What is the appropriate dosage of Amoxi (amoxicillin) 400mg/5ml for a 37-pound pediatric patient?

Amoxicillin Dosing for a 37-Pound Pediatric Patient

For a 37-pound (16.8 kg) child, the appropriate dose of amoxicillin 400mg/5ml suspension is 6.3 mL twice daily (providing 50 mg/kg/day) for standard infections, or 11.3 mL twice daily (providing 90 mg/kg/day) for high-risk infections or suspected resistant organisms. 1, 2

Weight Conversion and Dose Calculation

• 37 pounds = 16.8 kg
• The 400mg/5ml suspension provides 80 mg/mL concentration 2

Standard-Dose Regimen (For Low-Risk Infections)

For mild to moderate infections without risk factors:

• Dose: 25 mg/kg/dose every 12 hours 2
• For this 16.8 kg child: 25 mg/kg × 16.8 kg = 420 mg per dose
• Volume: 5.25 mL (approximately 5 mL) twice daily 2
• Total daily dose: 50 mg/kg/day (840 mg/day)

This standard regimen is appropriate for children without recent antibiotic exposure, not attending daycare, and in communities with low prevalence of resistant Streptococcus pneumoniae (<10%). 3, 4

High-Dose Regimen (For High-Risk Infections)

For moderate to severe infections or children with risk factors, use high-dose amoxicillin:

• Dose: 45 mg/kg/dose every 12 hours 2
• For this 16.8 kg child: 45 mg/kg × 16.8 kg = 756 mg per dose
• Volume: 9.5 mL twice daily 2
• Total daily dose: 90 mg/kg/day (1,512 mg/day)

Risk Factors Requiring High-Dose Therapy

High-dose amoxicillin (80-90 mg/kg/day) is indicated when any of the following risk factors are present: 3, 1

• Age younger than 2 years 1
• Daycare attendance 3, 1
• Recent antibiotic use within the previous 30 days 3, 1
• Moderate to severe illness at presentation 3
• Geographic area with high prevalence (>10%) of penicillin-resistant S. pneumoniae 3

When to Use Amoxicillin-Clavulanate Instead

Switch to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component with 6.4 mg/kg/day clavulanate) if: 3, 1

• Treatment failure after 48-72 hours on amoxicillin alone 1
• Suspected β-lactamase-producing organisms (H. influenzae or M. catarrhalis) 3
• Incomplete Haemophilus influenzae type b vaccination 1
• Initial presentation with severe illness 1

Treatment Duration and Monitoring

• Continue treatment for minimum 48-72 hours beyond symptom resolution 2
• For Streptococcus pyogenes infections, treat for at least 10 days to prevent acute rheumatic fever 2
• Most respiratory infections require 7-10 days of treatment 3, 5
• Clinical improvement should be evident within 48-72 hours; if not, reassess the patient 1, 5

Critical Dosing Considerations

Common pitfalls to avoid:

• Verify the suspension concentration before dispensing - this patient has 400mg/5ml (80 mg/mL), but other concentrations exist (125mg/5ml, 250mg/5ml) 1, 2
• Underdosing leads to treatment failure and promotes antimicrobial resistance - standard 40 mg/kg/day dosing is inadequate for resistant organisms 6, 4
• Administer at the start of meals to minimize gastrointestinal intolerance 2
• Shake suspension well before each use 2
• Discard unused suspension after 14 days; refrigeration is preferable but not required 2

Evidence Supporting Dosing Recommendations

The high-dose regimen (80-90 mg/kg/day) achieves middle ear fluid and sinus concentrations adequate to overcome penicillin-resistant S. pneumoniae with MICs up to 2-4 mg/L. 1, 6 Research demonstrates that standard 40 mg/kg/day dosing is inadequate, particularly during viral coinfection, which reduces antibiotic penetration into infected tissues. 6 The twice-daily dosing schedule improves adherence compared to three-times-daily regimens while maintaining comparable efficacy. 7, 8

Local prevalence data suggest that while nasopharyngeal carriage of nonsusceptible S. pneumoniae may be high (48% of isolates), the actual probability of infection with highly resistant strains requiring high-dose therapy is lower (3-7%). 4 However, given the consequences of treatment failure, high-dose therapy is warranted when risk factors are present. 3, 1