days to prevent acute rheumatic fever. 1, 2
Dosing by Age Group
Children (≥3 months and <40 kg)
- 50 mg/kg once daily (maximum 1000 mg) for 10 days is the preferred regimen 1, 2
- Alternative: 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 2
- For severe infections: 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours 3
Adolescents and Adults (≥40 kg)
Infants (<3 months)
- Maximum 30 mg/kg/day divided every 12 hours due to immature renal function 3
- Full 10-day course required 3
Critical Treatment Principles
The complete 10-day course must be finished even if symptoms resolve earlier, as this is essential to prevent acute rheumatic fever. 1, 2, 3 This recommendation carries a "strong, high" evidence rating from the Infectious Diseases Society of America 1.
- Patients become non-contagious after 24 hours of antibiotic therapy 5, 2
- Treatment should be started at the beginning of a meal to minimize gastrointestinal side effects 3
Why Amoxicillin Over Penicillin V
While penicillin V remains the traditional first-line agent, amoxicillin offers several advantages 1:
- Once-daily dosing improves adherence, particularly important for completing the full 10-day course 1, 2
- More palatable suspension for children 1
- Equal efficacy to penicillin V 1
- Narrow spectrum with low cost 1, 2
Research demonstrates that amoxicillin at 40 mg/kg/day achieves superior bacteriologic cure rates (79.3%) compared to standard-dose penicillin V (54.5%), suggesting that adequate dosing is critical 6.
Penicillin-Allergic Patients
For patients with true penicillin allergy 1, 2:
- First-generation cephalosporin (if no anaphylactic history): Cephalexin 20 mg/kg twice daily (maximum 500 mg per dose) for 10 days
- Clindamycin: 7 mg/kg three times daily (maximum 300 mg per dose) for 10 days
- Azithromycin: 12 mg/kg once daily (maximum 500 mg) for 5 days—note that macrolide resistance varies geographically 1, 2
- Clarithromycin: 7.5 mg/kg twice daily (maximum 250 mg per dose) for 10 days
Renal Impairment Dosing
For patients with severe renal impairment 3:
- GFR 10-30 mL/min: 250-500 mg every 12 hours (do NOT use 875 mg dose)
- GFR <10 mL/min: 250-500 mg every 24 hours
- Hemodialysis: 250-500 mg every 24 hours, with additional dose during and after dialysis
Common Pitfalls to Avoid
- Do not use shorter courses: While some research suggests 5-7 day courses may be effective 7, 8, current guidelines do not endorse this due to insufficient comprehensive evidence supporting prevention of rheumatic fever 1
- Ensure adequate dosing: Underdosing may explain perceived penicillin treatment failures 6
- Do not routinely test or treat asymptomatic household contacts 1
- Follow-up cultures are not routinely needed unless symptoms persist 1, 4
Oral Suspension Preparation
After reconstitution, the suspension remains stable for 14 days; refrigeration is preferable but not required 3. Shake well before each use and administer directly or mix with formula, milk, or juice (consume immediately) 3.