What is the recommended dose of Amoxicillin (amoxicillin) for treating streptococcal (strep) throat?

Amoxicillin Dosing for Streptococcal Pharyngitis

The recommended dose of amoxicillin for treating streptococcal pharyngitis is 500 mg three times daily for 10 days for adults, or 50 mg/kg/day divided into either once-daily or twice-daily dosing (maximum 1000 mg/day) for 10 days for children. 1, 2

First-Line Treatment Options

Adults:

• Amoxicillin: 500 mg three times daily for 10 days 2
• Alternative amoxicillin dosing: 875 mg twice daily for 10 days 3
• Penicillin V: 250 mg four times daily OR 500 mg twice daily for 10 days 2

Children:

• Amoxicillin: 50 mg/kg/day once daily (maximum 1000 mg) OR 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
• Penicillin V: 250 mg two to three times daily for 10 days (for children) 2

Treatment Duration

The full 10-day course must be completed to prevent complications such as acute rheumatic fever, even if symptoms resolve earlier 1, 3. The FDA label specifically states: "It is recommended that there be at least 10 days' treatment for any infection caused by Streptococcus pyogenes to prevent the occurrence of acute rheumatic fever." 3

Alternative Options for Penicillin-Allergic Patients

For patients with penicillin allergy, alternative treatments include:

• Non-anaphylactic reactions: First-generation cephalosporins for 10 days 2
• Anaphylactic reactions:
  • Clindamycin: 300-450 mg three times daily for 10 days (adults) 2
  • Clarithromycin: 250 mg twice daily for 10 days 2
  • Azithromycin: 500 mg on day 1, then 250 mg daily for 4 days (5 days total) 2, 4

Evidence-Based Considerations

Efficacy of Different Regimens

• Once-daily amoxicillin (50 mg/kg/day, maximum 1000 mg) has been shown to be as effective as penicillin V given three times daily 5, which may improve adherence.
• Ten-day macrolide therapy (clarithromycin) has demonstrated superior streptococcal eradication rates compared to 5-day therapy (azithromycin): 91% vs. 82% 4.
• Twice-daily penicillin dosing (500 mg twice daily) is as effective as four-times-daily dosing, but once-daily dosing showed higher rates of treatment failure 6.

Shorter Courses

While some studies suggest shorter courses (5-7 days) may be effective 7, major guidelines including the Infectious Diseases Society of America (IDSA) continue to recommend the standard 10-day course to prevent complications like acute rheumatic fever 2, 1.

Clinical Pearls and Pitfalls

• Palatability matters: Amoxicillin has better palatability than penicillin V, especially for children, which may improve adherence 1.
• No follow-up cultures needed: Routine post-treatment throat cultures are not recommended if symptoms resolve 2.
• Treatment failure: If no improvement within 48-72 hours, reassess the diagnosis 1.
• Household contacts: Routine testing or treatment of asymptomatic household contacts is not recommended 2.

Important Monitoring

• Assess for clinical improvement within 48-72 hours of starting treatment
• Monitor for adverse effects such as diarrhea, rash, or allergic reactions
• Ensure completion of the full 10-day course even if symptoms resolve quickly

Remember that completing the full 10-day course is critical for preventing acute rheumatic fever, which is the primary reason for treating streptococcal pharyngitis with antibiotics.