What is the appropriate dosage of amoxicillin (amoxicillin) liquid for a 40 kg child?

Amoxicillin Liquid Prescription for a 40 kg Child

For a 40 kg child, prescribe amoxicillin oral suspension 500 mg (10 mL of 250 mg/5 mL suspension) every 12 hours for mild to moderate infections, or 875 mg (17.5 mL of 250 mg/5 mL suspension) every 12 hours for severe infections or high pneumococcal resistance areas. 1

Weight-Based Dosing Threshold

• Children weighing 40 kg or more should receive adult dosing rather than pediatric weight-based calculations 2, 1
• The FDA label specifically states that for children ≥40 kg with mild to moderate infections: 500 mg every 12 hours or 250 mg every 8 hours 1
• For severe infections or lower respiratory tract infections in children ≥40 kg: 875 mg every 12 hours or 500 mg every 8 hours 1

Indication-Specific Dosing

Mild to Moderate Respiratory Infections

• Standard dose: 500 mg every 12 hours (equivalent to 25 mg/kg/day for a 40 kg child) 2, 1
• This provides adequate coverage for typical pathogens including Streptococcus pneumoniae and Haemophilus influenzae 3

Severe Infections or High Resistance Areas

• High dose: 875 mg every 12 hours (equivalent to approximately 45 mg/kg/day) 3, 2
• The Infectious Diseases Society of America recommends this higher dosing for severe respiratory infections or areas with high pneumococcal resistance 3
• Maximum daily dose should not exceed 4000 mg (4 g) per day 3, 2

Group A Streptococcal Infections (Strep Throat/Scarlet Fever)

• Dose: 50-75 mg/kg/day divided into 2 doses for 10 days, not exceeding 1000 mg per dose 3, 2
• For a 40 kg child, this translates to 1000 mg (20 mL of 250 mg/5 mL) every 12 hours for 10 days 3
• The 10-day duration is mandatory to prevent rheumatic fever 2

Sample Prescription Format

Every prescription must include: 2

• Total daily dose in mg/kg/day
• Number of divided doses per day
• Duration of therapy
• Indication for prescription
• Child's weight

Example Prescription for Mild Respiratory Infection:

Amoxicillin 250 mg/5 mL oral suspension
Dispense: 200 mL
Sig: Give 10 mL (500 mg) by mouth every 12 hours for 10 days
Indication: Community-acquired pneumonia
Patient weight: 40 kg
Total daily dose: 25 mg/kg/day

Example Prescription for Severe Infection:

Amoxicillin 250 mg/5 mL oral suspension
Dispense: 350 mL
Sig: Give 17.5 mL (875 mg) by mouth every 12 hours for 10 days
Indication: Severe pneumonia
Patient weight: 40 kg
Total daily dose: 45 mg/kg/day

Treatment Duration

• Standard duration: 7-10 days for most respiratory infections 3, 2
• Pneumonia specifically requires 10 days of treatment 3
• Group A Streptococcal infections require 10 days to prevent rheumatic fever 2
• Treatment should continue for a minimum of 48-72 hours beyond symptom resolution 1

Administration Instructions

• Take at the start of a meal to minimize gastrointestinal intolerance 1
• Shake suspension well before each use 1
• Refrigeration is preferable but not required 1
• Discard any unused suspension after 14 days 1

Monitoring and Follow-Up

• Clinical improvement should occur within 48-72 hours of starting treatment 3, 2
• If no improvement by 72 hours, reassess diagnosis and consider alternative antibiotics 2
• Complete the full prescribed course even if symptoms improve 3

Common Adverse Effects

• Gastrointestinal disturbances (diarrhea, nausea, vomiting) are most common 4, 2
• Rash, urticaria, and hypersensitivity reactions may occur 4, 2
• Twice-daily dosing improves adherence and reduces diarrhea compared to three-times-daily regimens 2

Critical Pitfalls to Avoid

• Do not use 875 mg tablets in patients with severe renal impairment (GFR <30 mL/min) 1
• Amoxicillin alone is ineffective against MRSA - consider alternative antibiotics if suspected 2
• Avoid prescribing age-based dosing instead of weight-based dosing, as this leads to dosing errors 5
• The older recommendation of 40 mg/kg/day is inadequate for resistant Streptococcus pneumoniae, particularly during viral coinfection 6