What is the appropriate amoxicillin suspension dose for a child weighing approximately 45 lb (≈20 kg) with normal renal function and no penicillin allergy?

Amoxicillin Dosing for a 45-Pound Child

For a child weighing 45 pounds (approximately 20.5 kg), the standard amoxicillin suspension dose is 45 mg/kg/day divided into two doses (every 12 hours) for mild to moderate infections, which equals approximately 920 mg per day or 460 mg (approximately 9 mL of 250 mg/5 mL suspension) twice daily. 1, 2

Weight-Based Calculation

• A 45-pound child weighs approximately 20.5 kg (45 ÷ 2.2 = 20.45 kg). 2
• For mild to moderate respiratory tract infections, skin infections, or genitourinary infections, the recommended dose is 45 mg/kg/day divided every 12 hours. 1, 2, 3
• This calculates to: 20.5 kg × 45 mg/kg = 922.5 mg per day, administered as approximately 460 mg twice daily. 1, 2
• Using a 250 mg/5 mL suspension, this equals approximately 9 mL twice daily (every 12 hours). 1

High-Dose Regimen for Severe Infections

If the child has severe infection, recent antibiotic exposure, attends daycare, is under 2 years old, or lives in an area with high pneumococcal resistance (>10%), escalate to 90 mg/kg/day divided twice daily. 1, 2

• The high-dose regimen for this 20.5 kg child would be: 20.5 kg × 90 mg/kg = 1,845 mg per day, administered as approximately 920 mg twice daily. 1, 2
• Using a 250 mg/5 mL suspension, this equals approximately 18 mL twice daily. 1
• This high-dose regimen is specifically indicated for community-acquired pneumonia, severe respiratory infections, or areas with penicillin-resistant Streptococcus pneumoniae. 1, 2

Indication-Specific Dosing

Community-Acquired Pneumonia

• For presumed bacterial pneumonia in children ≥5 years: 90 mg/kg/day in 2 doses (maximum 4 g/day). 1, 2
• For children <5 years with pneumonia: 90 mg/kg/day in 2 doses. 1

Group A Streptococcal Pharyngitis

• Recommended dose: 50-75 mg/kg/day in 2 doses for 10 days, with a maximum single dose of 1,000 mg. 1, 2
• For this 20.5 kg child: approximately 1,025-1,537 mg per day, but capped at 1,000 mg per dose (2,000 mg per day maximum). 1

Acute Otitis Media

• Standard dose: 40-45 mg/kg/day in 2 divided doses for uncomplicated cases. 2
• High-dose: 80-90 mg/kg/day in 2 doses for children <2 years, recent antibiotic use, or severe presentation. 1, 4

Treatment Duration and Monitoring

• Continue therapy for a minimum of 48-72 hours beyond symptom resolution, with most respiratory infections requiring 7-10 days of treatment. 1, 2
• For pneumonia specifically, a 10-day course is recommended. 1, 2
• Clinical improvement should be evident within 48-72 hours; if no improvement occurs, reassess for treatment failure, resistant organisms, or atypical pathogens. 1, 2

Maximum Dosing Limits

• The maximum daily dose should not exceed 4,000 mg per day regardless of weight. 1, 2, 3
• For Group A streptococcal infections, the maximum single dose is 1,000 mg. 1

When to Switch to Amoxicillin-Clavulanate

Consider switching to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate) if:

• The child received antibiotics within the past 30 days. 1, 4
• No clinical improvement after 48-72 hours of amoxicillin therapy. 1, 2
• Suspected β-lactamase-producing organisms (Haemophilus influenzae, Moraxella catarrhalis). 1, 4
• Incomplete Haemophilus influenzae type b vaccination or concurrent purulent otitis media. 1, 4

Common Pitfalls to Avoid

• Verify the suspension concentration (125 mg/5 mL vs. 250 mg/5 mL) before calculating volume to prevent dosing errors. 4
• Do not underdose older or heavier children—research shows that children above 20 kg frequently receive subtherapeutic doses when clinicians hesitate to exceed "adult doses." 5, 6
• For a 20.5 kg child, the high-dose regimen (920 mg twice daily) is below the adult maximum of 1,500 mg per day and is entirely appropriate. 7, 6
• Shake the suspension well before each use and discard any unused portion after 14 days. 3
• Amoxicillin can be given without regard to meals, though administration with food may improve gastrointestinal tolerability. 2