What is the appropriate antibiotic regimen for treating streptococcal pharyngitis in a generally healthy 149‑lb (≈68 kg) adult?

Treatment of Streptococcal Pharyngitis in a 149-lb Adult

For a 149-lb (68 kg) adult with confirmed strep throat, prescribe amoxicillin 500 mg orally twice daily for a full 10 days. 1, 2

First-Line Antibiotic Regimen

• Amoxicillin 500 mg orally twice daily for 10 days is the preferred treatment, offering equal efficacy to penicillin with better palatability and adherence. 1, 2
• Penicillin V 250 mg orally three times daily for 10 days is an equally effective alternative, though amoxicillin's twice-daily dosing improves compliance. 1
• Intramuscular benzathine penicillin G (single injection) is appropriate when oral adherence is uncertain. 1
• No resistance to penicillin or amoxicillin has been documented anywhere in the world among Group A Streptococcus, making these agents uniquely reliable. 1, 2

Critical Treatment Duration

• The full 10-day course is mandatory to achieve maximal pharyngeal eradication and prevent acute rheumatic fever, even if symptoms resolve within 3–4 days. 1, 2
• Shortening the course by even a few days leads to appreciable increases in treatment failure rates and rheumatic fever risk. 3, 2
• Treatment can be initiated up to 9 days after symptom onset and still prevent acute rheumatic fever. 3, 1

Alternative Regimens for Penicillin Allergy

Non-Immediate (Delayed) Penicillin Allergy

• First-generation cephalosporins are the preferred alternatives, with cephalexin 500 mg orally twice daily for 10 days being the specific recommendation. 1, 2
• The cross-reactivity risk is only 0.1% in patients with non-severe, delayed penicillin reactions (e.g., mild rash occurring >1 hour after exposure). 3, 1

Immediate/Anaphylactic Penicillin Allergy

• Clindamycin 300 mg orally three times daily for 10 days is the preferred choice, with only ~1% resistance among U.S. Group A Streptococcus isolates. 3, 2
• All β-lactam antibiotics (including cephalosporins) must be avoided due to up to 10% cross-reactivity risk in patients with anaphylaxis, angioedema, or immediate urticaria. 3, 1
• Azithromycin 500 mg once daily for 5 days is an acceptable alternative, but macrolide resistance ranges from 5–8% in the United States, making it less reliable. 3, 2
• Clarithromycin 250 mg twice daily for 10 days is another macrolide option with similar resistance concerns. 3

Adjunctive Symptomatic Treatment

• Offer acetaminophen or NSAIDs (e.g., ibuprofen) for moderate to severe sore throat or fever. 1, 2
• Corticosteroids are not recommended as adjunctive therapy. 3

Common Pitfalls to Avoid

• Do not prescribe courses shorter 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 the 10% cross-reactivity risk. 3, 1
• Do not assume all penicillin-allergic patients cannot receive cephalosporins—only those with immediate/anaphylactic reactions should avoid them. 2
• Do not order routine post-treatment throat cultures for asymptomatic patients who have completed therapy; testing should be reserved for special circumstances (e.g., history of rheumatic fever). 3

Why These Recommendations

• Amoxicillin and penicillin remain the drugs of choice due to proven efficacy, narrow spectrum of activity, excellent safety profile, low cost, and absence of documented resistance worldwide. 1, 2
• The primary goal of treatment is preventing acute rheumatic fever and suppurative complications, which requires adequate bacterial eradication—not just symptom relief. 3
• Antibiotics shorten symptom duration by only 1–2 days but are critical for preventing serious complications. 3