How should I assess severity and manage a typical adult with community‑acquired pneumonia, including outpatient, inpatient, and ICU antibiotic regimens and adjustments for drug allergies?

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Last updated: February 27, 2026 • View editorial policy

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Management of Community-Acquired Pneumonia in Adults

Severity Assessment and Site-of-Care Decision

Use validated severity scores (PSI or CURB-65) combined with clinical judgment to determine whether hospitalization is required. 1

  • Outpatient management is appropriate for PSI class I–III or CURB-65 score 0–1, provided the patient has no unstable comorbidities, can reliably take oral medication, and has adequate home support. 1
  • Hospital admission is indicated for PSI class IV–V or CURB-65 score ≥2 (confusion, respiratory rate ≥30/min, systolic BP <90 mmHg, age ≥65 years). 1
  • ICU admission is required when any one major criterion is met (septic shock requiring vasopressors or respiratory failure requiring mechanical ventilation) or when ≥3 minor criteria are present (confusion, respiratory rate ≥30/min, systolic BP <90 mmHg, multilobar infiltrates, PaO₂/FiO₂ <250). 1

Outpatient Antibiotic Regimens

Previously Healthy Adults (No Comorbidities)

First-line therapy is amoxicillin 1 g orally three times daily for 5–7 days, which retains activity against 90–95% of Streptococcus pneumoniae isolates, including many penicillin-resistant strains. 1

  • Doxycycline 100 mg orally twice daily is an acceptable alternative when amoxicillin is contraindicated. 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%; in most U.S. regions resistance is 20–30%, making macrolide monotherapy unsafe as first-line. 1, 2

Adults with Comorbidities or Recent Antibiotic Use

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

  • Option 1 (preferred): Amoxicillin-clavulanate 875/125 mg orally twice daily plus azithromycin (500 mg day 1, then 250 mg daily) or doxycycline 100 mg twice daily for 5–7 days. 1
  • Option 2: Respiratory fluoroquinolone monotherapy—levofloxacin 750 mg daily or moxifloxacin 400 mg daily for 5–7 days—reserved for β-lactam allergy or when combination therapy is contraindicated due to FDA safety warnings (tendon rupture, peripheral neuropathy, aortic dissection). 1, 2

Inpatient (Non-ICU) Antibiotic Regimens

Two equally effective regimens exist with strong evidence: 1

Preferred Regimen

Ceftriaxone 1–2 g IV once daily plus azithromycin 500 mg IV or orally daily, providing coverage for typical pathogens (S. pneumoniae, H. influenzae, M. catarrhalis) and atypical organisms (Mycoplasma, Chlamydophila, Legionella). 1, 3

  • Alternative β-lactams include 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) is equally effective and preferred for penicillin-allergic patients. 1

ICU (Severe CAP) Antibiotic Regimens

Combination therapy is mandatory for all ICU patients; β-lactam monotherapy is associated with higher mortality. 1, 3

Standard ICU Regimen

Ceftriaxone 2 g IV once 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 a respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily). 1

Penicillin-Allergic ICU Patients

Aztreonam 2 g IV every 8 hours plus a respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily). 1

Special Pathogen Coverage (Risk-Based)

Pseudomonas aeruginosa Coverage

Add antipseudomonal therapy only when specific risk factors are present: structural lung disease (bronchiectasis, cystic fibrosis), recent hospitalization with IV antibiotics within 90 days, prior respiratory isolation of P. aeruginosa, or chronic broad-spectrum antibiotic exposure (≥7 days in past month). 1

  • Regimen: Antipseudomonal β-lactam (piperacillin-tazobactam 4.5 g IV every 6 hours or cefepime 2 g IV every 8 hours or meropenem 1 g IV every 8 hours) plus ciprofloxacin 400 mg IV every 8 hours or levofloxacin 750 mg IV daily plus an aminoglycoside (gentamicin or tobramycin 5–7 mg/kg IV daily) for dual antipseudomonal coverage. 1

MRSA Coverage

Add MRSA therapy only when risk factors are present: prior MRSA infection/colonization, recent hospitalization with IV antibiotics within 90 days, post-influenza pneumonia, or cavitary infiltrates on imaging. 1

  • Regimen: Vancomycin 15 mg/kg IV every 8–12 hours (target trough 15–20 µg/mL) or linezolid 600 mg IV every 12 hours, added to the base CAP regimen. 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 (temperature ≤37.8°C, heart rate ≤100 bpm, respiratory rate ≤24 breaths/min, systolic BP ≥90 mmHg, oxygen saturation ≥90% on room air, able to maintain oral intake, normal mental status). 1, 3

  • Typical duration for uncomplicated CAP is 5–7 days. 1, 3
  • Extended courses (14–21 days) are required only for specific pathogens: Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli. 1

Transition from IV to Oral Therapy

Switch 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, and able to take oral medication—typically by hospital day 2–3. 1

  • Oral step-down options: Amoxicillin 1 g three times daily plus azithromycin 500 mg daily (or azithromycin alone after 2–3 days of IV therapy). 1

Critical Timing and Diagnostic Considerations

Administer the first antibiotic dose immediately in the emergency department upon diagnosis; delays beyond 8 hours increase 30-day mortality by 20–30% in hospitalized patients. 1, 3

Obtain blood cultures and sputum Gram stain/culture before initiating antibiotics in all hospitalized patients to enable pathogen-directed therapy and safe de-escalation. 1

Adjustments for Drug Allergies

Penicillin Allergy (Hospitalized Patients)

  • Non-ICU: Respiratory fluoroquinolone monotherapy (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily). 1
  • ICU: Aztreonam 2 g IV every 8 hours plus respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily). 1

Macrolide Allergy or Contraindication

  • Substitute doxycycline 100 mg twice daily for azithromycin in combination regimens (conditional recommendation, lower quality evidence). 1

Fluoroquinolone Allergy (ICU Patients)

  • Ceftriaxone 2 g IV daily plus azithromycin 500 mg IV daily (or clarithromycin 500 mg twice daily as azithromycin substitute). 1

Common Pitfalls to Avoid

  • Never use macrolide monotherapy in hospitalized patients—it fails to cover typical pathogens like S. pneumoniae and leads to treatment failure. 1
  • Avoid macrolide monotherapy in outpatients when local pneumococcal macrolide resistance exceeds 25%—this increases risk of breakthrough bacteremia and treatment failure. 1, 2
  • Do not add broad-spectrum antipseudomonal or MRSA agents routinely—restrict to patients with documented risk factors to prevent unnecessary resistance and adverse effects. 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
  • Do not delay antibiotic administration to obtain cultures—specimens should be collected rapidly, but therapy must start immediately. 1

Follow-Up and Monitoring

  • Outpatients: Clinical review at 48 hours (or sooner if symptoms worsen) to assess response, oral intake, and adherence. 1
  • Hospitalized patients: Monitor temperature, respiratory rate, pulse, blood pressure, mental status, and oxygen saturation at least twice daily. 1
  • All patients: Routine follow-up at 6 weeks; chest radiograph only if symptoms persist, physical signs remain abnormal, or high risk for underlying malignancy (e.g., smokers >50 years). 1

Treatment Failure Recognition

If no clinical improvement by day 2–3, obtain repeat chest radiograph, inflammatory markers (CRP, white blood cell count), and additional microbiologic specimens to evaluate for complications (pleural effusion, empyema) or resistant organisms. 1

  • For non-severe pneumonia on amoxicillin monotherapy: Add or substitute a macrolide. 1
  • For non-severe pneumonia on combination therapy: Switch to respiratory fluoroquinolone. 1
  • For severe pneumonia not responding to combination therapy: Consider adding rifampicin. 1

References

1
Guideline

Antibiotic Regimen Recommendations for Community-Acquired Pneumonia in Adults

Praxis Medical Insights: Practical Summaries of Clinical Guidelines, 2026

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Professional Medical Disclaimer

This information is intended for healthcare professionals. Any medical decision-making should rely on clinical judgment and independently verified information. The content provided herein does not replace professional discretion and should be considered supplementary to established clinical guidelines. Healthcare providers should verify all information against primary literature and current practice standards before application in patient care. Dr.Oracle assumes no liability for clinical decisions based on this content.

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