What is the recommended amoxicillin dosage for a 10‑day course in an adult with uncomplicated streptococcal pharyngitis and normal renal function?

Amoxicillin Dosing for Streptococcal Pharyngitis in Adults

For an adult with streptococcal pharyngitis and normal renal function, prescribe amoxicillin 500 mg orally twice daily for a full 10‑day course. 1

Standard Adult Dosing Regimen

• Amoxicillin 500 mg orally every 12 hours for 10 days is the recommended regimen for adolescents and adults with confirmed Group A Streptococcal pharyngitis. 1
• An alternative once‑daily regimen of 1000 mg (1 gram) once daily for 10 days is equally effective and may improve adherence, recently endorsed by the American Heart Association. 1, 2
• Both regimens achieve comparable bacteriologic eradication rates (approximately 85–95%) and clinical cure rates. 3, 4, 5

Critical Treatment Duration

• The full 10‑day course is mandatory to achieve maximal pharyngeal eradication of Group A Streptococcus and to prevent acute rheumatic fever, even if symptoms resolve within 3–4 days. 6, 1
• Shortening the course by even a few days results in appreciable increases in treatment‑failure rates and rheumatic‑fever risk. 6
• Patients become non‑contagious after 24 hours of antibiotic therapy but must complete the entire 10‑day regimen. 7

Why Amoxicillin Is First‑Line

• Amoxicillin remains the drug of choice due to proven efficacy, narrow antimicrobial spectrum, excellent safety profile, low cost, and the complete absence of documented penicillin resistance in Group A Streptococcus worldwide. 6, 1
• Amoxicillin is preferred over penicillin V in clinical practice because of better palatability and more convenient dosing schedules (twice daily vs. three to four times daily). 6

Once‑Daily vs. Twice‑Daily Dosing

• Meta‑analyses and randomized controlled trials demonstrate that once‑daily amoxicillin (750–1000 mg) is non‑inferior to twice‑daily dosing for bacteriologic eradication and clinical cure. 3, 4, 5
• Once‑daily dosing may enhance adherence without compromising efficacy, making it a suitable alternative when compliance is a concern. 3, 5, 2
• In contrast, once‑daily penicillin V is associated with a 12 percentage‑point lower cure rate compared with more frequent dosing and should not be used. 8

Alternative Regimens for Penicillin Allergy

• For non‑immediate (delayed) penicillin allergy: First‑generation cephalosporins such as cephalexin 500 mg twice daily for 10 days are preferred, with only 0.1% cross‑reactivity risk. 6
• For immediate/anaphylactic penicillin allergy: Clindamycin 300 mg three times daily for 10 days is the optimal choice, with approximately 1% resistance among U.S. Group A Streptococcus isolates and superior eradication in chronic carriers. 6
• Azithromycin 500 mg once daily for 5 days is an acceptable alternative, but macrolide resistance in the United States ranges from 5% to 8% and varies geographically. 6
• All beta‑lactam antibiotics (including cephalosporins) must be avoided in patients with immediate hypersensitivity reactions due to up to 10% cross‑reactivity risk. 6

Dosing in Renal Impairment

• Patients with glomerular filtration rate (GFR) 10–30 mL/min: Reduce dose to 500 mg or 250 mg every 12 hours, depending on infection severity. 9
• Patients with GFR <10 mL/min or on hemodialysis: Reduce dose to 500 mg or 250 mg every 24 hours, with an additional dose both during and at the end of dialysis. 9
• The 875 mg dose should not be used in patients with severe renal impairment (GFR <30 mL/min). 9

Administration and Adherence

• Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance. 9
• Emphasize to patients that completing the full 10‑day course is essential to prevent acute rheumatic fever, even if symptoms improve rapidly. 6, 1

Common Pitfalls to Avoid

• Do not prescribe shorter courses than 10 days (except azithromycin's 5‑day regimen), as this markedly increases treatment failure and rheumatic‑fever risk. 6
• Do not use trimethoprim‑sulfamethoxazole (Bactrim) for streptococcal pharyngitis, as it fails to eradicate Group A Streptococcus in 20–25% of cases. 6
• Do not order routine post‑treatment throat cultures for asymptomatic patients who have completed therapy; reserve testing for special circumstances such as a history of rheumatic fever. 6

Adjunctive Symptomatic Treatment

• Offer acetaminophen or NSAIDs (e.g., ibuprofen) for moderate to severe sore throat, fever, or systemic discomfort. 6
• Avoid aspirin in children due to the risk of Reye syndrome. 6
• Corticosteroids are not recommended as adjunctive therapy. 6