What is the appropriate amoxicillin dosing for a 10‑kg child with confirmed streptococcal pharyngitis and normal renal function?

Amoxicillin Dosing for a 10‑kg Child with Streptococcal Pharyngitis

For a 10‑kg child with confirmed Group A streptococcal pharyngitis, prescribe amoxicillin 500 mg (50 mg/kg) once daily for 10 days, or alternatively 250 mg (25 mg/kg) twice daily for 10 days.

Weight‑Based Dose Calculation

• Once‑daily regimen: 10 kg × 50 mg/kg = 500 mg once daily (maximum single dose 1,000 mg). 12
• Twice‑daily regimen: 10 kg × 25 mg/kg = 250 mg twice daily (maximum 500 mg per dose). 12
• Both schedules are equally effective and receive strong recommendation with high‑quality evidence from the Infectious Diseases Society of America. 1

Practical Suspension Dosing

• Using 250 mg/5 mL suspension: Give 10 mL once daily (for the 500‑mg dose) or 5 mL twice daily (for the 250‑mg dose). 3
• Using 125 mg/5 mL suspension: Give 20 mL once daily or 10 mL twice daily. 3
• The once‑daily regimen may improve adherence without compromising efficacy. 145

Mandatory Treatment Duration

• Complete the full 10‑day course regardless of symptom improvement to achieve maximal pharyngeal eradication and prevent acute rheumatic fever. 123
• Fever and sore throat typically resolve within 3–4 days, but stopping early increases treatment failure and rheumatic fever risk. 1
• Antibiotic therapy may be started up to 9 days after symptom onset and still effectively prevent acute rheumatic fever. 1

Administration Instructions

• Give amoxicillin at the start of a meal to minimize gastrointestinal intolerance. 3
• After reconstitution, shake the oral suspension well before each use; refrigeration is preferable but not required. 3
• Discard any unused suspension after 14 days. 3

Evidence Supporting This Dosing

• Amoxicillin at 40–50 mg/kg/day achieves superior clinical cure (≈88% vs 71%) and bacteriologic eradication (≈79% vs 55%) compared with lower‑dose penicillin V. 26
• Once‑daily amoxicillin (750 mg in children >40 kg, scaled proportionally for 10 kg) is non‑inferior to twice‑daily dosing, with bacteriologic failure rates of 20.1% vs 15.5% at 14–21 days and 2.8% vs 7.1% at 28–35 days. 4
• No documented penicillin resistance exists worldwide among Group A Streptococcus, ensuring reliable efficacy. 12

Alternatives for Penicillin‑Allergic Patients

Non‑Anaphylactic Penicillin Allergy

• Cephalexin: 200 mg (20 mg/kg) twice daily for 10 days (maximum 500 mg per dose); cross‑reactivity risk is only 0.1%. 12
• Cefadroxil: 300 mg (30 mg/kg) once daily for 10 days (maximum 1 g). 12

Immediate/Anaphylactic Penicillin Allergy

• Clindamycin: 70 mg (7 mg/kg) three times daily for 10 days (maximum 300 mg per dose); resistance ≈1% in the United States. 12
• Azithromycin: 120 mg (12 mg/kg) once daily for 5 days (maximum 500 mg); macrolide resistance 5–8% in the United States. 12
• Avoid all β‑lactams (including cephalosporins) in patients with immediate hypersensitivity due to up to 10% cross‑reactivity. 1

Common Pitfalls to Avoid

• Do not shorten the course below 10 days (except azithromycin's 5‑day regimen), as this markedly increases treatment failure and rheumatic fever risk. 12
• Do not prescribe antibiotics without confirming Group A Streptococcus via rapid antigen detection test or throat culture; most pharyngitis cases are viral. 12
• Do not order routine post‑treatment throat cultures for asymptomatic patients; reserve testing for special circumstances such as history of rheumatic fever. 1

Monitoring and Follow‑Up

• Children on appropriate therapy should show clinical improvement within 48–72 hours; lack of improvement warrants re‑evaluation. 2
• Patients stop being contagious after 24 hours of antibiotic therapy. 2

Adjunctive Symptomatic Treatment

• Offer acetaminophen or ibuprofen for moderate‑to‑severe sore throat or fever. 1
• Avoid aspirin in children due to Reye syndrome risk. 12
• Corticosteroids are not recommended as adjunctive therapy. 1