Antibiotic Dosing for Group A Streptococcal Pharyngitis in a 15-Year-Old (≈53 kg)
First-Line Treatment: Amoxicillin
For a 15-year-old adolescent weighing approximately 53 kg with confirmed Group A streptococcal pharyngitis, prescribe amoxicillin 500 mg orally twice daily for a full 10 days. 1
Why Amoxicillin is the Drug of Choice
- Amoxicillin is the preferred first-line agent due to proven efficacy, narrow antimicrobial spectrum, excellent safety profile, low cost, and the complete absence of documented penicillin resistance in Group A Streptococcus anywhere in the world. 1, 2
- Amoxicillin and penicillin V have identical efficacy against Group A Streptococcus, but amoxicillin offers better palatability and is often preferred in adolescents. 2
Alternative: Penicillin V
- If amoxicillin is unavailable, prescribe penicillin V 500 mg orally twice daily for 10 days (or 250 mg three to four times daily for 10 days). 3, 4
- The FDA-approved dosing for adolescents and adults with streptococcal infections is 250 to 500 mg every 6 to 8 hours for 10 days. 4
Critical Treatment Duration Requirement
- A complete 10-day course is mandatory to achieve maximal pharyngeal eradication of Group A Streptococcus and prevent acute rheumatic fever, even if symptoms resolve within 3 to 4 days. 2, 1
- Shortening the course by even a few days results in appreciable increases in treatment failure rates and dramatically raises the risk of acute rheumatic fever. 2, 1
Treatment for Penicillin-Allergic Patients
Non-Immediate (Delayed) Penicillin Allergy
If the patient has a non-immediate penicillin allergy (e.g., mild delayed rash), prescribe cephalexin 500 mg orally twice daily for 10 days. 1, 2
- First-generation cephalosporins are the preferred alternative for non-immediate penicillin allergy, with strong, high-quality evidence supporting their efficacy. 2, 1
- The cross-reactivity risk with first-generation cephalosporins is only 0.1% in patients with non-severe, delayed penicillin reactions. 2
Immediate/Anaphylactic Penicillin Allergy
If the patient has an immediate or anaphylactic penicillin allergy (anaphylaxis, angioedema, respiratory distress, or urticaria within 1 hour), prescribe clindamycin 300 mg orally three times daily for 10 days. 1, 2
- Patients with immediate hypersensitivity must avoid all beta-lactam antibiotics, including cephalosporins, due to up to 10% cross-reactivity risk. 2, 3
- Clindamycin has only ~1% resistance among Group A Streptococcus in the United States and demonstrates high efficacy even in chronic carriers. 2, 1
Alternative for Immediate Allergy: Azithromycin
If clindamycin cannot be used, prescribe azithromycin 500 mg orally once daily for 5 days. 5, 2
- Azithromycin is the only antibiotic requiring just 5 days due to its prolonged tissue half-life. 2, 5
- However, macrolide resistance among Group A Streptococcus is 5–8% in the United States and varies geographically, making clindamycin more reliable. 2, 1
- The FDA-approved pediatric dosing for pharyngitis/tonsillitis is 12 mg/kg once daily for 5 days (maximum 500 mg), which translates to 500 mg daily for this 53 kg adolescent. 5
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. 2, 1
- Do not assume all penicillin-allergic patients cannot receive cephalosporins—only those with immediate/anaphylactic reactions should avoid them. 2, 1
- Do not use trimethoprim-sulfamethoxazole (Bactrim) for strep throat, as sulfonamides fail to eradicate Group A Streptococcus in 20–25% of cases. 2
- Do not use tetracyclines due to high resistance rates and frequent failure to eradicate even susceptible organisms. 3
Adjunctive Symptomatic Therapy
- Consider acetaminophen or NSAIDs (such as ibuprofen) for moderate to severe symptoms or high fever. 1, 2
- Avoid aspirin in children and adolescents due to the risk of Reye syndrome. 2, 1
- Do not use corticosteroids as adjunctive therapy. 2