What are the initial antibiotic therapy recommendations for an adult patient with community-acquired pneumonia (CAP) in 2020?

Community-Acquired Pneumonia (CAP) Antibiotic Guidelines for Adults (2020)

Outpatient Treatment

Previously Healthy Adults Without Comorbidities

• Amoxicillin 1 g orally three times daily for 5-7 days is the preferred first-line therapy, based on strong recommendation and moderate-quality evidence from the American Thoracic Society 1
• Doxycycline 100 mg orally twice daily serves as an acceptable alternative, though this carries a conditional recommendation with lower quality evidence 1
• Macrolides (azithromycin 500 mg day 1, then 250 mg daily; or clarithromycin 500 mg twice daily) should ONLY be used in areas where pneumococcal macrolide resistance is documented <25% 1, 2

Adults With Comorbidities (COPD, diabetes, heart/liver/renal disease, malignancy)

• Combination therapy is mandatory: β-lactam (amoxicillin-clavulanate 875/125 mg twice daily, cefpodoxime, or cefuroxime) PLUS macrolide (azithromycin or clarithromycin) OR doxycycline 1, 2
• Alternative: Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily, moxifloxacin 400 mg daily, or gemifloxacin 320 mg daily) 1, 2

Hospitalized Non-ICU Patients

Two equally effective regimens exist with strong recommendations and high-quality evidence 1:

Preferred Regimen

• Ceftriaxone 1-2 g IV daily PLUS azithromycin 500 mg daily (IV or oral) 1, 3
• Alternative β-lactams: cefotaxime 1-2 g IV every 8 hours OR ampicillin-sulbactam 3 g IV every 6 hours, always combined with azithromycin 1

Alternative Regimen

• Respiratory fluoroquinolone monotherapy: levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily 1, 4
• For penicillin-allergic patients, respiratory fluoroquinolone is the preferred alternative 1

Severe CAP Requiring ICU Admission

Combination therapy is MANDATORY for all ICU patients—monotherapy is inadequate and associated with higher mortality 1, 5:

• Ceftriaxone 2 g IV daily (or 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 respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 1, 5
• Administer the first antibiotic dose immediately upon diagnosis, ideally within the first hour of ICU admission, as delayed administration increases mortality 5

Special Pathogen Coverage

Pseudomonas aeruginosa Risk Factors

Add antipseudomonal coverage ONLY when these risk factors are present 1, 5:

• Structural lung disease (bronchiectasis)
• Recent hospitalization with IV antibiotics within 90 days
• Prior respiratory isolation of P. aeruginosa

Regimen: Antipseudomonal β-lactam (piperacillin-tazobactam 4.5 g IV every 6 hours, cefepime 2 g IV every 8 hours, imipenem, or meropenem) PLUS ciprofloxacin 400 mg IV every 8 hours OR levofloxacin 750 mg IV daily PLUS aminoglycoside (gentamicin or tobramycin 5-7 mg/kg IV daily) 1, 5

MRSA Risk Factors

Add MRSA coverage ONLY when these risk factors are present 1, 5:

• Prior MRSA infection or colonization
• Recent hospitalization with IV antibiotics
• Post-influenza pneumonia
• Cavitary infiltrates on imaging

Regimen: 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

Duration of Therapy

• Minimum of 5 days AND until the patient is afebrile for 48-72 hours with no more than one sign of clinical instability 1, 5, 3
• Typical duration for uncomplicated CAP is 5-7 days 1, 6
• Extended duration (14-21 days) required for: Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli 1, 5

Transition to Oral Therapy

Switch from IV to oral antibiotics when ALL of the following criteria are met 1, 5:

• Hemodynamically stable
• Clinically improving
• Able to take oral medications
• Normal gastrointestinal function
• Typically achievable by day 2-3 of hospitalization

Critical Pitfalls to Avoid

• NEVER delay antibiotic administration beyond 8 hours in hospitalized patients—this increases 30-day mortality by 20-30% 1, 5
• NEVER use macrolide monotherapy in hospitalized patients—provides inadequate coverage for typical bacterial pathogens like S. pneumoniae 1
• NEVER use macrolides in areas where pneumococcal macrolide resistance exceeds 25%—leads to treatment failure 1, 2
• ALWAYS obtain blood cultures and sputum Gram stain/culture before initiating antibiotics in ALL hospitalized patients to allow pathogen-directed therapy 1, 5
• AVOID indiscriminate fluoroquinolone use in uncomplicated outpatient CAP due to resistance concerns and serious adverse events 1
• DO NOT add antipseudomonal or MRSA coverage without documented risk factors—this promotes resistance 1