Amoxicillin 400mg/5mL Dosing for a 75-Pound Child
For a 75-pound (34 kg) child, administer 7.7 mL of amoxicillin 400mg/5mL suspension twice daily for most common respiratory infections, or 15.3 mL twice daily for severe infections or high-resistance areas.
Weight-Based Dose Calculation
A 75-pound child weighs approximately 34 kg, which is the foundation for all pediatric amoxicillin dosing calculations 1.
For mild to moderate respiratory tract infections (including community-acquired pneumonia, acute bacterial sinusitis, or Group A streptococcal pharyngitis), the standard dose is 45 mg/kg/day divided into 2 doses, which equals 765 mg twice daily (≈7.7 mL of 400mg/5mL suspension twice daily) 1, 2.
For severe infections, high pneumococcal resistance areas, children <2 years, daycare attendees, or recent antibiotic use within 30 days, the high-dose regimen is 90 mg/kg/day divided into 2 doses, which equals 1,530 mg twice daily (≈15.3 mL of 400mg/5mL suspension twice daily) 1, 2.
Indication-Specific Dosing Algorithm
Community-Acquired Pneumonia
- Standard dose (no risk factors): 765 mg (7.7 mL) twice daily for 7–10 days 1, 2.
- High-dose (any risk factor present): 1,530 mg (15.3 mL) twice daily for 7–10 days 1, 2.
- Risk factors include: age <2 years, daycare attendance, antibiotic use in past 30 days, >10% local penicillin-resistant S. pneumoniae, or moderate-to-severe illness 1.
Group A Streptococcal Pharyngitis
- Dose: 850–1,275 mg (8.5–12.8 mL) twice daily, not exceeding 1,000 mg per dose, for 10 days 1.
- For this 34 kg child, the practical dose is 1,000 mg (10 mL) twice daily for 10 days 1.
Acute Bacterial Sinusitis
- Age ≥2 years without risk factors: 765 mg (7.7 mL) twice daily for 10 days minimum 1.
- Age <2 years, daycare, or recent antibiotics: 1,360–1,530 mg (13.6–15.3 mL) twice daily for 10 days minimum 1.
Maximum Dose Limits
- The maximum single dose is 2,000 mg regardless of weight 1.
- The maximum daily dose is 4,000 mg (4 grams) per day 1, 2.
- For this 34 kg child, even the high-dose regimen (3,060 mg/day total) remains well below the maximum 1.
Treatment Duration and Monitoring
- Standard duration: 7–10 days for most respiratory infections, with 10 days preferred for pneumonia 1, 2.
- Continue therapy for at least 48–72 hours after complete symptom resolution 1.
- Clinical improvement should occur within 48–72 hours; if no improvement, reevaluate for treatment failure, resistant organisms, or atypical pathogens 1, 2.
When to Use Amoxicillin-Clavulanate Instead
- Switch to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component) when β-lactamase-producing organisms (H. influenzae, M. catarrhalis) are suspected, including treatment failure after initial amoxicillin, incomplete H. influenzae type b vaccination, or concurrent purulent acute otitis media 1.
Critical Dosing Pitfalls to Avoid
- Do not use outdated 40 mg/kg/day dosing—current guidelines recommend 45–90 mg/kg/day for children >3 months to address contemporary resistance patterns 1, 3.
- Do not underdose severe infections—always use 90 mg/kg/day when any high-risk factor is present 1.
- Do not stop antibiotics early—complete the full 10-day course for streptococcal pharyngitis to prevent acute rheumatic fever, even if symptoms resolve in 3–4 days 1.
- Do not exceed 1,000 mg per dose for streptococcal pharyngitis despite weight-based calculations suggesting higher doses 1.