What is the recommended oral dose of amoxicillin (po tablet) for a 15-year-old patient with pneumonia?

Amoxicillin Dosing for 15-Year-Old with Pneumonia

For a 15-year-old with community-acquired pneumonia, prescribe oral amoxicillin 90 mg/kg/day divided into 2 doses, with a maximum of 4 grams per day (e.g., one 2000-mg tablet twice daily for adolescents who have reached adult weight). 1

Guideline-Based Dosing Algorithm

Age-Appropriate Dosing Category

• A 15-year-old falls into the ≥5 years old category where high-dose amoxicillin is the first-line treatment for presumed bacterial pneumonia 1
• The recommended dose is 90 mg/kg/day divided into 2 doses with a maximum of 4000 mg/day 1, 2

Practical Dosing Calculation

• For most 15-year-olds weighing 50-60 kg: This translates to approximately 2000-2700 mg twice daily, but capped at the maximum adult dose of 2000 mg twice daily (4000 mg/day total) 1, 2
• Standard prescription: Amoxicillin 2000 mg PO twice daily (or one 2000-mg extended-release tablet twice daily) 1
• Alternative formulation: If using standard 500-mg tablets, prescribe four 500-mg tablets (2000 mg) twice daily 1

Clinical Context and Rationale

Why High-Dose Amoxicillin?

• High-dose therapy (90 mg/kg/day) is specifically designed to overcome penicillin-resistant Streptococcus pneumoniae, the most common bacterial cause of CAP 1, 2
• This dosing achieves adequate serum and epithelial lining fluid concentrations to maintain free drug levels above the MIC for 30-50% of the dosing interval 3
• Recent surveillance data shows that high-dose amoxicillin achieves >93% probability of target attainment in serum for pneumococcal pneumonia 3

When to Consider Macrolide Addition

• If the patient has clinical features suggesting atypical pneumonia (e.g., gradual onset, prominent cough, minimal fever, normal white blood cell count), add azithromycin 500 mg on day 1, then 250 mg daily on days 2-5 1
• For adolescents ≥5 years old who cannot distinguish bacterial from atypical CAP based on clinical presentation, a macrolide can be added empirically to the β-lactam 1

Alternative Regimens

If Amoxicillin Cannot Be Used

• Amoxicillin-clavulanate: 90 mg/kg/day (amoxicillin component) in 2 doses, maximum 4000 mg/day 1, 2
• For β-lactam allergy: Consider levofloxacin (for adolescents who have reached growth maturity) or a macrolide alone if atypical pathogen is suspected 1

Common Pitfalls to Avoid

Underdosing

• Do not use standard adult dosing of 500 mg three times daily – this provides only 1500 mg/day, which is inadequate for resistant pneumococcus 2, 3
• Standard-dose amoxicillin (15 mg/kg/dose three times daily) achieves only 4% probability of target attainment using CLSI breakpoints 3

Duration of Therapy

• Recent evidence supports shorter courses: 3-day treatment demonstrated non-inferiority to 7-day treatment for uncomplicated CAP, though cough resolution was slightly faster with 7 days 4
• Practical recommendation: Prescribe 5-7 days for outpatient pneumonia, with reassessment if symptoms persist beyond 48-72 hours 1

Twice-Daily vs. Three-Times-Daily Dosing

• Twice-daily dosing at 90 mg/kg/day is preferred over three-times-daily dosing at lower doses because it improves adherence and achieves superior pharmacokinetic profiles 1, 5
• Studies show that 25 mg/kg twice daily achieves higher AUC than 15 mg/kg three times daily 5