Amoxicillin Dosage for Streptococcal Infections
For adults with streptococcal pharyngitis, the recommended dose of amoxicillin is 500 mg twice daily for 10 days. 1, 2
Adult Dosing
- Amoxicillin 500 mg twice daily for 10 days is the standard adult dosing regimen 3, 1
- Alternative dosing: 250 mg three or four times daily for 10 days 3
- A full 10-day course is essential to prevent acute rheumatic fever, even if symptoms resolve earlier 1, 2
Pediatric Dosing
- For children weighing less than 40 kg: 50 mg/kg once daily (maximum 1,000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
- For children under 12 weeks of age: 30 mg/kg/day divided every 12 hours due to incompletely developed renal function 2
- Amoxicillin is often preferred over penicillin V in young children due to better taste acceptance of the suspension 3
Administration Considerations
- Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 2
- Patients are generally considered non-contagious after 24 hours of antibiotic therapy 1
- Once-daily dosing may improve adherence compared to multiple daily doses 4, 5
Evidence for Once-Daily Dosing
- Once-daily amoxicillin has been shown to be non-inferior to twice-daily dosing in large clinical trials 4
- The American Heart Association has endorsed once-daily amoxicillin dosing for streptococcal pharyngitis 5
- A meta-analysis found that once-daily amoxicillin maintains efficacy, unlike once-daily penicillin which showed decreased efficacy 6
Alternative Options for Penicillin-Allergic Patients
- For non-immediate penicillin allergy: First-generation cephalosporins (e.g., cephalexin 20 mg/kg twice daily, maximum 500 mg per dose) 7
- For severe or immediate penicillin allergy: Clindamycin (7 mg/kg three times daily, maximum 300 mg per dose) 7
- Macrolides (e.g., azithromycin) can be considered but have concerns about resistance 7
Important Clinical Considerations
- Treatment should continue for at least 10 days to prevent acute rheumatic fever, regardless of symptom resolution 3, 1, 2
- For patients with renal impairment (GFR 10-30 mL/min), adjust dose to 500 mg or 250 mg every 12 hours depending on infection severity 2
- Routine post-treatment throat cultures are not recommended for asymptomatic patients who have completed therapy 7
Common Pitfalls
- Shorter treatment courses (less than 10 days) may lead to treatment failure and risk of rheumatic fever 3, 2
- Macrolide resistance varies geographically and should be considered when selecting alternative treatments 7
- Underdosing amoxicillin may lead to bacteriologic failure; the recommended doses are designed to maintain adequate time above MIC 8
Amoxicillin remains a first-line treatment for streptococcal pharyngitis due to its proven efficacy, safety, narrow spectrum, and low cost 3, 1.