Community-Acquired Pneumonia (CAP) Initial Antibiotic Treatment Protocol
Outpatient Treatment (No Hospitalization Required)
For previously healthy adults without comorbidities, amoxicillin 1 g orally three times daily for 5-7 days is the preferred first-line therapy. 1
Healthy Adults Without Comorbidities
- First-line: Amoxicillin 1 g PO three times daily for 5-7 days 1, 2
- Alternative: Doxycycline 100 mg PO twice daily for 5-7 days 1
- Macrolides (azithromycin 500 mg day 1, then 250 mg daily for days 2-5; or clarithromycin 500 mg twice daily) should only be used in areas where pneumococcal macrolide resistance is documented <25% 1, 3
Adults With Comorbidities (COPD, diabetes, heart/liver/renal disease, malignancy)
- Combination therapy: β-lactam (amoxicillin-clavulanate 875/125 mg twice daily, cefpodoxime, or cefuroxime) PLUS macrolide (azithromycin or clarithromycin) OR doxycycline 100 mg twice daily 1
- Alternative monotherapy: Respiratory fluoroquinolone (levofloxacin 750 mg daily, moxifloxacin 400 mg daily, or gemifloxacin 320 mg daily) 1, 4
Critical pitfall: Never use macrolide monotherapy in areas where pneumococcal resistance exceeds 25%—this leads to treatment failure. 1
Hospitalized Patients (Non-ICU)
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, 5
Standard Regimens (Two Equally Effective Options)
- β-lactam + macrolide combination: Ceftriaxone 1-2 g IV daily PLUS azithromycin 500 mg daily 1, 5
- Alternative β-lactams: Cefotaxime 1-2 g IV every 8 hours OR ampicillin-sulbactam 3 g IV every 6 hours 1
- Respiratory fluoroquinolone monotherapy: Levofloxacin 750 mg IV daily OR moxifloxacin 400 mg IV daily 1, 4
Penicillin-Allergic Patients
- Preferred: Respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 1
- Alternative: Aztreonam 2 g IV every 8 hours PLUS azithromycin 500 mg IV daily 1
Timing of First Dose
Administer the first antibiotic dose in the emergency department immediately upon diagnosis—delayed administration beyond 8 hours increases 30-day mortality by 20-30%. 6, 1
Severe CAP Requiring ICU Admission
For ICU patients with severe CAP, mandatory combination therapy with ceftriaxone 2 g IV daily PLUS either azithromycin 500 mg IV daily OR a respiratory fluoroquinolone is required. 1, 5
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 either:
Critical principle: Monotherapy is inadequate for severe disease—combination therapy is mandatory for all ICU patients. 1
Special Pathogen Coverage
Risk Factors for Pseudomonas aeruginosa
Add antipseudomonal coverage only when these risk factors are present: 1
- Structural lung disease (bronchiectasis)
- Recent hospitalization with IV antibiotics within 90 days
- Prior respiratory isolation of P. aeruginosa
Antipseudomonal regimen: 1
- 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) for dual antipseudomonal coverage
Risk Factors for MRSA
Add MRSA coverage only when these risk factors are present: 1
- Prior MRSA infection or colonization
- Recent hospitalization with IV antibiotics
- Post-influenza pneumonia
- Cavitary infiltrates on imaging
MRSA regimen: Vancomycin 15 mg/kg IV every 8-12 hours (target trough 15-20 mg/mL) OR linezolid 600 mg IV every 12 hours added to base regimen 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, 5
Standard Duration
- Uncomplicated CAP: 5-7 days total 1, 5
- Clinical stability criteria before discontinuation: 1
- Temperature ≤37.8°C
- Heart rate ≤100 beats/min
- Respiratory rate ≤24 breaths/min
- Systolic blood pressure ≥90 mmHg
- Oxygen saturation ≥90% on room air
- Able to maintain oral intake
- Normal mental status
Extended Duration (14-21 days) Required For:
Transition from IV 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. 1
Oral Step-Down Options
- From ceftriaxone + azithromycin: Amoxicillin 1 g PO three times daily PLUS azithromycin 500 mg PO daily 1
- From fluoroquinolone IV: Continue same fluoroquinolone orally (levofloxacin 750 mg PO daily or moxifloxacin 400 mg PO daily) 1, 4
Diagnostic Testing for Hospitalized Patients
Obtain blood cultures and sputum Gram stain/culture before initiating antibiotics in ALL hospitalized patients. 1
Recommended Testing
- Blood cultures (two sets) 6, 1
- Sputum Gram stain and culture (if adequate specimen available) 6, 1
- COVID-19 and influenza testing when these viruses are common in the community 5
- Urinary antigen testing for Legionella pneumophila serogroup 1 in severe CAP or ICU patients 1
Critical Pitfalls to Avoid
- Never delay antibiotics: Administration beyond 8 hours increases mortality by 20-30% in hospitalized patients 6, 1
- Never use macrolide monotherapy for hospitalized patients: Provides inadequate coverage for typical bacterial pathogens like S. pneumoniae 1
- Never use macrolides in high-resistance areas: Avoid when local pneumococcal macrolide resistance exceeds 25% 1
- Never use monotherapy in ICU patients: Combination therapy is mandatory for severe disease 1
- Never add broad-spectrum coverage without risk factors: Only add antipseudomonal or MRSA coverage when specific risk factors are documented 1
- Never extend therapy beyond 7-8 days without indication: Longer courses increase resistance risk without improving outcomes 1