IV Antibiotics for Hospital-Acquired Pneumonia in Patients with PCN Allergy
For patients with Hospital-Acquired Pneumonia (HAP) and penicillin allergy, aztreonam plus either vancomycin or linezolid is the recommended IV antibiotic regimen, with specific therapy determined by risk factors for mortality and MRSA. 1
Antibiotic Selection Algorithm Based on Risk Stratification
Low Mortality Risk, No MRSA Risk Factors
- First-line option: Aztreonam 2g IV q8h
- Alternative options:
- Levofloxacin 750mg IV daily
- Ciprofloxacin 400mg IV q8h
Low Mortality Risk with MRSA Risk Factors
- Base therapy: Aztreonam 2g IV q8h
- Plus one of the following for MRSA coverage:
- Vancomycin 15mg/kg IV q8-12h (target trough 15-20mg/mL)
- Linezolid 600mg IV q12h
High Mortality Risk
- Two antipseudomonal agents (avoid double β-lactams):
- Aztreonam 2g IV q8h
- Plus one of:
- Levofloxacin 750mg IV daily
- Ciprofloxacin 400mg IV q8h
- Amikacin 15-20mg/kg IV daily
- Gentamicin 5-7mg/kg IV daily
- Tobramycin 5-7mg/kg IV daily
- Plus MRSA coverage:
- Vancomycin 15mg/kg IV q8-12h (target trough 15-20mg/mL)
- OR Linezolid 600mg IV q12h
Risk Factor Assessment
MRSA Risk Factors
- IV antibiotic treatment during prior 90 days
- Treatment in a unit where MRSA prevalence among S. aureus is >20% or unknown
- Prior MRSA detection by culture or screening
Mortality Risk Factors
- Need for ventilatory support due to pneumonia
- Septic shock
Special Considerations
Gram-negative Coverage
Aztreonam is particularly valuable in penicillin-allergic patients as it provides excellent gram-negative coverage (including Pseudomonas) without cross-reactivity with penicillin allergy 1. The 2016 IDSA/ATS guidelines specifically state that "if patient has severe penicillin allergy and aztreonam is going to be used instead of any β-lactam–based antibiotic, include coverage for MSSA." 1
MRSA Coverage
For MRSA coverage, the guidelines strongly recommend vancomycin or linezolid rather than alternative antibiotics 1. Linezolid may be particularly advantageous in HAP as it has shown potential benefits in hospital-acquired pneumonia compared to vancomycin 2.
Duration of Therapy
Treatment should typically continue for 7 days, with adjustment based on clinical response.
Important Caveats
- Ensure MSSA coverage is included if not using MRSA coverage
- Avoid double β-lactam therapy when selecting combination regimens
- Consider local antibiogram data to guide empiric therapy choices
- De-escalate therapy once culture results are available (typically 48-72 hours)
- For patients on mechanical ventilation, combination therapy is particularly important due to higher mortality risk 3
This approach ensures appropriate antimicrobial coverage while avoiding β-lactam antibiotics in penicillin-allergic patients, thus reducing the risk of allergic reactions while optimizing outcomes for HAP.