What is the appropriate amoxicillin dosage for a 15.8 kg pediatric patient without renal impairment or penicillin allergy?

Amoxicillin Dosing for 15.8 kg Pediatric Patient

For a 15.8 kg pediatric patient without renal impairment or penicillin allergy, amoxicillin should be dosed at 45 mg/kg/day divided every 12 hours (approximately 355 mg per dose twice daily) for severe infections or lower respiratory tract infections, or 25 mg/kg/day divided every 12 hours (approximately 198 mg per dose twice daily) for mild to moderate infections. 1

Weight-Based Dosing Framework

The FDA-approved dosing for pediatric patients weighing less than 40 kg follows a clear severity-based algorithm 1:

Mild to Moderate Infections

• Ear/nose/throat, skin/skin structure, or genitourinary infections: 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 1
• For 15.8 kg patient: This translates to 395 mg total daily (approximately 198 mg per dose twice daily or 132 mg per dose three times daily) 2, 1

Severe Infections or Lower Respiratory Tract Infections

• All lower respiratory tract infections (regardless of severity) and severe infections of other sites: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1
• For 15.8 kg patient: This translates to 711 mg total daily (approximately 355 mg per dose twice daily or 237 mg per dose three times daily) 2, 1

Practical Dosing Calculations

For this specific 15.8 kg patient 2, 3:

Mild to moderate infections:

• Twice-daily dosing: 198 mg per dose (preferred for adherence) 3
• Three-times-daily dosing: 132 mg per dose 1

Severe infections or pneumonia:

• Twice-daily dosing: 355 mg per dose (preferred for adherence) 3
• Three-times-daily dosing: 237 mg per dose 1

Clinical Context Determines Dosing Intensity

The 45 mg/kg/day regimen is specifically indicated for 2, 3:

• Community-acquired pneumonia 4
• Acute otitis media with recent antibiotic exposure or treatment failure 2
• Settings with high prevalence of penicillin-resistant Streptococcus pneumoniae 2
• Any severe infection requiring hospitalization 2

The 25 mg/kg/day regimen is appropriate for 3:

• Uncomplicated acute otitis media 3
• Mild skin and soft tissue infections 1
• Uncomplicated urinary tract infections 3

Group A Streptococcal Infections

For pharyngitis or other Group A Streptococcal infections, use 50-75 mg/kg/day divided into 2 doses for 10 days, not exceeding 1000 mg per dose 4, 3:

• For 15.8 kg patient: 395-593 mg per dose twice daily 3
• Mandatory 10-day duration to prevent rheumatic fever 3, 1

Treatment Duration

Standard durations by indication 3, 1:

• Most respiratory infections: 7-10 days 3
• Pneumonia: 10 days 3
• Group A Streptococcal infections: 10 days (mandatory) 3, 1
• All infections: Continue for minimum 48-72 hours beyond symptom resolution 1

Administration Guidance

• Take at the start of meals to minimize gastrointestinal intolerance 1
• Twice-daily dosing improves adherence compared to three-times-daily regimens and is the preferred approach 3
• Suspension can be mixed with formula, milk, fruit juice, water, or cold drinks and taken immediately 1
• Shake suspension well before each use 1

Critical Dosing Principles

Always use weight-based calculations for children under 40 kg—never use adult fixed doses 2, 5:

• Patient weight in kilograms must be documented on all prescriptions to prevent dosing errors 2
• Do not round to convenient tablet strengths without ensuring the dose falls within the appropriate mg/kg range 2

Common Pitfalls to Avoid

• Do not assume mild dosing for all infections: Lower respiratory tract infections always require the higher 45 mg/kg/day dose regardless of apparent severity 1
• Do not use adult dosing: This 15.8 kg patient is well below the 40 kg threshold and requires pediatric weight-based calculations 2, 5
• Do not prescribe less than 10 days for streptococcal pharyngitis: Shorter courses increase rheumatic fever risk 3, 1
• Reassess if no improvement by 72 hours: Consider alternative diagnosis or resistant organisms 3

Safety Considerations

Renal toxicity with amoxicillin is extremely rare (0.03% incidence) and does not appear dose-related even with massive overdoses 6. No renal dose adjustment is needed for this patient without renal impairment 1. The maximum daily dose is 4000 mg, which this patient will not approach 3.