Adult Amoxicillin Dosing for Strep Throat
For adults with confirmed Group A streptococcal pharyngitis, prescribe amoxicillin 500 mg twice daily for 10 days, or alternatively 1000 mg once daily for 10 days. 1, 2
Standard Dosing Regimens
Two evidence-based options exist for adults:
- Twice-daily dosing: 500 mg every 12 hours for 10 days 1, 2
- Once-daily dosing: 1000 mg (1 gram) once daily for 10 days 1, 3
The American Heart Association has endorsed once-daily amoxicillin dosing, which may improve adherence without compromising efficacy 1, 3. Both regimens have strong, high-quality evidence supporting their use 1.
Critical Treatment Duration
Complete the full 10-day course regardless of symptom improvement. 4, 1 This duration is essential to:
- Achieve maximal pharyngeal eradication of Group A Streptococcus 4, 1
- Prevent acute rheumatic fever, even though this complication is more common in children than adults 4
- Prevent peritonsillar abscess and further spread during outbreaks 4
Patients typically become non-contagious after 24 hours of antibiotic therapy, but stopping treatment early increases treatment failure rates and complication risk 1.
When to Use Amoxicillin
Only prescribe antibiotics after confirming streptococcal infection with rapid antigen detection test and/or throat culture 4. The 2012 IDSA guidelines explicitly recommend antibiotic therapy only for patients with positive streptococcal test results 4.
Amoxicillin remains first-line due to proven efficacy, narrow spectrum, safety, and low cost 5, 1. It is preferred over penicillin V in adults primarily due to better dosing convenience 5, 1.
Alternatives for Penicillin-Allergic Patients
For non-immediate (non-anaphylactic) penicillin allergy:
For immediate/anaphylactic penicillin allergy (avoid all beta-lactams):
- Clindamycin 300-450 mg three times daily for 10 days (preferred due to ~1% resistance rate) 6, 1
- Azithromycin 500 mg once daily for 5 days (be aware of 5-8% macrolide resistance in the U.S.) 6, 1
Up to 10% of patients with immediate penicillin hypersensitivity have cross-reactivity with cephalosporins, so these patients must avoid all beta-lactam antibiotics 6.
Common Pitfalls to Avoid
- Do not prescribe antibiotics without confirming streptococcal infection - over 60% of adults with sore throat receive unnecessary antibiotics, but most pharyngitis is viral 4
- Do not shorten the course below 10 days even if symptoms resolve in 3-4 days - this increases treatment failure and rheumatic fever risk 4, 1
- Do not use amoxicillin-clavulanate (Augmentin) as first-line - plain amoxicillin is appropriate and avoids unnecessary broad-spectrum coverage 5
- Take amoxicillin at the start of meals to minimize gastrointestinal intolerance 2
Adjunctive Symptomatic Treatment
Offer analgesic therapy including aspirin, acetaminophen, NSAIDs, or throat lozenges to reduce pain 4. Antibiotics only shorten sore throat duration by 1-2 days, with modest benefit (number needed to treat = 6 at 3 days, 21 at 1 week) 4.