What is the recommended dose of amoxicillin for pediatric patients?

Amoxicillin Dosing for Pediatric Patients

For most pediatric respiratory and common bacterial infections, prescribe amoxicillin 45 mg/kg/day divided every 12 hours for mild-to-moderate cases, or 90 mg/kg/day divided every 12 hours for severe infections or areas with high pneumococcal resistance, with an absolute maximum of 4000 mg/day regardless of weight. 1, 2

Standard Dosing Algorithm by Severity and Age

For Children ≥3 Months and <40 kg:

Mild-to-Moderate Infections (uncomplicated respiratory tract infections, skin infections, genitourinary infections):

• 45 mg/kg/day divided every 12 hours (preferred for adherence) 1, 2, 3
• Alternative: 40 mg/kg/day divided every 8 hours 3
• This provides adequate coverage for Streptococcus pneumoniae, non-β-lactamase-producing Haemophilus influenzae, and Streptococcus pyogenes 2

Severe Infections or High-Resistance Areas:

• 90 mg/kg/day divided every 12 hours 1, 2
• Alternative: 80 mg/kg/day divided every 8 hours 3
• Use this higher dose for: community-acquired pneumonia in areas with >10% penicillin-resistant S. pneumoniae, children <2 years old, recent antibiotic exposure within 30 days, daycare attendance, or hospitalized patients 2

For Children ≥40 kg:

• Mild-to-moderate infections: 500 mg every 12 hours or 250 mg every 8 hours 2, 3
• Severe infections: 875 mg every 12 hours or 500 mg every 8 hours 2, 3
• Absolute maximum: 4000 mg/day regardless of weight 2, 3

For Infants <3 Months (12 weeks):

• Maximum 30 mg/kg/day divided every 12 hours due to immature renal function 3
• Treatment duration: minimum 48-72 hours beyond symptom resolution 3

Indication-Specific Dosing

Group A Streptococcal Pharyngitis (Strep Throat/Scarlet Fever):

• 50-75 mg/kg/day divided into 2 doses for 10 days 1, 2
• Maximum 1000 mg per dose 1
• Mandatory 10-day duration to prevent rheumatic fever 2, 3
• Patients become non-contagious after 24 hours of therapy 2

Community-Acquired Pneumonia:

• Outpatient, mild-to-moderate: 45 mg/kg/day divided every 12 hours 1, 2
• Severe or high-resistance: 90 mg/kg/day divided every 12 hours 1, 2
• Treatment duration: 10 days 1, 2

Acute Bacterial Sinusitis:

• Children ≥2 years without risk factors: 45 mg/kg/day divided every 12 hours 2
• Children <2 years, in daycare, or recent antibiotic use: 80-90 mg/kg/day divided every 12 hours 2

Critical Dosing Considerations and Common Pitfalls

Weight-Based Dosing Disparity: Research demonstrates that larger children frequently receive inadequate doses when clinicians cap amoxicillin at "adult maximum doses" prematurely—children >60 kg often receive <40 mg/kg/day, which is subtherapeutic for resistant organisms 4. Always calculate the weight-based dose first and only apply the 4000 mg/day maximum if the calculated dose exceeds it. 2, 4

Twice-Daily vs. Three-Times-Daily Dosing: Twice-daily dosing (every 12 hours) significantly improves adherence compared to three-times-daily regimens and is the preferred approach 2. Research shows that 25 mg/kg twice daily provides adequate pharmacokinetics for most infections, though 30-40 mg/kg twice daily may be needed for higher MIC targets 5.

Viral Co-Infection Impact: Middle ear fluid penetration of amoxicillin is significantly reduced in children with concurrent viral infections (geometric mean 2.7 mcg/mL with viral infection vs. 5.7 mcg/mL with bacterial-only infection), supporting the use of higher doses (75-90 mg/kg/day) in these scenarios 6.

Renal Impairment Adjustments

For patients with severe renal impairment 3:

• GFR 10-30 mL/min: 500 mg or 250 mg every 12 hours
• GFR <10 mL/min: 500 mg or 250 mg every 24 hours
• Hemodialysis: 500 mg or 250 mg every 24 hours, with additional dose during and at end of dialysis
• Do NOT use 875 mg dose if GFR <30 mL/min 3

Treatment Duration

• Most respiratory infections: 7-10 days 1, 2
• Pneumonia specifically: 10 days 1, 2
• Group A Streptococcal infections: 10 days (mandatory to prevent rheumatic fever) 2, 3
• Minimum for all infections: 48-72 hours beyond symptom resolution 3

Monitoring and Follow-Up

Clinical improvement should occur within 48-72 hours of starting treatment 1, 2. If no improvement by 72 hours, reassess the diagnosis and consider:

• Alternative pathogens (atypical organisms requiring macrolides) 1
• β-lactamase-producing organisms requiring amoxicillin-clavulanate 2
• Non-infectious etiology 2

Complete the full prescribed course even if symptoms improve earlier 1, 2.

Prescription Writing Best Practices

Every amoxicillin prescription should include 2:

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

When to Use Amoxicillin-Clavulanate Instead

Switch to amoxicillin-clavulanate (Augmentin) for β-lactamase-producing organisms 2:

• Standard dose: 45 mg/kg/day of amoxicillin component divided every 12 hours 1
• High dose: 90 mg/kg/day of amoxicillin component divided every 12 hours 1, 7
• Indications: H. influenzae, M. catarrhalis, recent antibiotic exposure within 4-6 weeks, or treatment failure on amoxicillin alone 1, 2

Common Adverse Effects

• Gastrointestinal disturbances (diarrhea, nausea, vomiting) are most common 1, 2
• Rash and hypersensitivity reactions may occur; monitor throughout treatment 2

Alternative Antibiotics for Penicillin Allergy

• Non-anaphylactic allergy: Second- or third-generation cephalosporins (cefdinir, cefuroxime) 2
• Serious/Type I allergy: Levofloxacin, moxifloxacin, or linezolid 2