What is the first‑line antibiotic choice and dosing for streptococcal pharyngitis in an otherwise healthy 17‑year‑old female without a penicillin allergy?

First-Line Treatment for Streptococcal Pharyngitis in a 17-Year-Old Female

For an otherwise healthy 17-year-old female without penicillin allergy, prescribe oral amoxicillin 1000 mg once daily (or 500 mg twice daily) for a full 10-day course. 1

Recommended Antibiotic Regimen

• Amoxicillin is the drug of choice at a dose of 1000 mg once daily or 500 mg twice daily for 10 days, offering proven efficacy, narrow spectrum, excellent safety, and low cost. 1, 2
• Penicillin V 250 mg orally every 6–8 hours for 10 days is equally effective but less palatable and requires more frequent dosing. 3, 4
• No documented penicillin resistance exists anywhere in the world among Group A Streptococcus, ensuring reliable bacterial eradication with amoxicillin. 1, 2

Critical Treatment Duration

• 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 3–4 days. 1, 5
• Shortening the regimen by even a few days leads to appreciable increases in treatment-failure rates and rheumatic fever risk. 1, 5

Diagnostic Confirmation Before Treatment

• Confirm Group A Streptococcus infection with a rapid antigen detection test (RADT) or throat culture before prescribing antibiotics, as clinical features alone cannot reliably differentiate bacterial from viral pharyngitis. 1, 6
• A positive RADT is diagnostic and does not require backup culture. 1
• A negative RADT in adolescents should be followed by throat culture to avoid missing true infections. 1, 4

Alternative Regimens for Penicillin Allergy

Non-Immediate (Delayed) Penicillin Allergy

• First-generation cephalosporins are preferred alternatives with strong, high-quality evidence: cephalexin 500 mg twice daily or cefadroxil 1 gram once daily for 10 days. 1, 5
• Cross-reactivity risk with first-generation cephalosporins is only 0.1% in patients with delayed, mild penicillin reactions. 1, 5

Immediate/Anaphylactic Penicillin Allergy

• Clindamycin 300 mg orally three times daily for 10 days is the optimal choice for patients with anaphylaxis, angioedema, or immediate urticaria to penicillin, with only ~1% resistance among U.S. Group A Streptococcus isolates. 1, 5
• All beta-lactams must be avoided in immediate hypersensitivity reactions due to up to 10% cross-reactivity risk. 1, 5
• Azithromycin 500 mg once daily for 5 days is an acceptable alternative, but macrolide resistance ranges from 5–8% in the United States and varies geographically. 1, 2

Symptomatic Management

• Offer acetaminophen or NSAIDs (ibuprofen) for moderate to severe sore throat, fever, or systemic discomfort. 1, 5
• Avoid aspirin in adolescents due to Reye syndrome risk. 1, 5
• Corticosteroids are not recommended as adjunctive therapy. 1, 2

Common Pitfalls to Avoid

• Do not prescribe antibiotics without diagnostic confirmation via RADT or throat culture, as most pharyngitis cases are viral. 1, 6
• Do not use cephalosporins in patients with immediate/anaphylactic penicillin reactions due to the ~10% cross-reactivity risk. 1, 5
• Do not shorten the antibiotic course below 10 days (except azithromycin's 5-day regimen), as this markedly increases treatment failure and rheumatic fever risk. 1, 5
• Do not order routine post-treatment throat cultures for asymptomatic patients who have completed therapy; reserve testing for special circumstances such as history of rheumatic fever. 1

When to Reassess

• Patients with worsening symptoms after appropriate antibiotic initiation or with symptoms lasting 5 days after starting treatment should be reevaluated for alternative diagnoses or complications. 6