For a 17-year-old female with community-acquired pneumonia, should I use pediatric dosing or adult dosing for antibiotics?

Antibiotic Dosing for a 17-Year-Old with Community-Acquired Pneumonia

Use adult dosing for a 17-year-old girl with community-acquired pneumonia. At this age, patients have reached skeletal maturity and should be dosed according to adult regimens rather than weight-based pediatric calculations 1.

Primary Recommendation

Prescribe amoxicillin 1000 mg (one 2000-mg tablet divided or two 500-mg tablets) twice daily for 5-7 days as first-line therapy for outpatient community-acquired pneumonia 1. This regimen provides the high-dose coverage (approximately 90 mg/kg/day for most adolescents) needed to overcome penicillin-resistant Streptococcus pneumoniae, the most common bacterial cause of CAP 1.

Key Dosing Principles

• Maximum daily dose is 4 grams per day regardless of weight, which serves as the ceiling for amoxicillin therapy 1, 2
• The twice-daily dosing at this high dose improves adherence and achieves superior pharmacokinetic profiles compared to three-times-daily regimens 1
• For adolescents with skeletal maturity (generally ≥16 years), adult formulations and standard adult dosing regimens are appropriate 1

When to Add Atypical Coverage

Add azithromycin 500 mg on day 1, then 250 mg daily on days 2-5 if the patient presents with clinical features suggesting atypical pneumonia (Mycoplasma pneumoniae or Chlamydophila pneumoniae), such as gradual onset, prominent cough, or lack of consolidation on imaging 1, 3.

Alternative for Atypical Coverage

• Doxycycline 100 mg twice daily is an acceptable alternative to azithromycin for adolescents with skeletal maturity (≥16 years), but must always be combined with a β-lactam—never use as monotherapy because it lacks adequate coverage for S. pneumoniae 1
• Counsel patients taking doxycycline to take it with a full glass of water, remain upright for 30 minutes, avoid dairy/calcium/iron within 2 hours, and use sunscreen SPF ≥30 1

β-Lactam Allergy Alternatives

Non-Anaphylactic Penicillin Allergy

• Levofloxacin 500 mg once daily for 5-7 days provides coverage for both typical and atypical pathogens 1

Type I (IgE-Mediated) Penicillin Allergy

• Levofloxacin 500 mg once daily or moxifloxacin 400 mg once daily for 5-7 days 1
• Alternatively, azithromycin monotherapy may be used, though it has inferior efficacy compared to β-lactams 1

Treatment Duration and Monitoring

• Prescribe 5-7 days of therapy for outpatient pneumonia, which is sufficient for most cases 1
• Reassess if symptoms persist beyond 48-72 hours, as clinical improvement should be evident within this timeframe 1, 4
• Fever typically resolves within 24-48 hours for pneumococcal pneumonia, though cough may persist longer 1

Common Pitfalls to Avoid

• Do not use pediatric weight-based dosing (e.g., 90 mg/kg/day) in a 17-year-old, as this may result in excessive doses beyond the 4-gram daily maximum 1, 2
• Do not prescribe doxycycline as monotherapy for CAP in adolescents—it must be combined with amoxicillin because it does not adequately cover S. pneumoniae 1
• Do not use amoxicillin-clavulanate as first-line therapy unless the patient has risk factors for β-lactamase-producing organisms (recent antibiotic use, incomplete H. influenzae type b vaccination, or concurrent purulent otitis media) 5, 1

When to Consider Hospitalization

• If the patient shows no improvement after 5 days of appropriate outpatient therapy, hospitalization should be considered 1
• For hospitalized patients without risk factors for resistant bacteria, ceftriaxone 1-2 grams IV daily combined with azithromycin 500 mg IV/PO daily is the preferred regimen for a minimum of 3 days 6