Penicillin Dosing for Group A Streptococcal Infections
For Group A streptococcal pharyngitis, penicillin V should be dosed at 250 mg twice or three times daily for children, or 250 mg four times daily (or 500 mg twice daily) for adolescents and adults, all for a full 10-day course. 1
Oral Penicillin V Dosing by Age
Children:
- 250 mg twice daily (BID) or three times daily (TID) for 10 days 2, 1
- Both BID and TID regimens yield similar cure rates 3
Adolescents and Adults:
- 250 mg four times daily (QID) for 10 days 2, 1
- OR 500 mg twice daily (BID) for 10 days 2, 1
- The 500 mg BID regimen is equally effective as the 250 mg QID regimen and improves compliance 3
Parenteral Penicillin Dosing
For severe infections or when oral therapy is not feasible:
- Intravenous penicillin: 100,000-250,000 units/kg/day divided every 4-6 hours 2
- Intramuscular benzathine penicillin G: 1.2 million units as a single dose for patients ≥27 kg, or 600,000 units for patients <27 kg 2, 1
- Benzathine penicillin G is preferred when compliance with oral therapy is uncertain 1
Why Penicillin Remains First-Line
Penicillin V is the drug of choice for Group A streptococcal infections due to its proven efficacy, safety, narrow spectrum of activity, and low cost 1. No penicillin resistance has been documented in Group A Streptococcus anywhere in the world 4. The primary goal of treatment is prevention of acute rheumatic fever, which requires adequate bacterial eradication achievable only with a full 10-day course 2, 1.
Critical Treatment Duration
A full 10-day course is mandatory for penicillin therapy to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever 2, 1. Therapy can be safely postponed up to 9 days after symptom onset and still prevent rheumatic fever, allowing time for culture confirmation 2, 1. However, once started, the full 10-day course must be completed even if symptoms resolve earlier 1.
Alternative: Amoxicillin
Amoxicillin is equally effective and often preferred in young children due to better palatability of the suspension 1:
- 50 mg/kg once daily (maximum 1,000 mg) for 10 days 1
- OR 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
Common Pitfalls to Avoid
- Never shorten the course below 10 days - this dramatically increases treatment failure rates and risk of acute rheumatic fever 1, 4
- Do not use sulfonamides or tetracyclines - these have high resistance rates and frequent treatment failures 1
- Avoid prescribing antibiotics without confirming diagnosis - 70% of patients with sore throats receive unnecessary antibiotics nationally; use throat culture or rapid antigen detection test 2
- Do not assume treatment failure means penicillin resistance - penicillin treatment failures (5-35% bacteriologic non-eradication) occur despite universal in vitro susceptibility, likely due to copathogen co-colonization 5