Amoxicillin Dosing for a 15-Year-Old with Community-Acquired Pneumonia
For a 15-year-old with community-acquired pneumonia, prescribe oral amoxicillin 90 mg/kg/day divided into 2 doses (maximum 4 g/day) for outpatient treatment, or intravenous ampicillin 150-200 mg/kg/day every 6 hours if hospitalization is required. 1, 2
Outpatient Management
- Amoxicillin 90 mg/kg/day in 2 divided doses is the definitive first-line treatment for presumed bacterial pneumonia in this age group 1, 2
- The maximum daily dose is 4000 mg (4 g) per day 1, 3
- This high-dose regimen (90 mg/kg/day rather than 45 mg/kg/day) is essential to overcome pneumococcal resistance, and underdosing is a common and dangerous error 2
- Consider adding azithromycin (10 mg/kg on day 1, then 5 mg/kg/day once daily on days 2-5) if atypical pathogens like Mycoplasma pneumoniae or Chlamydophila pneumoniae are suspected based on clinical presentation 1, 2
Treatment Duration
- Standard treatment duration is 7-10 days for most respiratory infections, with pneumonia specifically requiring 10 days 3
- Recent evidence suggests that shorter courses (3-5 days) may be as effective as longer courses (7-10 days) for uncomplicated CAP, though clinical improvement should be assessed at 48-72 hours 4, 5
Inpatient Management
If the patient requires hospitalization due to severity or treatment failure:
- Intravenous ampicillin 150-200 mg/kg/day every 6 hours is the preferred treatment for fully immunized, low-risk patients 6, 2
- Alternative: Ceftriaxone 50-100 mg/kg/day every 12-24 hours or cefotaxime 150 mg/kg/day every 8 hours 6, 1
- Add vancomycin 40-60 mg/kg/day every 6-8 hours or clindamycin 40 mg/kg/day every 6-8 hours if MRSA is suspected (severe presentation, necrotizing infiltrates, empyema, or recent influenza) 6, 2
Critical Considerations for Adolescents
- At 15 years old, this patient falls into the "children 5-16 years" category for dosing purposes 6
- For Streptococcus pneumoniae (the most common bacterial pathogen), amoxicillin 90 mg/kg/day in 2 doses provides optimal coverage 6, 1
- For Group A Streptococcus, amoxicillin 50-75 mg/kg/day in 2 doses is adequate 6
- Twice-daily dosing improves adherence compared to three-times-daily regimens 3
Monitoring and Reassessment
- Clinical improvement should occur within 48-72 hours of starting appropriate therapy 1, 3
- If no improvement is seen within this timeframe, reassess for complications (empyema, parapneumonic effusion), alternative diagnoses, or resistant organisms 1, 2
- Obtain blood cultures and consider pleural fluid sampling if effusion is present before changing antibiotics 2
Penicillin Allergy Alternatives
- For non-severe allergic reactions: Consider oral cephalosporins (cefpodoxime, cefprozil, or cefuroxime) under medical supervision 1, 2
- For severe allergic reactions (anaphylaxis): Levofloxacin 8-10 mg/kg/day once daily (maximum 750 mg/day) or linezolid 20 mg/kg/day in 2 doses for children ≥12 years 6, 2
Common Pitfalls to Avoid
- Do not underdose amoxicillin at 40-45 mg/kg/day instead of the recommended 90 mg/kg/day 2
- Do not use macrolides as first-line monotherapy for presumed bacterial pneumonia; they should only be added to beta-lactams when atypical pathogens are suspected 2
- Do not fail to consider MRSA in patients with severe pneumonia, especially with necrotizing infiltrates, empyema, or recent influenza infection 2