What is the appropriate amoxicillin dose for a 21.59 kg child with streptococcal pharyngitis using a suspension containing 400 mg per 5 mL?

Amoxicillin Dosing for Streptococcal Pharyngitis in a 21.59 kg Child

For this 21.59 kg child with streptococcal pharyngitis, administer 1,080 mg of amoxicillin daily (540 mg twice daily), which equals 6.75 mL of the 400 mg/5 mL suspension twice daily for 10 days. 1

Weight-Based Calculation

• The recommended dose for Group A Streptococcal pharyngitis is 50-75 mg/kg/day divided into 2 doses for 10 days. 2, 1
• For this 21.59 kg patient, using the standard 50 mg/kg/day dosing: 21.59 kg × 50 mg/kg = 1,080 mg total daily dose 1
• This translates to 540 mg per dose, administered twice daily 2, 1
• With the 400 mg/5 mL suspension: (540 mg ÷ 400 mg) × 5 mL = 6.75 mL per dose 1

Alternative Once-Daily Dosing Option

• Once-daily amoxicillin at 750 mg (9.4 mL of 400 mg/5 mL suspension) is an acceptable alternative that improves adherence without compromising efficacy. 2, 3, 4
• The American Heart Association endorses once-daily dosing for streptococcal pharyngitis, and multiple studies demonstrate non-inferiority compared to twice-daily regimens. 3, 4, 5
• Once-daily dosing showed bacteriologic failure rates of 20.1% at 14-21 days versus 15.5% for twice-daily (difference within acceptable margin), with comparable adverse event profiles. 4

Treatment Duration and Monitoring

• Complete the full 10-day course regardless of symptom improvement. 2
• Fever and constitutional symptoms typically resolve within 3-4 days even without treatment, but the full course prevents rheumatic fever. 2
• Therapy can be safely initiated up to 9 days after symptom onset and still prevent acute rheumatic fever. 2
• Patients become non-contagious after 24 hours of antibiotic therapy. 1

Critical Considerations

• Amoxicillin is preferred over penicillin V in young children due to better taste and improved adherence with twice-daily dosing. 1
• The maximum single dose should not exceed 1,000 mg per dose. 2, 1
• For penicillin-allergic patients with non-anaphylactic reactions, narrow-spectrum cephalosporins (cephalexin or cefadroxil) are appropriate alternatives for 10 days. 2, 1
• For Type I penicillin allergy, clindamycin 20 mg/kg/day divided into 3 doses or azithromycin 12 mg/kg once daily for 5 days are alternatives. 2

Common Pitfalls to Avoid

• Do not use subtherapeutic doses below 40 mg/kg/day, as current guidelines recommend 50-75 mg/kg/day for streptococcal infections to ensure adequate coverage. 1
• Verify the suspension concentration before dispensing—the 400 mg/5 mL formulation differs from standard 250 mg/5 mL preparations commonly used. 1
• Do not prescribe antibiotics based solely on clinical presentation without laboratory confirmation (rapid antigen test or culture), as 70% of sore throats in primary care are non-streptococcal. 2
• Shorter 5-7 day courses have shown similar efficacy in some studies but lack sufficient evidence for routine recommendation by major guidelines. 2, 6