What is the recommended dose of amoxicillin (amoxycillin) for a child with a bacterial infection?

Amoxicillin Dosing for Children

For most bacterial infections in children, amoxicillin should be dosed at 45 mg/kg/day divided into 2 doses for mild-to-moderate infections, or 90 mg/kg/day divided into 2 doses for severe infections or areas with high pneumococcal resistance, with a maximum daily dose of 4000 mg. 1, 2

Standard Dosing Algorithm

Mild-to-Moderate Infections

• 45 mg/kg/day divided every 12 hours is the standard dose for uncomplicated respiratory tract infections, skin infections, and genitourinary infections in children ≥3 months old and weighing <40 kg 1, 3
• This dosing provides adequate coverage for most susceptible pathogens including Streptococcus pneumoniae, Haemophilus influenzae (non-β-lactamase producing), and Streptococcus pyogenes 1, 2

Severe Infections or High-Resistance Areas

• 90 mg/kg/day divided every 12 hours is recommended for:
  • Community-acquired pneumonia in areas with >10% penicillin-resistant S. pneumoniae 1
  • Children <2 years old 1
  • Recent antibiotic exposure within the past 30 days 1
  • Children attending daycare 1
  • Severe infections requiring hospitalization 1, 2

Age-Specific Considerations

• Infants <3 months (12 weeks): Maximum dose is 30 mg/kg/day divided every 12 hours due to immature renal function 3
• Children ≥3 months and <40 kg: Use weight-based dosing as above 1, 3
• Children ≥40 kg: Use adult dosing (500 mg every 12 hours for mild infections; 875 mg every 12 hours for severe infections) 3

Indication-Specific Dosing

Community-Acquired Pneumonia

• Outpatient, mild-to-moderate: 45 mg/kg/day divided every 12 hours 1, 2
• Severe or high resistance: 90 mg/kg/day divided every 12 hours 1, 2
• High-dose therapy is preferable given the prevalence of penicillin-resistant pneumococci 1

Acute Bacterial Sinusitis

• Standard dose: 45 mg/kg/day divided every 12 hours for children ≥2 years without risk factors 1
• High dose: 80-90 mg/kg/day divided every 12 hours for children <2 years, in daycare, or with recent antibiotic use 1

Group A Streptococcal Infections (Pharyngitis, Scarlet Fever)

• 50-75 mg/kg/day divided every 12 hours for 10 days (maximum 1000 mg per dose) 2
• Must complete full 10-day course to prevent acute rheumatic fever 3

Critical Dosing Considerations

Maximum Doses

• Absolute maximum: 4000 mg/day regardless of weight 1, 2, 3
• For a 50 kg child requiring high-dose therapy (90 mg/kg/day = 4500 mg/day), cap at 4000 mg/day 2

Treatment Duration

• Minimum: 48-72 hours beyond symptom resolution 3
• Streptococcal infections: 10 days mandatory to prevent rheumatic fever 3
• Pneumonia: 7-10 days, with recent evidence supporting shorter courses for uncomplicated cases 2, 4, 5

Administration

• Give at the start of meals to minimize gastrointestinal intolerance 3
• Oral suspension must be shaken well before each use 3
• Reconstituted suspension expires after 14 days; refrigeration preferred but not required 3

Common Pitfalls to Avoid

Underdosing in High-Risk Situations

• Do not use 45 mg/kg/day for children <2 years, those in daycare, or those with recent antibiotic exposure—these populations require 90 mg/kg/day 1
• The emergence of resistant S. pneumoniae makes high-dose therapy increasingly necessary 1

Inadequate Duration

• Never stop antibiotics early even if symptoms improve 2
• Always complete 10 days for streptococcal infections to prevent complications 3

Viral Coinfection Considerations

• Research suggests amoxicillin penetration into middle ear fluid is reduced during viral coinfection, potentially requiring higher doses 6
• However, current guidelines do not differentiate dosing based on viral coinfection status 1

Alternative Formulations

When Amoxicillin Alone is Insufficient

• Amoxicillin-clavulanate (Augmentin): Use 90 mg/kg/day of amoxicillin component for β-lactamase-producing organisms (H. influenzae, M. catarrhalis) 1, 2
• Consider for treatment failures or when β-lactamase producers are suspected 1

Penicillin Allergy

• For non-anaphylactic reactions: Second- or third-generation cephalosporins (cefdinir, cefuroxime) 1
• For serious penicillin allergy: Levofloxacin, moxifloxacin, or linezolid 1
• Risk of cross-reactivity with cephalosporins is minimal for non-Type I reactions 1

Evidence Quality Note

The recommendation for high-dose amoxicillin (90 mg/kg/day) is strongly supported by multiple international guidelines including the Infectious Diseases Society of America and American Academy of Pediatrics 1, 2. Research evidence demonstrates that standard dosing (40-45 mg/kg/day) may be inadequate for resistant pathogens, particularly during viral coinfection 6. However, a recent high-quality RCT found no difference in efficacy between lower and higher doses in low-risk populations 4, 7, suggesting that risk stratification is essential when selecting the appropriate dose.