What is the appropriate amoxicillin dose for a 5‑year‑old child weighing 71 lb (≈32 kg)?

Amoxicillin Dosing for a 5-Year-Old Weighing 71 lbs (32 kg)

For most common infections in this child, prescribe amoxicillin 45 mg/kg/day divided into two doses (approximately 720 mg twice daily), but for community-acquired pneumonia or severe infections, use the high-dose regimen of 90 mg/kg/day divided into two doses (approximately 1,440 mg twice daily, maximum 4,000 mg/day). 1

Weight-Based Calculation

• This 5-year-old weighs 32 kg (71 lbs ÷ 2.2 = 32.3 kg). 1
• Standard-dose regimen: 32 kg × 45 mg/kg/day = 1,440 mg/day = 720 mg twice daily (every 12 hours). 1
• High-dose regimen: 32 kg × 90 mg/kg/day = 2,880 mg/day = 1,440 mg twice daily (every 12 hours). 1

Indication-Specific Dosing Algorithm

Community-Acquired Pneumonia (Presumed Bacterial)

• Use high-dose amoxicillin 90 mg/kg/day (1,440 mg twice daily) for 10 days because this child is < 5 years old, which is an independent indication for high-dose therapy regardless of other risk factors. 1
• The high-dose regimen provides adequate coverage for penicillin-resistant Streptococcus pneumoniae (the most common bacterial pathogen) and achieves therapeutic concentrations against organisms with MICs up to 2–4 mg/L. 1
• Clinical improvement should occur within 48–72 hours; if no improvement, reevaluate and consider atypical pathogens (add azithromycin) or treatment failure. 1

Group A Streptococcal Pharyngitis (Strep Throat)

• Use 50–75 mg/kg/day divided into two doses for 10 days, which translates to 800–1,200 mg twice daily for this 32-kg child. 1
• Maximum single dose is 1,000 mg, so prescribe 1,000 mg twice daily for 10 days. 1
• The full 10-day course must be completed to prevent acute rheumatic fever, even though fever typically resolves within 3–4 days. 1

Acute Otitis Media or Acute Bacterial Sinusitis

Standard-dose indications (45 mg/kg/day = 720 mg twice daily):

• Child is ≥ 2 years old AND
• No daycare attendance AND
• No antibiotic use in the past 30 days AND
• Mild-to-moderate illness. 1

High-dose indications (90 mg/kg/day = 1,440 mg twice daily):

• Any one of the following risk factors mandates high-dose therapy:

  • Age < 2 years (this child is 5 years old, so this does not apply)
  • Daycare attendance
  • Recent antibiotic use (within past 30 days)
  • Moderate-to-severe illness
  • Region with > 10% penicillin-resistant S. pneumoniae. 1

• If β-lactamase-producing organisms (H. influenzae, M. catarrhalis) are suspected (e.g., treatment failure after 48–72 hours, incomplete H. influenzae type b vaccination, or concurrent purulent otitis media), switch to amoxicillin-clavulanate 90 mg/kg/day of the amoxicillin component (1,440 mg amoxicillin component twice daily). 1

Uncomplicated Skin/Soft Tissue or Genitourinary Infections

• Use standard-dose amoxicillin 45 mg/kg/day (720 mg twice daily) for mild-to-moderate infections. 2
• Use high-dose 90 mg/kg/day (1,440 mg twice daily) for severe infections. 2

Practical Prescribing

Liquid Suspension Dosing (if using 400 mg/5 mL formulation)

• Standard dose (720 mg): 9 mL twice daily. 1
• High dose (1,440 mg): 18 mL twice daily. 1

Tablet/Capsule Dosing (if child can swallow pills)

• Standard dose: One 875-mg tablet twice daily (slightly higher than calculated 720 mg, but within acceptable range). 2
• High dose: Two 875-mg tablets twice daily (1,750 mg per dose, which exceeds the calculated 1,440 mg but remains below the 2,000-mg maximum single dose). 1

Critical Dosing Limits

• Maximum single dose: 2,000 mg per administration (regardless of weight). 1
• Maximum daily dose: 4,000 mg per day (regardless of weight). 1, 2
• For this 32-kg child on high-dose therapy (2,880 mg/day), the calculated dose is well below the 4,000-mg/day maximum. 1

Treatment Duration

• Pneumonia: 10 days (minimum 48–72 hours beyond symptom resolution). 1
• Strep throat: 10 days (mandatory to prevent rheumatic fever). 1
• Otitis media/sinusitis: Continue for 7 days after symptom resolution, with a minimum total of 10 days. 1
• Skin/soft tissue infections: 7–10 days (depending on severity). 2

Administration Instructions

• Give at the start of a meal to minimize gastrointestinal side effects. 2
• Shake liquid suspension well before each dose; refrigeration is preferable but not required. 2
• Discard any unused suspension after 14 days. 2

Common Pitfalls to Avoid

• Do not use outdated low-dose regimens (e.g., 40 mg/kg/day or 20 mg/kg/day); current guidelines recommend 45–90 mg/kg/day for most infections to address contemporary resistance patterns. 1
• Do not prescribe standard-dose amoxicillin for pneumonia in children < 5 years old—this age group requires high-dose therapy (90 mg/kg/day) regardless of other risk factors. 1
• Do not use plain amoxicillin for treatment failure or suspected β-lactamase producers—switch to amoxicillin-clavulanate (Augmentin) at 90 mg/kg/day of the amoxicillin component. 1
• Do not stop antibiotics early even if symptoms improve—complete the full prescribed course to prevent treatment failure and resistance. 1

Penicillin Allergy Alternatives

Non-Anaphylactic Penicillin Allergy

• Cephalexin 20 mg/kg per dose twice daily (maximum 500 mg per dose) for 10 days. 1
• Cefdinir or cefuroxime are also acceptable second- or third-generation cephalosporins. 1

IgE-Mediated (Type I) Penicillin Allergy

• Clindamycin 7–10 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—use cautiously due to potential macrolide resistance. 1