Amoxicillin Dosing for Tonsillitis
For pediatric patients with confirmed Group A streptococcal tonsillitis, prescribe amoxicillin 50 mg/kg once daily (maximum 1000 mg) for 10 days; for adults, prescribe 500 mg twice daily or 250 mg four times daily for 10 days. 1, 2
Pediatric Dosing (≥3 months and <40 kg)
Preferred regimen:
- Amoxicillin 50 mg/kg once daily (maximum 1000 mg) for 10 days is the first-line treatment, offering superior adherence while maintaining equivalent efficacy to multiple-daily dosing for eradication of Streptococcus pyogenes. 1, 2
Alternative regimens when once-daily dosing is not feasible:
- Amoxicillin 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days provides comparable total daily dosing (~950 mg/day). 1, 2
- For mild-to-moderate infections: 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours. 3
- For severe infections: 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours. 3
Infants <3 months:
- Maximum dose is 30 mg/kg/day divided every 12 hours due to immature renal function. 3
Adult Dosing (≥40 kg)
Standard regimens:
- Penicillin V 500 mg twice daily for 10 days remains the traditional first-line option. 1, 2
- Amoxicillin 500 mg every 12 hours or 250 mg every 8 hours for 10 days for mild-to-moderate infections. 3
- Amoxicillin 875 mg every 12 hours or 500 mg every 8 hours for 10 days for severe infections. 3
Critical Treatment Duration
A complete 10-day course is mandatory for all penicillin and amoxicillin regimens to prevent acute rheumatic fever, regardless of early symptom resolution (typically within 24-48 hours). 1, 2 Shortened courses (<10 days) demonstrate inferior bacteriological eradication and clinical cure rates. 1
Penicillin Allergy Alternatives
Non-anaphylactic allergy (e.g., hives):
- Cephalexin 20 mg/kg twice daily (maximum 500 mg per dose) for 10 days is the preferred alternative, with minimal cross-reactivity risk (~10%). 1, 2
- Cefadroxil 30 mg/kg once daily (maximum 1 g) for 10 days is an acceptable once-daily cephalosporin option. 1, 2
Anaphylactic or severe immediate-type allergy:
- Clindamycin 7 mg/kg three times daily (maximum 300 mg per dose) for 10 days is the most reliable option, with only ~1% resistance among U.S. GAS isolates. 1, 2
- Azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days may be used, but macrolide resistance ranges from 5-8% nationally and may exceed 37% in some regions. 1, 2
- Clarithromycin 7.5 mg/kg twice daily (maximum 250 mg per dose) for 10 days shares the same resistance concerns as azithromycin. 1, 2
Renal Impairment Dosing (Adults and Pediatric >40 kg)
Severe renal impairment requires dose reduction: 3
- GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours (do NOT use 875 mg dose)
- GFR <10 mL/min: 500 mg or 250 mg every 24 hours
- Hemodialysis: 500 mg or 250 mg every 24 hours, with an additional dose during and at the end of dialysis
Essential Clinical Considerations
Diagnostic confirmation is required before initiating antibiotics:
- Only 20-30% of children and 10% of adults with pharyngitis actually have GAS infection. 1
- Initiate treatment only after positive rapid antigen detection test (RADT) or throat culture. 1, 2
- In children, a negative RADT requires confirmatory throat culture; in adults, negative RADT alone is sufficient. 1
Administration guidance:
- Take amoxicillin at the start of a meal to minimize gastrointestinal intolerance. 3
Common pitfalls to avoid:
- Never exceed 1000 mg/day for once-daily pediatric dosing or 500 mg per dose for twice-daily regimens. 1
- Do not use once-daily penicillin V (results in 12 percentage-point lower cure rate compared to twice- or thrice-daily dosing). 1
- Do not avoid first-generation cephalosporins in non-anaphylactic penicillin allergy; cross-reactivity risk is minimal and guidelines explicitly endorse their use. 1, 2
- Routine post-treatment throat cultures are not indicated in uncomplicated cases. 1
Symptomatic management: