Penicillin Dosage for Tonsillitis
For non-allergic patients with tonsillitis, penicillin V should be dosed at 250 mg twice or three times daily for children, and 500 mg twice daily (or 250 mg three to four times daily) for adolescents and adults, for a full 10-day course. 1, 2
Standard Dosing Regimens
Children
- Penicillin V: 250 mg twice or three times daily for 10 days 1
- Weight-based dosing: 40 mg/kg per day divided into 2-3 doses (not to exceed 750 mg for those weighing ≥27 kg) 1
Adolescents and Adults
- Penicillin V: 500 mg twice daily for 10 days (preferred for simplicity) 1
- Alternative: 250 mg three to four times daily for 10 days 1
Alternative: Amoxicillin (Often Preferred in Children)
- Children: 50 mg/kg once daily (maximum 1000 mg) or 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 2
- Amoxicillin is frequently substituted for penicillin V in young children due to better palatability of the suspension, with equivalent efficacy 1, 2
Critical Treatment Duration
The full 10-day course is absolutely essential to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever. 1, 2 Even though symptoms typically resolve within 3-4 days, shortening the course by even a few days results in appreciable increases in treatment failure rates and rheumatic fever risk 1, 2
Therapy can be safely postponed up to 9 days after symptom onset and still prevent rheumatic fever, allowing time for culture confirmation 1, 2
Why Penicillin Remains First-Line
Penicillin V has proven efficacy, narrow spectrum of activity, excellent safety profile, and low cost 1, 2 No penicillin-resistant Group A Streptococcus has ever been documented anywhere in the world, making it uniquely reliable 1, 3, 2
While meta-analyses show cephalosporins may have slightly better bacterial eradication rates than penicillin, the clinical differences are small and not clinically relevant 1, 4
For Penicillin-Allergic Patients
Non-Immediate (Non-Anaphylactic) Allergy
- First-generation cephalosporins are preferred: Cephalexin 20 mg/kg twice daily (maximum 500 mg per dose) or cefadroxil 30 mg/kg once daily (maximum 1 gram) for 10 days 1, 3, 2
- Cross-reactivity risk is only 0.1% in patients with non-severe, delayed penicillin reactions 3, 2
Immediate/Anaphylactic Allergy
- Clindamycin is preferred: 7 mg/kg three times daily (maximum 300 mg per dose) for 10 days in children; 300 mg three times daily for 10 days in adults 1, 3, 2
- Clindamycin has approximately 1% resistance rate among Group A Streptococcus in the United States 1, 3, 2
- Azithromycin alternative: 12 mg/kg once daily (maximum 500 mg) for 5 days 1, 3, 2
- Azithromycin requires only 5 days due to its prolonged tissue half-life, but macrolide resistance is 5-8% in the United States 1, 3, 2
Common Pitfalls to Avoid
- Do not prescribe shorter courses than 10 days (except azithromycin's 5-day regimen), as this dramatically increases treatment failure and rheumatic fever risk 1, 2
- Do not use cephalosporins in patients with immediate/anaphylactic penicillin reactions due to up to 10% cross-reactivity risk 1, 3, 2
- Do not assume all penicillin-allergic patients need to avoid cephalosporins - only those with immediate/anaphylactic reactions should avoid them 3, 2
- Patients are no longer contagious after 24 hours of appropriate antibiotic therapy, but must complete the full 10-day course 1, 2