What empiric antibiotic regimen should be used for an adult inpatient with pneumonia and no known drug allergies?

Empiric Antibiotic Regimen for Adult Inpatient Pneumonia

Community-Acquired Pneumonia (CAP) – Non-ICU

For hospitalized adults with community-acquired pneumonia and no drug allergies, use a beta-lactam (ceftriaxone 1-2g IV daily, ampicillin-sulbactam 1.5-3g IV every 6 hours, or cefuroxime) plus a macrolide (azithromycin 500mg IV daily or clarithromycin), OR use a respiratory fluoroquinolone alone (levofloxacin 750mg IV daily or moxifloxacin 400mg IV daily). 1, 2, 3

Risk Stratification for Broader Coverage

Add MRSA coverage (vancomycin 15mg/kg IV every 8-12 hours targeting trough 15-20 mg/L OR linezolid 600mg IV every 12 hours) if any of the following are present: 1, 2, 3

• Prior IV antibiotic use within 90 days
• Healthcare setting where MRSA prevalence among S. aureus isolates exceeds 20% or is unknown
• Prior MRSA colonization or infection
• Septic shock requiring vasopressors

Add antipseudomonal coverage (piperacillin-tazobactam 4.5g IV every 6 hours, cefepime 2g IV every 8 hours, or meropenem 1g IV every 8 hours) if: 1, 2, 3

• Structural lung disease (bronchiectasis, cystic fibrosis)
• Recent IV antibiotic use within 90 days
• Healthcare-associated infection

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Hospital-Acquired Pneumonia (HAP) / Ventilator-Associated Pneumonia (VAP)

For HAP/VAP without MDR risk factors, use piperacillin-tazobactam 4.5g IV every 6 hours OR cefepime 2g IV every 8 hours as monotherapy. 1, 3

MDR Risk Factor Assessment

Use triple-drug combination therapy if ANY of the following MDR risk factors are present: 1, 3, 4

• Prior IV antibiotic use within 90 days
• ≥5 days of hospitalization prior to pneumonia onset
• Septic shock at time of presentation
• ARDS preceding pneumonia
• Acute renal replacement therapy prior to onset

Triple-Drug Regimen for MDR Risk

Combine: 1, 3

1. Antipseudomonal beta-lactam: Piperacillin-tazobactam 4.5g IV every 6 hours, cefepime 2g IV every 8 hours, ceftazidime 2g IV every 8 hours, meropenem 1g IV every 8 hours, OR imipenem 500mg IV every 6 hours
2. Second antipseudomonal agent from different class: Ciprofloxacin 400mg IV every 8 hours, levofloxacin 750mg IV daily, OR amikacin 15-20mg/kg IV daily
3. MRSA coverage: Vancomycin 15mg/kg IV every 8-12 hours (target trough 15-20 mg/L) OR linezolid 600mg IV every 12 hours

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Aspiration Pneumonia

Do NOT routinely add specific anaerobic coverage (metronidazole) unless lung abscess or empyema is documented. 2, 3 Modern evidence shows gram-negative pathogens and S. aureus predominate, not pure anaerobes. 2

For community-acquired aspiration pneumonia (non-ICU): 2, 3

• Ampicillin-sulbactam 1.5-3g IV every 6 hours OR amoxicillin-clavulanate 1-2g IV every 8 hours
• Alternative: Moxifloxacin 400mg IV daily (provides adequate anaerobic coverage)

For severe aspiration pneumonia or ICU patients: 2, 3

• Piperacillin-tazobactam 4.5g IV every 6 hours PLUS azithromycin 500mg IV daily OR levofloxacin 750mg IV daily
• Add MRSA and antipseudomonal coverage based on risk factors above

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Nursing Home Residents

Nursing home patients have higher rates of resistant gram-negatives and MRSA. 1 Use broader initial coverage: 1, 2

• Piperacillin-tazobactam 4.5g IV every 6 hours OR respiratory fluoroquinolone (levofloxacin 750mg IV daily or moxifloxacin 400mg IV daily)
• Consider adding vancomycin if local MRSA prevalence >20%

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Treatment Duration and De-escalation

Standard duration is 5-8 days for responding patients; do not exceed 8 days in those with adequate clinical response. 2, 3 Monitor response using: 2

• Temperature ≤37.8°C
• Heart rate ≤100 bpm
• Respiratory rate ≤24 breaths/min
• Systolic BP ≥90 mmHg

De-escalate therapy at 48-72 hours based on culture results and clinical response. 1, 3 Switch to oral therapy when hemodynamically stable, improving clinically, and able to tolerate oral intake. 2, 3

Measure C-reactive protein on days 1 and 3-4 to assess response, especially in patients with unfavorable clinical parameters. 2

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Critical Pitfalls to Avoid

Never use ciprofloxacin alone for pneumonia – it has poor activity against S. pneumoniae and lacks anaerobic coverage. 2 Use moxifloxacin or levofloxacin 750mg instead. 2

Do not delay antibiotics waiting for cultures – delay in appropriate therapy is consistently associated with increased mortality. 2, 5 Start empiric therapy within the first hour. 2

Do not assume all aspiration requires anaerobic coverage – this increases C. difficile risk without mortality benefit. 2 Add metronidazole only for documented abscess or empyema. 2, 3

Tailor empiric regimens to local antibiogram data – institutional resistance patterns should guide MRSA and Pseudomonas coverage thresholds. 1, 3