What is the recommended management and antibiotic regimen for a typical adult with community‑acquired pneumonia, including severity assessment and outpatient versus inpatient treatment?

Management of Community-Acquired Pneumonia in Adults

Severity Assessment and Site-of-Care Decision

Use the Pneumonia Severity Index (PSI) or CURB-65 score to determine whether outpatient or inpatient treatment is appropriate, as these validated tools predict 30-day mortality and guide initial management decisions. 1

• PSI Classes I–III: Treat as outpatient 1, 2
• PSI Classes IV–V: Consider hospitalization 1, 3
• CURB-65 score ≥2: Hospitalize the patient 1, 4
• ICU admission criteria: Presence of septic shock requiring vasopressors, respiratory failure requiring mechanical ventilation, or ≥3 minor criteria (confusion, respiratory rate ≥30/min, hypotension, multilobar infiltrates, hypothermia, leukopenia, thrombocytopenia, uremia, hypoxemia) 1

The modified BTS severity score performs best across multiple outcomes including mortality and ICU admission, while PSI Classes IV+V and CURB demonstrate similar predictive accuracy 4. However, PSI is significantly better than CURB-65 for predicting 30-day mortality (94% vs 62% sensitivity) and ICU admission (86% vs 61% sensitivity) 3.

Outpatient Antibiotic Regimens

Previously Healthy Adults Without Comorbidities

Amoxicillin 1 g orally three times daily for 5–7 days is the preferred first-line therapy, providing superior pneumococcal coverage including drug-resistant strains. 1

• Alternative: Doxycycline 100 mg orally twice daily for 5–7 days 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, 5

Adults With Comorbidities or Recent Antibiotic Use

Combination therapy is required for patients with COPD, diabetes, chronic heart/liver/renal disease, malignancy, or antibiotic use within 90 days. 1

• Option 1: β-lactam (amoxicillin-clavulanate 875/125 mg twice daily, cefpodoxime, or cefuroxime) plus macrolide (azithromycin or clarithromycin) or doxycycline 100 mg twice daily 1
• Option 2: Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg daily or moxifloxacin 400 mg daily) 1

Inpatient Antibiotic Regimens (Non-ICU)

For hospitalized patients not requiring ICU admission, use either β-lactam plus macrolide combination or respiratory fluoroquinolone monotherapy—both regimens have equivalent efficacy with strong evidence. 1

• Preferred regimen: Ceftriaxone 1–2 g IV daily plus azithromycin 500 mg IV or oral daily 1
• 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 monotherapy: Levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily 1
• Penicillin-allergic patients: Use respiratory fluoroquinolone 1

Administer the first antibiotic dose in the emergency department immediately upon diagnosis, as delays beyond 8 hours increase 30-day mortality by 20–30%. 1

Severe CAP Requiring ICU Admission

Combination therapy is mandatory for all ICU patients; β-lactam monotherapy is associated with higher mortality. 1

• Preferred ICU regimen: Ceftriaxone 2 g IV daily (or cefotaxime 1–2 g IV every 8 hours or ampicillin-sulbactam 3 g IV every 6 hours) plus azithromycin 500 mg IV daily or respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 1

Special Pathogen Coverage (Add Only When Risk Factors Present)

Antipseudomonal coverage: Add only if structural lung disease (bronchiectasis, cystic fibrosis), recent hospitalization with IV antibiotics within 90 days, or prior Pseudomonas aeruginosa isolation 1

• Regimen: Piperacillin-tazobactam 4.5 g IV every 6 hours or cefepime 2 g IV every 8 hours 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

MRSA coverage: Add only if prior MRSA infection/colonization, recent hospitalization with IV antibiotics, post-influenza pneumonia, or cavitary infiltrates on imaging 1

• Regimen: Vancomycin 15 mg/kg IV every 8–12 hours (target trough 15–20 mg/L) or linezolid 600 mg IV every 12 hours 1

Duration of Therapy

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

• Typical duration for uncomplicated CAP: 5–7 days 1, 5
• Extended duration (14–21 days): Required for Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli 1, 5
• Severe microbiologically undefined pneumonia: 10 days 5

Transition from IV to Oral Therapy

Switch from IV to oral antibiotics when the patient is hemodynamically stable (systolic BP ≥90 mmHg, heart rate ≤100 bpm), clinically improving, afebrile for 48–72 hours, respiratory rate ≤24 breaths/min, oxygen saturation ≥90% on room air, able to take oral medications, and has normal GI function—typically by hospital day 2–3. 1, 5

• Oral step-down options: Amoxicillin 1 g three times daily plus azithromycin 500 mg daily, or continue respiratory fluoroquinolone 1

Supportive Care and Monitoring

All hospitalized patients require appropriate oxygen therapy targeting PaO₂ >8 kPa (60 mmHg) and SaO₂ >92%. 5

• High-flow oxygen is safe in uncomplicated pneumonia 5
• For COPD patients with ventilatory failure, guide oxygen therapy by repeated arterial blood gases to avoid CO₂ retention 5
• Monitor temperature, respiratory rate, pulse, blood pressure, mental status, oxygen saturation, and inspired oxygen concentration at least twice daily 5
• Assess for volume depletion and provide IV fluids as needed 5

Follow-Up and Treatment Failure

Review outpatients at 48 hours or sooner if clinically indicated to assess treatment response. 5, 1

If no clinical improvement by day 2–3, obtain repeat chest radiograph, CRP, white cell count, and additional microbiological specimens. 5

• For non-severe pneumonia on amoxicillin monotherapy: Add or substitute a macrolide 5
• For non-severe pneumonia on combination therapy: Switch to respiratory fluoroquinolone 5
• For severe pneumonia not responding to combination therapy: Consider adding rifampicin 5

Schedule clinical review at 6 weeks for all hospitalized patients; chest radiograph is only required for those with persistent symptoms, physical signs, or high risk for underlying malignancy (smokers >50 years). 5, 1

Critical Pitfalls to Avoid

• Never use macrolide monotherapy in hospitalized patients—it provides inadequate coverage for typical bacterial pathogens like S. pneumoniae 1
• Never use macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25%—this leads to treatment failure and breakthrough bacteremia 1
• Never delay antibiotic administration beyond 8 hours—this increases 30-day mortality by 20–30% 1
• Obtain blood and sputum cultures before initiating antibiotics in all hospitalized patients to enable pathogen-directed therapy and de-escalation 1
• Avoid indiscriminate use of antipseudomonal or MRSA coverage—add only when documented risk factors are present 1
• Do not extend therapy beyond 7–8 days in responding patients without specific indications—longer courses increase antimicrobial resistance risk without improving outcomes 1

Prevention

• Administer pneumococcal polysaccharide vaccine to all patients ≥65 years and those with high-risk conditions 5, 1
• Offer annual influenza vaccination to all patients, especially those with chronic medical illnesses 5, 1
• Make smoking cessation a goal for all patients hospitalized with CAP who smoke 5, 1