What is the first‑line antibiotic regimen (including dose and duration) for an otherwise healthy outpatient child with community‑acquired pneumonia, and what alternatives are recommended for penicillin allergy or suspected atypical pathogens?

First-Line Antibiotic Treatment for Pediatric Community-Acquired Pneumonia

Amoxicillin 90 mg/kg/day divided into 2 doses (maximum 4 g/day) is the definitive first-line antibiotic for otherwise healthy outpatient children with community-acquired pneumonia, regardless of age. 1, 2, 3

Outpatient Treatment Algorithm

Children < 5 Years Old (Preschool)

Presumed bacterial pneumonia:

• Amoxicillin 90 mg/kg/day divided into 2 doses for 5–7 days 1, 2, 4
• This high dose is essential to overcome pneumococcal resistance; underdosing with 40–45 mg/kg/day is a dangerous and common error 2
• Alternative if not fully immunized against H. influenzae type b or S. pneumoniae: amoxicillin-clavulanate (amoxicillin component 90 mg/kg/day in 2 doses) 1, 4

Presumed atypical pneumonia (rare in this age group):

• Azithromycin 10 mg/kg on day 1, then 5 mg/kg/day once daily on days 2–5 1, 5
• Alternatives: clarithromycin 15 mg/kg/day in 2 doses for 7–14 days or erythromycin 40 mg/kg/day in 4 doses 1

Children ≥ 5 Years Old (School-Age)

Presumed bacterial pneumonia:

• Amoxicillin 90 mg/kg/day in 2 doses (maximum 4 g/day) for 5–7 days 1, 2, 3
• Add azithromycin (10 mg/kg day 1, then 5 mg/kg/day days 2–5; maximum 500 mg day 1, then 250 mg days 2–5) if clinical features do not clearly distinguish bacterial from atypical pneumonia 1, 2, 3
• Atypical pathogens (Mycoplasma pneumoniae, Chlamydophila pneumoniae) are more common in this age group 5, 6

Presumed atypical pneumonia alone:

• Azithromycin monotherapy using the same dosing as above 1, 3, 5
• Alternatives: clarithromycin 15 mg/kg/day in 2 doses (maximum 1 g/day) or doxycycline for children > 7 years 1

Treatment Duration

5 days of amoxicillin is as effective as 10 days for uncomplicated community-acquired pneumonia in outpatient children, with moderate-quality evidence supporting this shorter course 7, 4, 8

Penicillin Allergy Management

Non-Severe Allergic Reactions (e.g., rash without anaphylaxis)

• Oral cephalosporins under medical supervision: cefpodoxime, cefprozil, or cefuroxime 2, 6
• Cross-reactivity risk between penicillins and cephalosporins is low (1–3%) for non-anaphylactic reactions 2
• Azithromycin is a safe alternative that avoids all beta-lactams: 10 mg/kg day 1 (max 500 mg), then 5 mg/kg/day days 2–5 (max 250 mg/day) 2, 3

Severe Allergic Reactions (anaphylaxis, angioedema)

• Levofloxacin is the preferred alternative 2, 6
  • Children 6 months to 5 years: 16–20 mg/kg/day divided into 2 doses
  • Children 5–16 years: 8–10 mg/kg once daily (maximum 750 mg/day) 2
• Alternative: linezolid 30 mg/kg/day divided into 3 doses for children < 12 years, or 20 mg/kg/day divided into 2 doses for children ≥ 12 years 2

Inpatient Treatment (Hospitalized Children)

Fully Immunized, Low-Risk Children

• Ampicillin 150–200 mg/kg/day IV every 6 hours OR penicillin G 200,000–250,000 U/kg/day IV every 4–6 hours 1, 2, 3
• Alternative: ceftriaxone 50–100 mg/kg/day IV once daily or every 12–24 hours 1, 2

Not Fully Immunized or High-Risk Children

• Ceftriaxone 50–100 mg/kg/day IV OR cefotaxime 150 mg/kg/day IV every 8 hours 1, 2, 3
• This regimen covers penicillin-resistant S. pneumoniae, β-lactamase-producing H. influenzae, and other resistant organisms 2

Suspected MRSA (severe pneumonia, necrotizing infiltrates, empyema, recent influenza)

• Add vancomycin 40–60 mg/kg/day IV every 6–8 hours OR clindamycin 40 mg/kg/day IV every 6 hours to the beta-lactam regimen 1, 2, 3
• Failure to consider MRSA in severe presentations is a critical pitfall 2

Atypical Pneumonia (Hospitalized)

• Azithromycin 10 mg/kg IV on days 1 and 2, then transition to oral therapy 1, 2
• Alternative: erythromycin lactobionate 20 mg/kg/day IV every 6 hours 2

Clinical Monitoring and Treatment Failure

Children on adequate therapy should demonstrate clinical improvement within 48–72 hours (reduced fever, improved respiratory effort, better oral intake) 1, 2, 3, 9

If no improvement or deterioration occurs within 48–72 hours:

• Obtain blood cultures and consider pleural fluid sampling if effusion is present 2
• Reassess for complications: parapneumonic effusion, empyema, necrotizing pneumonia, lung abscess 1, 2
• Consider resistant organisms (MRSA, penicillin-resistant S. pneumoniae) or alternative diagnoses 2, 3
• Escalate to intravenous antibiotics if outpatient, or broaden coverage if already hospitalized 2

Critical Pitfalls to Avoid

• Never use macrolides as first-line monotherapy for presumed bacterial pneumonia in children < 5 years; they lack reliable activity against S. pneumoniae 2, 3
• Never underdose amoxicillin; 90 mg/kg/day (not 40–45 mg/kg/day) is required to overcome resistance 2
• Never use cefixime or cefdinir as first-line empiric therapy; they have inadequate pneumococcal coverage compared to high-dose amoxicillin 2
• Never delay adding vancomycin or clindamycin in severe pneumonia with necrotizing features or empyema, as MRSA is a life-threatening possibility 2
• Never continue inadequate therapy beyond 48–72 hours without reassessment; prompt escalation prevents treatment failure 1, 2