Community-Acquired Pneumonia Treatment Algorithm
Initial Assessment and Site-of-Care Decision
The first critical decision is determining whether the patient requires outpatient treatment, hospital admission to a medical ward, or ICU-level care, which fundamentally determines the antibiotic regimen. 1
- Use validated severity scores (PSI or CURB-65) to guide hospitalization decisions, with PSI classes I-III typically managed outpatient and classes IV-V considered for admission 1
- Assess for severe CAP requiring ICU admission based on need for vasopressors or mechanical ventilation 1
- Administer the first antibiotic dose in the emergency department immediately upon diagnosis—delayed administration beyond 8 hours increases 30-day mortality by 20-30% 1, 2
Outpatient Treatment Algorithm
For Previously Healthy Adults Without Comorbidities
Amoxicillin 1 gram orally three times daily is the preferred first-line therapy for healthy adults without comorbidities or recent antibiotic exposure. 1
- Doxycycline 100 mg orally twice daily serves as an acceptable alternative if amoxicillin cannot be tolerated 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
- Avoid macrolide monotherapy in areas with high resistance rates to prevent treatment failure 1
For Adults With Comorbidities or Recent Antibiotic Use
Use combination therapy with a β-lactam plus macrolide, OR respiratory fluoroquinolone monotherapy. 1
- Combination regimen: β-lactam (amoxicillin-clavulanate 2 g twice daily, cefpodoxime, or cefuroxime) PLUS macrolide (azithromycin or clarithromycin) OR doxycycline 1, 2
- Fluoroquinolone monotherapy: Levofloxacin 750 mg daily, moxifloxacin 400 mg daily, or gemifloxacin 320 mg daily 1, 3
- Reserve fluoroquinolones for patients who have failed first-line therapy, have allergies to alternative agents, or have documented highly drug-resistant pneumococci (penicillin MIC ≥4 mcg/mL) to limit resistance development 4
Inpatient Non-ICU Treatment Algorithm
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 Regimens (Equal Efficacy)
β-lactam plus macrolide: Ceftriaxone 1-2 g IV daily PLUS azithromycin 500 mg daily 1, 5
Respiratory fluoroquinolone monotherapy: Levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily 1, 3
For Penicillin-Allergic Patients
- Use respiratory fluoroquinolone (levofloxacin or moxifloxacin) as the preferred alternative 1
- Alternative: Aztreonam 2 g IV every 8 hours PLUS azithromycin 500 mg IV daily if fluoroquinolones are contraindicated 1
Critical Pitfall to Avoid
Never use cefuroxime, cefepime, piperacillin-tazobactam, or carbapenems as first-line empiric therapy unless specific risk factors for Pseudomonas or MRSA are present—these agents have inferior outcomes for standard CAP. 1
ICU-Level Severe CAP Treatment Algorithm
All ICU patients with severe CAP require mandatory combination therapy with a β-lactam PLUS either azithromycin OR a respiratory fluoroquinolone. 1, 2
Standard ICU Regimen
- β-lactam: Ceftriaxone 2 g IV daily, cefotaxime 1-2 g IV every 8 hours, OR ampicillin-sulbactam 3 g IV every 6 hours 1
- PLUS azithromycin 500 mg IV daily 1, 5
- OR PLUS respiratory fluoroquinolone: Levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily 1, 3
For Penicillin-Allergic ICU Patients
- Respiratory fluoroquinolone (levofloxacin 750 mg IV daily) PLUS aztreonam 2 g IV every 8 hours 1
Special Populations Requiring Broader Coverage
Risk Factors for Pseudomonas aeruginosa
Add antipseudomonal coverage if the patient has structural lung disease (bronchiectasis), recent hospitalization with IV antibiotics within 90 days, or prior respiratory isolation of P. aeruginosa. 1
- Antipseudomonal 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 5-7 mg/kg IV daily or tobramycin 5-7 mg/kg IV daily) PLUS azithromycin 1
Risk Factors for MRSA
Add MRSA coverage if the patient has prior MRSA infection/colonization, recent hospitalization with IV antibiotics, post-influenza pneumonia, or cavitary infiltrates on imaging. 1
- Add to base regimen: Vancomycin 15 mg/kg IV every 8-12 hours (target trough 15-20 mg/mL) OR linezolid 600 mg IV every 12 hours 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—typical duration for uncomplicated CAP is 5-7 days. 1, 2
- Extend duration to 14-21 days for Legionella pneumophila, Staphylococcus aureus, or Gram-negative enteric bacilli 6, 1
- For severe microbiologically undefined pneumonia, 10 days of treatment is recommended 6
Transition to Oral Therapy
Switch from IV to oral antibiotics when the patient is hemodynamically stable, clinically improving, able to take oral medications, and has normal GI function—typically by day 2-3 of hospitalization. 6, 1
- Oral step-down regimen: Amoxicillin 1 g orally three times daily PLUS azithromycin 500 mg orally daily 1
- Alternative macrolide: Clarithromycin 500 mg orally twice daily 1
- Continue total antibiotic duration as outlined above 1
Failure to Improve
If no clinical improvement by day 2-3, obtain repeat chest radiograph, CRP, white cell count, and additional microbiological specimens. 6
- For non-severe pneumonia initially treated with amoxicillin monotherapy: Add or substitute a macrolide 6
- For non-severe pneumonia on combination therapy: Switch to a respiratory fluoroquinolone 6
- For severe pneumonia not responding to combination therapy: Consider adding rifampicin 6
Critical Clinical Pitfalls to Avoid
- Never delay antibiotic administration beyond 8 hours in hospitalized patients—this significantly increases mortality 1, 2
- Never use macrolide monotherapy in areas where pneumococcal macrolide resistance exceeds 25% 1, 2
- Never use cefepime, piperacillin-tazobactam, or carbapenems as first-line therapy without documented risk factors for resistant organisms 1
- Always obtain blood and sputum cultures before initiating antibiotics in all hospitalized patients 1
- Avoid extending therapy beyond 7 days in responding patients without specific indications—this increases antimicrobial resistance risk 1