Antibiotic Regimen for Immunosuppressed Pneumonia with Penicillin Allergy

Introduction to Antibiotic Regimens

The Centers for Disease Control and Prevention recommends using a respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) plus vancomycin 15 mg/kg IV q8-12h (targeting trough 15-20 mg/mL) or linezolid 600 mg IV q12h for MRSA coverage in immunosuppressed patients with pneumonia and penicillin allergy 1, 2

For non-ICU patients with community-acquired pneumonia (CAP) and penicillin allergy, the Infectious Diseases Society of America recommends using a respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) as monotherapy 1
For ICU patients with CAP and penicillin allergy, the Infectious Diseases Society of America recommends using aztreonam 2 g IV q8h plus a respiratory fluoroquinolone (levofloxacin 750 mg IV daily or moxifloxacin 400 mg IV daily) 1
For high-risk patients with hospital-acquired pneumonia (HAP) and penicillin allergy, the Infectious Diseases Society of America recommends using two antipseudomonal agents from different classes, including aztreonam 2 g IV q8h and levofloxacin 750 mg IV daily or ciprofloxacin 400 mg IV q8h, plus vancomycin 15 mg/kg IV q8-12h or linezolid 600 mg IV q12h for MRSA coverage 2, 3, 5

Aztreonam is the only β-lactam that is safe in severe penicillin allergy because it lacks cross-reactivity with penicillins and cephalosporins, according to the Infectious Diseases Society of America 2, 3, 5
When aztreonam replaces a β-lactam in the empiric regimen, the Infectious Diseases Society of America recommends adding specific MSSA coverage, typically with levofloxacin or another fluoroquinolone 2, 3, 5

The Infectious Diseases Society of America recommends adding vancomycin or linezolid when any of the following are present: IV antibiotic use within the prior 90 days, unit prevalence of MRSA among S. aureus isolates >20% or unknown, prior MRSA colonization or infection, or high risk of mortality (ventilatory support, septic shock) 2, 3, 5

The Infectious Diseases Society of America recommends the following doses: levofloxacin 750 mg IV daily, aztreonam 2 g IV q8h, vancomycin 15 mg/kg IV q8-12h targeting trough 15-20 mg/mL, and linezolid 600 mg IV q12h 1, 2, 3
The Infectious Diseases Society of America recommends the following durations: 5-7 days for high-dose levofloxacin, 7-10 days for standard regimens, and 10-14 days for severe pneumonia with complications 7

The Centers for Disease Control and Prevention recommends never using macrolide monotherapy in immunosuppressed patients due to high pneumococcal resistance rates 1
The Centers for Disease Control and Prevention recommends avoiding using only aztreonam without adding MSSA coverage, as aztreonam lacks gram-positive activity 2, 3, 5