What is the appropriate weight‑based amoxicillin dosing regimen and treatment duration for children with acute bacterial infections such as otitis media, sinusitis, streptococcal pharyngitis, or pneumonia?

Amoxicillin Dosing in Pediatric Patients

For most acute bacterial infections in children ≥3 months old, prescribe amoxicillin 45 mg/kg/day divided into 2 doses for mild-to-moderate infections, or 90 mg/kg/day divided into 2 doses for severe infections, high-resistance areas, or children with specific risk factors (maximum 4 g/day). 1

Standard-Dose Regimen (45 mg/kg/day)

Use standard-dose amoxicillin (45 mg/kg/day in 2 divided doses) for:

• Uncomplicated respiratory tract infections in children ≥2 years without recent antibiotic exposure 2, 1
• Community-acquired pneumonia (mild-to-moderate) in outpatient settings 1
• Acute bacterial sinusitis in children ≥2 years who do not attend daycare and have not received antibiotics in the past 4 weeks 2
• Skin and genitourinary infections in children ≥3 months and <40 kg 1

This dosing provides adequate coverage against susceptible Streptococcus pneumoniae, non-β-lactamase-producing Haemophilus influenzae, and Streptococcus pyogenes. 1

High-Dose Regimen (80–90 mg/kg/day)

Prescribe high-dose amoxicillin (80–90 mg/kg/day in 2 divided doses, maximum 4 g/day) when ANY of the following risk factors are present:

• Age <2 years 2, 1
• Daycare attendance 2, 1
• Recent antibiotic use (within past 30 days) 2, 1
• Geographic areas with >10% penicillin-resistant S. pneumoniae 2, 1
• Moderate-to-severe illness at presentation 2
• Incomplete Haemophilus influenzae type b vaccination 1

High-dose therapy achieves sinus and middle-ear fluid concentrations adequate to overcome penicillin-resistant S. pneumoniae (MIC up to 2–4 mg/L). 2, 3

Indication-Specific Dosing

Group A Streptococcal Pharyngitis

• 50–75 mg/kg/day in 2 divided doses for 10 days (maximum 1,000 mg per dose) 1
• Patients become non-contagious after 24 hours of therapy 1
• Therapy may be initiated up to 9 days after symptom onset and still prevent acute rheumatic fever 1

Acute Otitis Media

• Standard dose (45 mg/kg/day): For children ≥2 years without risk factors 4
• High dose (80–90 mg/kg/day): For children <2 years, recent antibiotic exposure, or severe presentation 1, 3
• Treatment duration: 10 days for children <6 years 3

Community-Acquired Pneumonia

• Mild-to-moderate: 45 mg/kg/day in 2 doses 1
• Severe or high-resistance areas: 90 mg/kg/day in 2 doses 1
• Treatment duration: 10 days 1

Acute Bacterial Sinusitis

• Standard dose (45 mg/kg/day): Children ≥2 years without risk factors 2
• High dose (80–90 mg/kg/day): Children <2 years, daycare attendees, or recent antibiotic use 2
• Treatment duration: Continue for 7 days after symptom resolution (minimum 10 days total) 2

When to Use Amoxicillin-Clavulanate Instead

Switch from amoxicillin to amoxicillin-clavulanate (90 mg/kg/day of amoxicillin component + 6.4 mg/kg/day clavulanate in 2 doses) when:

• Treatment failure after 48–72 hours on amoxicillin alone 1, 3
• Recent antibiotic exposure within 4–6 weeks 4, 3
• Suspected β-lactamase-producing organisms (H. influenzae, M. catarrhalis) 2, 1
• Incomplete H. influenzae type b vaccination (<3 doses) 3
• Concurrent purulent acute otitis media with pneumonia 1

The high-dose amoxicillin-clavulanate formulation (14:1 ratio) provides adequate clavulanate levels to inhibit all β-lactamase-producing H. influenzae and M. catarrhalis while minimizing diarrhea compared to other ratios. 2, 3

Treatment Duration by Indication

• Group A streptococcal pharyngitis: 10 days 1
• Acute otitis media: 10 days (children <6 years); 5–7 days may be considered in older children 4, 3
• Community-acquired pneumonia: 10 days 1
• Acute bacterial sinusitis: 7 days after symptom resolution (minimum 10 days) 2
• Most respiratory infections: 7–10 days 1

Monitoring and Expected Response

• Clinical improvement should occur within 48–72 hours of initiating therapy 1, 3
• Fever typically resolves within 24–48 hours for pneumococcal infections, though cough may persist 1
• If no improvement or worsening after 48–72 hours: Reassess diagnosis, consider atypical pathogens, switch to amoxicillin-clavulanate, or add a macrolide 1, 3

Maximum Dosing Limits

• Maximum daily dose: 4,000 mg/day (4 g/day) regardless of weight 1
• Maximum single dose: 2,000 mg per dose 2, 3
• For children ≥40 kg: Dose as adults using standard adult formulations 1

Penicillin-Allergic Patients

• Non-anaphylactic reactions: Second- or third-generation cephalosporins (cefdinir, cefuroxime, cephalexin) are safe alternatives; cross-reactivity risk is negligible 2, 1
• Type I (IgE-mediated) reactions: Use clindamycin (10–20 mg/kg/day in 3 doses) or azithromycin (12 mg/kg once daily for 5 days), though these have inferior efficacy 1, 4

Critical Pitfalls to Avoid

• Do NOT underdose older or heavier children: Prescribers often give subtherapeutic doses to children >20 kg, leading to treatment failure and resistance 5
• Do NOT prescribe antibiotics for viral URTIs: Approximately 70% of pediatric sore throats are viral and require no antibiotics 1
• Do NOT use amoxicillin alone for β-lactamase producers: Use amoxicillin-clavulanate when H. influenzae or M. catarrhalis are suspected 2, 1
• Verify suspension concentration before dispensing: Confusion between 125/31 and 250/62 formulations causes dosing errors 3
• Always document on prescription: Daily dose, number of divided doses, duration, indication, and child's weight 6

Age-Specific Considerations

• Infants <3 months: Amoxicillin safety data are limited; prefer intravenous regimens (ampicillin + gentamicin or cefotaxime) for serious bacterial infections 3
• Children ≥3 months: Amoxicillin is safe and effective for indicated bacterial infections 1, 3
• Children unable to tolerate oral medication: Single dose of ceftriaxone 50 mg/kg IV/IM, then switch to oral therapy after 24 hours if improved 2