What is the recommended amoxicillin dose, schedule, and duration for an otherwise healthy 15‑year‑old with community‑acquired pneumonia caused by typical bacteria?

Amoxicillin Treatment for Pneumonia in a 15-Year-Old

For an otherwise healthy 15-year-old with community-acquired pneumonia, prescribe high-dose oral amoxicillin 90 mg/kg/day divided into two doses (maximum 4 g/day) for 7 days. 1

Dosing Calculation and Administration

• Calculate the total daily dose: Multiply the patient's weight in kg by 90 mg/kg/day, then divide by 2 to determine each individual dose 1
• Maximum limits: Do not exceed 2,000 mg per single dose or 4,000 mg total per day, regardless of weight 1, 2
• Dosing schedule: Administer every 12 hours (twice daily) 1, 2

For example, a 50 kg adolescent would receive 4,500 mg/day calculated dose, but this is capped at the maximum of 4,000 mg/day (2,000 mg twice daily). 2

Treatment Duration

• Standard duration is 7 days for uncomplicated community-acquired pneumonia 1, 3, 4
• Some evidence supports 5-day courses may be equally effective, but current major guidelines maintain 7-10 days as the standard recommendation 1, 5
• Continue treatment for a minimum of 48-72 hours after complete symptom resolution 2

Rationale for High-Dose Regimen

The 90 mg/kg/day dosing is essential for adolescents with pneumonia because:

• It provides adequate coverage against penicillin-resistant Streptococcus pneumoniae with MICs up to 2-4 mg/L 1, 2, 6
• S. pneumoniae remains the most common bacterial cause of community-acquired pneumonia in all pediatric age groups 1
• Lower doses (45 mg/kg/day) are insufficient for pneumonia, though they may be adequate for other respiratory infections 2

When to Add Atypical Coverage

For patients ≥5 years old (including adolescents), consider adding a macrolide to the β-lactam regimen if:

• Clinical, laboratory, or radiographic features do not clearly distinguish bacterial from atypical pneumonia 1
• No improvement occurs within 48-72 hours of amoxicillin therapy 1, 3
• Mycoplasma pneumoniae or Chlamydia pneumoniae are suspected based on epidemiology or presentation 1

Macrolide options include:

• Azithromycin: 10 mg/kg on day 1 (max 500 mg), then 5 mg/kg/day on days 2-5 (max 250 mg) 1
• Doxycycline: appropriate alternative for children >7 years old 1

However, amoxicillin monotherapy is appropriate for most adolescents with presumed bacterial pneumonia, as atypical bacteria do not require empiric coverage in every case. 7

Monitoring and Expected Response

Clinical improvement should occur within 48-72 hours, including:

• Fever resolution (typically within 24-48 hours for pneumococcal pneumonia) 2, 3, 4
• Decreased respiratory rate and reduced work of breathing 3, 4
• Improved oxygen saturation if initially hypoxemic 3

If no improvement or deterioration occurs by 48-72 hours, investigate for:

• Inadequate antibiotic dosing or inappropriate drug selection 3
• Atypical pathogens requiring macrolide addition 1, 3
• Complications such as parapneumonic effusion or empyema 1
• Resistant organisms or alternative diagnoses 3

Alternative Regimens

For penicillin-allergic patients:

• Non-anaphylactic reactions: Use second- or third-generation cephalosporins (cefdinir, cefuroxime, cefpodoxime) under medical supervision 1, 2
• Type I hypersensitivity (anaphylaxis): Use a respiratory fluoroquinolone (levofloxacin for growth-mature adolescents) or linezolid 1

For suspected β-lactamase-producing organisms (H. influenzae, M. catarrhalis):

• Switch to amoxicillin-clavulanate 90 mg/kg/day of the amoxicillin component (maximum 4,000 mg/day) divided twice daily 1, 2

Hospitalization Criteria

Admit to hospital if any of the following are present:

• Oxygen saturation <92% on room air 3, 4
• Moderate to severe respiratory distress with increased work of breathing 3, 4
• Inability to tolerate oral intake or medications 3, 4
• Hemodynamic instability requiring vasopressor support 3
• Suspected community-acquired MRSA infection 1, 3

For hospitalized patients requiring parenteral therapy, use ampicillin 150-200 mg/kg/day IV every 6 hours or penicillin G, then switch to oral amoxicillin when clinically stable. 1, 3

Common Pitfalls to Avoid

• Do not use standard-dose amoxicillin (45 mg/kg/day) for pneumonia—this dose is inadequate for pneumococcal coverage 2, 6
• Do not use macrolide monotherapy in adolescents with presumed bacterial pneumonia, as it provides inadequate coverage for S. pneumoniae 3
• Do not routinely obtain chest radiographs in well-appearing outpatients, as this leads to overdiagnosis 3, 4
• Do not continue antibiotics beyond 7 days for uncomplicated pneumonia that has resolved 1, 3, 5