What is the recommended dose of amoxicillin (amoxicillin) for an 8-year-old patient weighing 32 kg with strep pharyngitis?

Amoxicillin Dosing for Strep Pharyngitis in an 8-Year-Old (32 kg)

For this 8-year-old child weighing 32 kg with strep pharyngitis, prescribe amoxicillin 50 mg/kg once daily (1600 mg, rounded to 1000 mg maximum) OR 25 mg/kg twice daily (800 mg per dose, rounded to 500 mg twice daily) for a full 10 days. 1, 2, 3

Specific Dosing Calculation

For this patient:

• Once-daily dosing: 50 mg/kg × 32 kg = 1600 mg, but maximum dose is 1000 mg once daily 2, 4
• Twice-daily dosing: 25 mg/kg × 32 kg = 800 mg/day ÷ 2 = 400 mg per dose, rounded to 500 mg twice daily 1, 2, 3

Either regimen is equally effective—choose based on adherence concerns. Once-daily dosing may improve compliance, while twice-daily dosing follows traditional recommendations. 2, 4, 5

Critical Treatment Requirements

• Complete the full 10-day course regardless of symptom improvement to prevent acute rheumatic fever, even though symptoms typically resolve within 3-4 days 1, 2, 3
• The child becomes non-contagious after 24 hours of antibiotics but must continue treatment for the full duration 2, 4
• Administer at the start of meals to minimize gastrointestinal side effects 3

Evidence Supporting Once-Daily Dosing

Once-daily amoxicillin is non-inferior to twice-daily dosing with comparable bacteriologic cure rates (80-85% eradication at follow-up) and similar adverse event profiles. 5, 6 The Infectious Diseases Society of America endorses this regimen with "strong, high" quality evidence. 1, 2

A large randomized controlled trial of 652 children demonstrated bacteriologic failure rates of 20.1% for once-daily versus 15.5% for twice-daily at 14-21 days, with the difference falling within the prespecified non-inferiority margin. 5 By 28-35 days, once-daily actually showed lower failure rates (2.8% vs 7.1%). 5

Why Amoxicillin Over Penicillin V

Amoxicillin is preferred over penicillin V because:

• Better absorption and higher serum levels 1
• More convenient dosing (once or twice daily vs. 3-4 times daily for penicillin) 1, 7
• Narrow spectrum, proven efficacy, excellent safety profile, and low cost 1, 2
• No documented resistance of Group A Streptococcus to penicillin/amoxicillin anywhere in the world 8

Common Pitfalls to Avoid

• Never shorten the course below 10 days—even a few days less dramatically increases treatment failure and rheumatic fever risk 8, 2
• Do not use once-daily penicillin V—it has 12 percentage points lower cure rate compared to more frequent dosing (unlike amoxicillin, which is effective once daily) 7
• Do not prescribe amoxicillin-clavulanate for uncomplicated strep throat—plain amoxicillin is first-line; the combination is reserved for recurrent cases or suspected resistance 2
• Do not use trimethoprim-sulfamethoxazole (Bactrim)—it has 50% resistance rates and is not recommended for Group A Streptococcus 8

Alternative Regimens (If Penicillin Allergy)

If this patient had a non-immediate penicillin allergy (delayed rash, not anaphylaxis):

• Cephalexin 20 mg/kg/dose twice daily (640 mg/dose, rounded to 500 mg twice daily) for 10 days 8, 4

If immediate/anaphylactic penicillin allergy (avoid all beta-lactams):

• Clindamycin 7 mg/kg/dose three times daily (224 mg/dose, rounded to 300 mg three times daily) for 10 days—only ~1% resistance in US 8, 4
• Azithromycin 12 mg/kg once daily (384 mg, rounded to 500 mg maximum) for 5 days—but 5-8% macrolide resistance in US 8, 4

Adjunctive Therapy

• Consider acetaminophen or ibuprofen for moderate to severe throat pain or high fever 1, 8
• Never use aspirin in children due to Reye syndrome risk 1, 8
• Do not prescribe corticosteroids—they are not recommended for strep pharyngitis 1, 8