Antibiotic Selection and Dosing for Bilateral Pneumonia with Gastrointestinal Infection
Recommended Empiric Regimen
For a patient with bilateral pneumonia and gastrointestinal infection, initiate combination therapy with cefepime 2 g IV every 8 hours PLUS metronidazole 500 mg IV every 6-8 hours, with consideration for adding vancomycin 15 mg/kg IV every 8-12 hours if MRSA risk factors are present. 1, 2
Pneumonia Component
Initial Antibiotic Selection
Cefepime is the preferred beta-lactam for moderate to severe pneumonia, dosed at 1-2 g IV every 8-12 hours for 10 days. 1, 2 For Pseudomonas aeruginosa coverage specifically, use the higher dose of 2 g IV every 8 hours. 1, 2
Alternative antipseudomonal agents include:
- Piperacillin-tazobactam 4.5 g IV every 6 hours 1
- Ceftazidime 2 g IV every 8 hours 1
- Meropenem 1 g IV every 8 hours 1
- Imipenem 500 mg IV every 6 hours or 1 g IV every 8 hours 1
MRSA Coverage Decision
Add vancomycin 15 mg/kg IV every 8-12 hours (targeting trough levels of 15-20 mg/mL) if the patient has received IV antibiotics in the prior 90 days, is in a unit where MRSA prevalence exceeds 20%, or has septic shock. 1 Consider a loading dose of 25-30 mg/kg IV × 1 for severe illness. 1
Linezolid 600 mg IV every 12 hours is an alternative to vancomycin with comparable efficacy. 1
Important caveat: Standard vancomycin dosing of 1 g IV every 12 hours is inadequate for critically ill patients with pneumonia and will not achieve therapeutic trough levels of 15-20 mg/L. 3 Doses of at least 1 g IV every 8 hours are required in this population. 3
Gastrointestinal Infection Component
Complicated Intra-Abdominal Coverage
For the gastrointestinal component, cefepime 2 g IV every 8-12 hours MUST be combined with metronidazole 500 mg IV every 6-8 hours to provide anaerobic coverage for 7-10 days. 1, 2
Alternative regimens for complicated intra-abdominal infections include:
- Piperacillin-tazobactam 3.375 g IV every 6 hours (provides both aerobic and anaerobic coverage without additional metronidazole) 1
- Meropenem 1 g IV every 8 hours (monotherapy, no metronidazole needed) 1
- Imipenem/cilastatin 500 mg IV every 6 hours or 1 g IV every 8 hours (monotherapy) 1
For carbapenem-resistant Enterobacterales (CRE) in the GI tract, use ceftazidime/avibactam 2.5 g IV every 8 hours PLUS metronidazole 500 mg IV every 6 hours for 5-7 days. 1
Combination Therapy Considerations
Nephrotoxicity Warning
Avoid combining vancomycin with piperacillin-tazobactam due to significantly increased nephrotoxicity risk. 4 Patients receiving vancomycin plus piperacillin-tazobactam are 6.7 times more likely to develop acute kidney injury compared to vancomycin plus cefepime or meropenem. 4 The incidence of acute kidney injury is 29.8% with vancomycin-piperacillin/tazobactam versus 8.8% with vancomycin-cefepime or vancomycin-meropenem. 4
Dual Coverage for High-Risk Patients
If the patient has structural lung disease (bronchiectasis, cystic fibrosis), received IV antibiotics in the prior 90 days, or has septic shock, add a second antipseudomonal agent from a different class. 1 Options include:
- Aminoglycosides: Amikacin 15-20 mg/kg IV daily, gentamicin 5-7 mg/kg IV daily, or tobramycin 5-7 mg/kg IV daily 1
- Fluoroquinolones: Levofloxacin 750 mg IV daily or ciprofloxacin 400 mg IV every 8 hours 1
Avoid using two beta-lactams together. 1
Duration of Therapy
- Pneumonia: 10-14 days for hospital-acquired/ventilator-associated pneumonia; 7-10 days for community-acquired pneumonia 1
- Complicated intra-abdominal infection: 4-7 days if adequate source control achieved; 7-10 days if source control difficult 1
Renal Dose Adjustments
For cefepime in patients with CrCL 30-60 mL/min, reduce to 2 g IV every 24 hours; for CrCL 11-29 mL/min, reduce to 1 g IV every 24 hours. 2
For vancomycin, monitor trough levels and adjust dosing to maintain levels of 15-20 mg/mL. 1