What is the recommended dosage of Amoxicillin (Amoxycillin) for a pediatric patient?

Amoxicillin Dosing for Pediatric Patients

For most common pediatric infections, amoxicillin should be dosed at 45 mg/kg/day divided into 2 doses (every 12 hours), with higher dosing of 90 mg/kg/day in 2 doses reserved for severe infections, high-resistance areas, or specific risk factors. 1

Standard Dosing Algorithm

Weight-based dosing is essential and should always be used rather than age-based approximations for accurate and safe prescribing. 1, 2

Mild to Moderate Infections

• 45 mg/kg/day divided every 12 hours for uncomplicated respiratory tract infections, skin infections, and genitourinary infections in children ≥3 months old and weighing <40 kg 1
• This provides adequate coverage for most susceptible pathogens including Streptococcus pneumoniae, Haemophilus influenzae (non-β-lactamase producing), and Streptococcus pyogenes 1
• Treatment duration is typically 7-10 days for most respiratory infections 1

High-Dose Regimen (90 mg/kg/day)

Use 90 mg/kg/day divided every 12 hours when any of the following risk factors are present: 1

• Community-acquired pneumonia in areas with >10% penicillin-resistant S. pneumoniae
• Children <2 years old
• Recent antibiotic exposure within the past 30 days
• Daycare attendance
• Severe infections requiring hospitalization
• Incomplete Haemophilus influenzae type b vaccination

Maximum Daily Dose

• Do not exceed 4000 mg/day regardless of weight 1

Indication-Specific Dosing

Community-Acquired Pneumonia

• Mild to moderate (outpatient): 45 mg/kg/day divided every 12 hours 1
• Severe or high-resistance areas: 90 mg/kg/day divided every 12 hours 1
• Treatment duration: 10 days 1
• Clinical improvement should be evident within 48-72 hours; if no improvement occurs, reevaluation is necessary 1

Group A Streptococcal Pharyngitis (Scarlet Fever)

• 50-75 mg/kg/day divided into 2 doses for 10 days 1
• Maximum single dose: 1000 mg 1
• Patients become non-contagious after 24 hours of antibiotic therapy 1

Acute Bacterial Sinusitis

• Children ≥2 years without risk factors: 45 mg/kg/day divided every 12 hours 1
• Children <2 years, in daycare, or with recent antibiotic use: 80-90 mg/kg/day divided every 12 hours 1

When to Use Amoxicillin-Clavulanate Instead

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

• β-lactamase-producing organisms (H. influenzae, M. catarrhalis)
• Treatment failure after 48-72 hours on amoxicillin alone
• Recent antibiotic use within the past 4-6 weeks
• Incomplete H. influenzae type b vaccination with concurrent purulent otitis media

Practical Dosing Examples

Example 1: 3-Month-Old Infant (5.5 kg) with Pneumonia

• Mild to moderate: 45 mg/kg/day = 247.5 mg/day ÷ 2 = 124 mg per dose (approximately 1.25 mL of 250 mg/5 mL suspension twice daily) 1
• Severe or high resistance: 90 mg/kg/day = 495 mg/day ÷ 2 = 247.5 mg per dose (approximately 2.5 mL twice daily) 1

Example 2: 5-Year-Old Child (18 kg) with Strep Throat

• 50-75 mg/kg/day = 900-1350 mg/day ÷ 2 = 450-675 mg per dose 1
• Using 400 mg/5 mL suspension: approximately 5.6-8.4 mL twice daily (not exceeding 1000 mg per dose) 1

Example 3: 8-Year-Old Child (44.5 kg) with Pharyngitis

• 50-75 mg/kg/day = 2225-3337.5 mg/day, but maximum 1000 mg per dose 1
• Administer 1000 mg twice daily for 10 days 1

Critical Monitoring Points

• Expect clinical improvement within 48-72 hours of starting therapy 1
• If no improvement or worsening occurs after 72 hours, reassess diagnosis and consider:
  • Atypical pathogens requiring macrolide addition 1
  • Complications or alternative diagnoses 1
  • Switch to amoxicillin-clavulanate for β-lactamase-producing organisms 1

Common Pitfalls to Avoid

1. Using age-based rather than weight-based dosing leads to under- or overdosing 2
2. Underdosing in high-resistance areas or with risk factors promotes treatment failure and antimicrobial resistance 1
3. Prescribing antibiotics for viral URTIs increases adverse effects without benefit 3
4. Stopping treatment early when symptoms improve before completing the full course 1
5. Not documenting weight, daily dose, number of divided doses, duration, and indication on prescriptions leads to dispensing errors 2

Alternative Treatments for Penicillin Allergy

• Non-anaphylactic reactions: Second- or third-generation cephalosporins (cefdinir, cefuroxime) 1
• Serious penicillin allergy (Type I hypersensitivity): Levofloxacin, moxifloxacin, or linezolid 1

Evidence Quality Note

The dosing recommendations are based on high-quality guidelines from the American Academy of Pediatrics and Infectious Diseases Society of America 1, with supporting evidence from recent randomized controlled trials demonstrating that twice-daily dosing is as effective as three-times-daily dosing for equivalent total daily doses 4, 5, 6. The CAP-IT trial (2021) demonstrated that lower-dose amoxicillin (35-50 mg/kg/day) was noninferior to higher dose (70-90 mg/kg/day) in unselected children with CAP, though disease severity and prior antibiotic exposure require consideration 6.