What is the best treatment plan for an otherwise healthy adult with community-acquired pneumonia?

Best Treatment Plan for Community-Acquired Pneumonia in Healthy Adults

Outpatient Treatment (Healthy Adults Without Comorbidities)

Amoxicillin 1 g orally three times daily for 5-7 days is the preferred first-line therapy for otherwise healthy adults with community-acquired pneumonia. 1

• This recommendation carries strong evidence and moderate quality data supporting its effectiveness against common CAP pathogens including Streptococcus pneumoniae, Haemophilus influenzae, and Moraxella catarrhalis 1
• Doxycycline 100 mg orally twice daily serves as an acceptable alternative, though this carries lower quality evidence 1
• Avoid macrolide monotherapy (azithromycin, clarithromycin) unless local pneumococcal macrolide resistance is documented to be <25%, as resistance rates exceeding this threshold lead to treatment failure 1, 2

Inpatient Treatment (Non-ICU Hospitalized Patients)

For hospitalized patients not requiring ICU admission, use either ceftriaxone 1-2 g IV daily plus azithromycin 500 mg daily, or respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily). 1

• Both regimens carry strong recommendations with high-quality evidence and demonstrate equivalent efficacy 1
• Administer the first antibiotic dose immediately in the emergency department, as delayed administration beyond 8 hours increases 30-day mortality by 20-30% 1, 3
• Obtain blood cultures and sputum Gram stain/culture before initiating antibiotics in all hospitalized patients 1
• Transition from IV to oral therapy when the patient is hemodynamically stable, clinically improving, afebrile for 48-72 hours, able to take oral medications, and has normal GI function—typically by day 2-3 of hospitalization 1

Severe CAP Requiring ICU Admission

All ICU patients require mandatory combination therapy with a β-lactam (ceftriaxone 2 g IV daily, cefotaxime 1-2 g IV every 8 hours, or ampicillin-sulbactam 3 g IV every 6 hours) plus either azithromycin 500 mg IV daily or a respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily). 1, 2

• Monotherapy is inadequate for severe disease and increases mortality risk 1
• This combination provides coverage for both typical bacterial pathogens and atypical organisms (Mycoplasma, Chlamydophila, Legionella) 1

Duration of Therapy

Treat for a minimum of 5 days and until the patient is afebrile for 48-72 hours with no more than one sign of clinical instability. 1, 2

• The typical duration for uncomplicated CAP is 5-7 days 1, 4
• Meta-analyses confirm that short-course regimens (≤7 days) have equivalent clinical cure rates with fewer adverse events compared to longer courses 4, 5
• Extend duration to 14-21 days only for specific pathogens: Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli (including E. coli) 1, 6

Special Considerations for Drug-Resistant Pathogens

Pseudomonas aeruginosa Risk Factors

Add antipseudomonal coverage only when specific risk factors are present: structural lung disease (bronchiectasis, COPD), recent hospitalization with IV antibiotics within 90 days, or prior respiratory isolation of P. aeruginosa 1

• Use antipseudomonal β-lactam (piperacillin-tazobactam, cefepime, imipenem, or meropenem) plus ciprofloxacin 400 mg IV every 8 hours or levofloxacin 750 mg IV daily 1

MRSA Risk Factors

Add MRSA coverage only when specific risk factors are present: prior MRSA infection/colonization, recent hospitalization with IV antibiotics, post-influenza pneumonia, or cavitary infiltrates on imaging 1

• Add vancomycin 15 mg/kg IV every 8-12 hours (target trough 15-20 mg/mL) or linezolid 600 mg IV every 12 hours to the base regimen 1

Critical Pitfalls to Avoid

• Never use macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25%, as macrolide-resistant S. pneumoniae may also be resistant to doxycycline 1
• Avoid indiscriminate fluoroquinolone use in uncomplicated outpatient CAP due to FDA warnings about serious adverse events and resistance concerns 1
• Do not extend therapy beyond 7 days in responding patients without specific indications (such as Legionella, S. aureus, or Gram-negative bacilli), as this increases antimicrobial resistance risk without improving outcomes 1
• Never delay antibiotic administration beyond 8 hours in hospitalized patients, as this significantly increases mortality 1, 3

Oral Step-Down Options for Hospitalized Patients

When transitioning from IV to oral therapy, use:

• Amoxicillin 1 g orally three times daily plus azithromycin 500 mg orally daily 1
• Alternatively, amoxicillin-clavulanate 875 mg/125 mg orally twice daily plus azithromycin 500 mg orally daily 1
• Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg orally daily or moxifloxacin 400 mg orally daily) 1, 7