What is the weight-based dose of amoxicillin for a patient with normal renal function and no known allergy to penicillins (PCN)?

Weight-Based Dosing for Amoxicillin

For adults and pediatric patients ≥3 months old weighing ≥40 kg, amoxicillin dosing is 500 mg every 12 hours or 250 mg every 8 hours for mild/moderate infections, and 875 mg every 12 hours or 500 mg every 8 hours for severe infections. 1

For pediatric patients ≥3 months old weighing <40 kg, the standard dose is 25 mg/kg/day divided every 12 hours or 20 mg/kg/day divided every 8 hours for mild/moderate infections, and 45 mg/kg/day divided every 12 hours or 40 mg/kg/day divided every 8 hours for severe infections. 1

Pediatric Dosing (<40 kg)

Standard Dosing by Severity

• Mild to moderate infections (ear/nose/throat, skin/skin structure, genitourinary): 25 mg/kg/day divided every 12 hours OR 20 mg/kg/day divided every 8 hours 1
• Severe infections (all sites) and all lower respiratory tract infections: 45 mg/kg/day divided every 12 hours OR 40 mg/kg/day divided every 8 hours 1

Special Pediatric Populations

• Infants <3 months (12 weeks): Maximum 30 mg/kg/day divided every 12 hours due to incompletely developed renal function 1
• Streptococcal pharyngitis: 50 mg/kg once daily (maximum 1,000 mg) OR 25 mg/kg twice daily (maximum 500 mg) for 10 days 2
• Infective endocarditis (penicillin-susceptible streptococci): 300 mg/kg/day IV in 4-6 equally divided doses for standard 4-week treatment 2

Adult Dosing (≥40 kg)

Standard Oral Dosing

• Mild/moderate infections: 500 mg every 12 hours OR 250 mg every 8 hours 1
• Severe infections or lower respiratory tract: 875 mg every 12 hours OR 500 mg every 8 hours 1
• H. pylori triple therapy: 1 gram twice daily for 14 days (with clarithromycin and lansoprazole) 1

Intravenous Dosing for Serious Infections

• Infective endocarditis (penicillin-susceptible streptococci): 100-200 mg/kg/day IV in 4-6 doses for 4 weeks 2
• Penicillin-resistant streptococci (MIC 0.25-2 mg/L): 200 mg/kg/day IV in 4-6 doses for 4 weeks 2

Renal Impairment Adjustments

Patients with severe renal impairment require dose reduction, and the 875 mg dose should NOT be used if GFR <30 mL/min. 1

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours (depending on severity) 1
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours 1
• Hemodialysis: 500 mg or 250 mg every 24 hours, with additional dose during and at end of dialysis 1

Critical Dosing Considerations

Maximum Dose Concerns in Obesity

• In children with obesity, weight-based dosing at 80-90 mg/kg/day can exceed standard adult maximum doses of 1,500 mg/day 3
• Primary care physicians often prescribe significantly lower-than-recommended doses in older and heavier children 3
• When calculated pediatric doses exceed adult maximum doses, clinical judgment is required—some experts cap at adult dose while others maintain weight-based dosing 3

Duration of Therapy

• Minimum treatment: 48-72 hours beyond symptom resolution or bacterial eradication 1
• Streptococcus pyogenes infections: Minimum 10 days to prevent acute rheumatic fever 1
• Some infections may require several weeks of therapy 1

Administration Guidelines

Optimal Absorption

• Administer at the start of a meal to minimize gastrointestinal intolerance 1

Oral Suspension Preparation

• Shake bottle until powder flows freely, add 1/3 of required water, shake vigorously, add remaining water, shake again 1
• Shake well before each use 1
• Refrigeration preferable but not required; discard unused portion after 14 days 1
• Can be mixed with formula, milk, fruit juice, water, or cold drinks and taken immediately 1

Common Pitfalls to Avoid

• Underdosing in children: Age-based dosing without weight consideration leads to underdosing in 54.6% of children (pre-2014 guidance) 4
• Failure to adjust for renal impairment: Severe renal dysfunction requires significant dose reduction 1
• Using 875 mg dose in renal impairment: This dose is contraindicated when GFR <30 mL/min 1
• Inadequate treatment duration for streptococcal infections: Must complete minimum 10 days to prevent rheumatic fever 1
• Not considering infection severity: Lower respiratory tract infections and severe infections require higher doses (45 mg/kg/day vs 25 mg/kg/day in children) 1