What is the appropriate amoxicillin dosage for a 40 kg child?

Amoxicillin Dosing for a 40 kg Child

For a child weighing exactly 40 kg, use adult dosing regimens rather than pediatric weight-based calculations. 1

Weight-Based Dosing Threshold

• Children weighing more than 40 kg should be dosed as adults according to tuberculosis treatment guidelines that establish this weight threshold as the transition point to adult dosing. 2
• At exactly 40 kg, the child falls at the boundary where pediatric weight-based dosing (which typically applies to children <40 kg) transitions to standard adult fixed-dose regimens. 3

Standard Adult Dosing Regimens

For Mild to Moderate Infections

• 500 mg every 12 hours or 250 mg every 8 hours for ear/nose/throat, skin/skin structure, and genitourinary tract infections. 3

For Severe Infections or Lower Respiratory Tract Infections

• 875 mg every 12 hours or 500 mg every 8 hours for severe infections or any lower respiratory tract infection. 3

Indication-Specific Recommendations

Community-Acquired Pneumonia

• For presumed bacterial pneumonia, use 90 mg/kg/day divided into 2 doses (maximum 4 g/day), which equals approximately 1,800 mg twice daily for a 40 kg child. 2
• This high-dose regimen provides adequate coverage for penicillin-resistant Streptococcus pneumoniae and is recommended by the Infectious Diseases Society of America and Pediatric Infectious Diseases Society. 2

Group A Streptococcal Pharyngitis

• Use 50-75 mg/kg/day divided into 2 doses for 10 days, which translates to approximately 1,000-1,500 mg twice daily for a 40 kg child, with a maximum single dose of 1,000 mg. 2

Acute Otitis Media or Sinusitis (if high-dose needed)

• For children with risk factors (recent antibiotic use, daycare attendance, age <2 years, or high local resistance), use 90 mg/kg/day divided into 2 doses, which equals 1,800 mg twice daily for a 40 kg child. 2

Treatment Duration

• Continue treatment for a minimum of 48-72 hours beyond symptom resolution. 3
• For Group A Streptococcal infections, complete a full 10-day course to prevent acute rheumatic fever. 3
• For pneumonia, treat for 10 days total. 2

When to Use Amoxicillin-Clavulanate Instead

• Switch to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component) if:
  • β-lactamase-producing organisms (H. influenzae, M. catarrhalis) are suspected. 2
  • Treatment failure occurs after 48-72 hours on amoxicillin alone. 4
  • Recent antibiotic exposure within the past 30 days. 4

Clinical Monitoring

• Clinical improvement should be evident within 48-72 hours of initiating therapy. 2
• If no improvement or worsening occurs, reevaluate for resistant organisms, inadequate source control, or alternative diagnoses. 2

Important Caveats

• The maximum daily dose should not exceed 4,000 mg/day regardless of weight. 2
• Amoxicillin should be taken at the start of a meal to minimize gastrointestinal intolerance. 3
• For severe renal impairment (GFR <30 mL/min), dose adjustments are required; do not use the 875 mg dose in patients with GFR <30 mL/min. 3