What are the recommended IV antibiotics for pneumonia?

IV Antibiotic Selection for Pneumonia

For hospital-acquired pneumonia (HAP) and ventilator-associated pneumonia (VAP), start with piperacillin-tazobactam 4.5g IV every 6 hours as the backbone regimen, adding vancomycin or linezolid for MRSA coverage and a second antipseudomonal agent (fluoroquinolone or aminoglycoside) based on mortality risk factors and local resistance patterns. 1

Risk Stratification Framework

The choice of IV antibiotics depends critically on two factors: mortality risk and MRSA risk factors. 1

High Mortality Risk Factors:

• Need for ventilatory support due to pneumonia 1, 2
• Septic shock at time of presentation 1
• ARDS preceding VAP 1
• Acute renal replacement therapy prior to VAP onset 1

MRSA Risk Factors:

• Prior IV antibiotic use within 90 days 1
• Hospitalization in a unit where >20% of S. aureus isolates are methicillin-resistant 1
• Unknown MRSA prevalence 1
• Five or more days of hospitalization prior to VAP 1

Treatment Algorithm by Clinical Scenario

For Ventilator-Associated Pneumonia (VAP):

Triple therapy is standard: Choose one agent from each category below 1:

MRSA Coverage (Column A):

• Vancomycin 15 mg/kg IV q8-12h (consider loading dose 25-30 mg/kg for severe illness, target trough 15-20 mg/mL) 1
• OR Linezolid 600 mg IV q12h 1

Primary Antipseudomonal β-Lactam (Column B):

• Piperacillin-tazobactam 4.5g IV q6h (preferred first-line) 1, 3
• OR Cefepime 2g IV q8h 1
• OR Ceftazidime 2g IV q8h 1
• OR Imipenem 500 mg IV q6h 1
• OR Meropenem 1g IV q8h 1

Second Antipseudomonal Agent (Column C):

• Ciprofloxacin 400 mg IV q8h 1
• OR Levofloxacin 750 mg IV daily 1
• OR Amikacin 15-20 mg/kg IV q24h 1
• OR Gentamicin 5-7 mg/kg IV q24h 1
• OR Tobramycin 5-7 mg/kg IV q24h 1

For Hospital-Acquired Pneumonia (Non-Ventilated):

Low mortality risk WITHOUT MRSA risk factors:

• Monotherapy with piperacillin-tazobactam 4.5g IV q6h 1, 2
• OR Cefepime 2g IV q8h 1
• OR Levofloxacin 750 mg IV daily 1
• OR Imipenem 500 mg IV q6h 1
• OR Meropenem 1g IV q8h 1

Low mortality risk WITH MRSA risk factors:

• Same gram-negative coverage as above PLUS 1
• Vancomycin 15 mg/kg IV q8-12h OR Linezolid 600 mg IV q12h 1, 2

High mortality risk OR recent IV antibiotics (within 90 days):

• Dual antipseudomonal coverage: Choose TWO agents from different classes (avoid two β-lactams) 1, 4
• Piperacillin-tazobactam 4.5g IV q6h OR Cefepime/Ceftazidime 2g IV q8h OR Carbapenem 1
• PLUS Fluoroquinolone (ciprofloxacin 400mg IV q8h or levofloxacin 750mg IV daily) OR Aminoglycoside 1
• PLUS MRSA coverage (vancomycin or linezolid) 1

For Aspiration Pneumonia:

Piperacillin-tazobactam 4.5g IV q6h is the preferred first-line agent because it provides inherent anaerobic coverage required for aspiration pneumonia. 2

• Low risk: Piperacillin-tazobactam monotherapy 2
• High risk or ventilated: Add second antipseudomonal agent and MRSA coverage as per HAP/VAP guidelines 2

Critical Dosing Considerations

Renal Impairment Adjustments:

For piperacillin-tazobactam in patients with renal dysfunction 3:

• CrCl >40 mL/min: Standard dosing (4.5g q6h for nosocomial pneumonia) 3
• CrCl 20-40 mL/min: 3.375g q6h for nosocomial pneumonia 3
• CrCl <20 mL/min: 2.25g q6h 3
• Hemodialysis: 2.25g q8h plus 0.75g after each dialysis session 3

Infusion Duration:

All IV antibiotics should be infused over 30 minutes to optimize pharmacokinetics and minimize adverse effects. 1, 3

Common Pitfalls to Avoid

Never use aztreonam as monotherapy - it lacks gram-positive activity and requires addition of MRSA coverage (vancomycin or linezolid). 1, 2

Avoid aminoglycoside monotherapy - meta-analyses show lower clinical response rates compared to other regimens, though mortality is similar. 1

Do not use two β-lactams together - they have overlapping mechanisms and provide no additional benefit. 1

Polymyxins (colistin, polymyxin B) should be reserved for settings with high multidrug resistance prevalence and local expertise, not for routine empiric therapy. 1

For confirmed MSSA (not MRSA), narrow therapy to oxacillin, nafcillin, or cefazolin rather than continuing broad-spectrum agents. 1, 4

Duration of Therapy

• HAP (non-VAP): 7-10 days 3
• Nosocomial pneumonia/VAP: 7-14 days 3
• Aspiration pneumonia: 5-7 days if afebrile for 48 hours and clinically stable 2

Continue aminoglycoside therapy only in patients from whom P. aeruginosa is isolated on culture results. 3

De-escalation Strategy

Once culture results return, narrow antibiotic spectrum based on susceptibilities to reduce C. difficile risk, adverse effects, and resistance development. 1 If MRSA was covered empirically but not isolated, discontinue vancomycin or linezolid. 1 If only susceptible gram-negative organisms are identified, consider switching from dual to single antipseudomonal coverage. 1