What is the recommended dose of amoxicillin for a child with strep throat and a urinary tract infection, considering their weight and potential penicillin allergy?

Amoxicillin Dosing for Pediatric Strep Throat and Urinary Tract Infection

Primary Recommendation for Strep Throat

For children without penicillin allergy, amoxicillin should be dosed at 50 mg/kg once daily (maximum 1,000 mg) for 10 days to treat strep throat. 1

• This dosing regimen has a strong recommendation with high-quality evidence from the Infectious Diseases Society of America (IDSA) guidelines 1
• An alternative regimen is 25 mg/kg twice daily (maximum 500 mg per dose) for 10 days 1
• The once-daily dosing offers superior compliance while maintaining equivalent efficacy 2

Weight-Based Calculation Example

• For a child weighing 20 kg: 50 mg/kg × 20 kg = 1,000 mg once daily 1
• For a child weighing 15 kg: 50 mg/kg × 15 kg = 750 mg once daily 1
• For a child weighing 10 kg: 50 mg/kg × 10 kg = 500 mg once daily 1

Dosing for Urinary Tract Infection

For uncomplicated urinary tract infections in children, amoxicillin should be dosed at 25 mg/kg/day in divided doses every 12 hours or 20 mg/kg/day in divided doses every 8 hours for mild to moderate infections. 3

• For severe genitourinary tract infections, increase to 45 mg/kg/day in divided doses every 12 hours or 40 mg/kg/day in divided doses every 8 hours 3
• Treatment duration should be a minimum of 48-72 hours beyond symptom resolution 3

Important Caveat for UTI Treatment

• Amoxicillin is only effective against β-lactamase-negative E. coli strains 3
• Given increasing resistance patterns, amoxicillin is generally not recommended as first-line therapy for UTI in current practice
• Consider alternative agents (cephalosporins, trimethoprim-sulfamethoxazole) unless culture confirms susceptibility 3

Management with Penicillin Allergy

For children with penicillin allergy, the choice of alternative antibiotic depends on the type of allergic reaction:

Non-Immediate Hypersensitivity (Non-Anaphylactic)

• Cephalexin 20 mg/kg per dose twice daily (maximum 500 mg per dose) for 10 days 1
• Cefadroxil 30 mg/kg once daily (maximum 1 g) for 10 days 1
• Both have strong recommendations with high-quality evidence 1

Immediate Hypersensitivity (Anaphylaxis History)

• Avoid all cephalosporins due to cross-reactivity risk 1
• Clindamycin 7 mg/kg per dose three times daily (maximum 300 mg per dose) for 10 days 1
• Azithromycin 12 mg/kg once daily (maximum 500 mg) for 5 days 1
• Clarithromycin 7.5 mg/kg per dose twice daily (maximum 250 mg per dose) for 10 days 1

Critical Warning About Macrolides

• Resistance of group A streptococcus to azithromycin and clarithromycin varies geographically and temporally 1
• These agents have only moderate-quality evidence compared to high-quality evidence for penicillins 1
• Consider local resistance patterns before prescribing macrolides 1

Treatment Duration and Monitoring

All strep throat treatment must continue for a full 10 days to prevent acute rheumatic fever, regardless of symptom resolution. 1, 3

• This is a non-negotiable requirement for group A streptococcal infections 1
• Children should show clinical improvement within 48-72 hours 4
• If no improvement occurs by 48-72 hours, reevaluation is necessary 4

Common Pitfalls to Avoid

• Never use once-daily penicillin V for strep throat—it has significantly higher failure rates (23% vs 8%) compared to twice-daily dosing 5
• Do not underdose amoxicillin—the 40 mg/kg/day regimen shows inferior bacteriologic cure rates (54.5%) compared to 50 mg/kg/day (79.3%) 6
• Do not use amoxicillin empirically for UTI without culture confirmation of susceptibility, as resistance is common 3
• Always complete the full 10-day course for strep throat, even if symptoms resolve earlier 1, 3

Administration Considerations

• Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance 3
• Oral suspension must be shaken well before each use 3
• Reconstituted suspension remains stable for 14 days; refrigeration is preferable but not required 3