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Difficulty: MediumInfectious Diseases

A physician is reviewing the microbiological data for a patient in the intensive care unit. The 58-year-old female patient was admitted 6 days ago for severe acute pancreatitis and required immediate endotracheal intubation and mechanical ventilation. On hospital day 4, she developed a temperature of 38.6°C (101.5°F), an increased volume of purulent endotracheal secretions, and worsening oxygenation. A chest radiograph demonstrated a new left lower lobe consolidation. A bronchoalveolar lavage was performed, and the patient was empirically started on intravenous vancomycin and piperacillin-tazobactam for suspected ventilator-associated pneumonia.

Today, the patient's temperature is 37.3°C (99.1°F) and her oxygen requirements have decreased. The bronchoalveolar lavage quantitative culture grows *Escherichia coli* at >105>10^5 colony-forming units/mL. Blood cultures show no growth after 48 hours. The antimicrobial susceptibility profile for the respiratory isolate is as follows:

AntimicrobialSusceptibility
AmpicillinResistant
CefepimeSusceptible
CeftriaxoneSusceptible
MeropenemSusceptible
Piperacillin-tazobactamSusceptible

Based on the culture and susceptibility results, which of the following is the most appropriate next step in the pharmacologic management of this patient?

  1. Discontinue vancomycin and piperacillin-tazobactam; initiate intravenous ceftriaxoneAnswer
  2. B
    Discontinue vancomycin; continue intravenous piperacillin-tazobactam
  3. C
    Continue both intravenous vancomycin and piperacillin-tazobactam
  4. D
    Discontinue vancomycin and piperacillin-tazobactam; initiate intravenous meropenem
  5. E
    Discontinue vancomycin and piperacillin-tazobactam; initiate intravenous cefepime

Answer

Discontinue vancomycin and piperacillin-tazobactam; initiate intravenous ceftriaxone
The correct answer reflects the core principle of antimicrobial stewardship: de-escalation. The patient developed ventilator-associated pneumonia and was appropriately placed on a broad-spectrum empiric regimen (vancomycin and piperacillin-tazobactam). Upon receiving quantitative culture data isolating *Escherichia coli* that is susceptible to ceftriaxone, the clinical imperative is to narrow the spectrum of therapy. Ceftriaxone is a third-generation cephalosporin that provides excellent targeted coverage for this isolate. Discontinuing both vancomycin (as there is no MRSA) and piperacillin-tazobactam (to avoid unnecessary antipseudomonal and anaerobic coverage) minimizes toxicity and prevents the emergence of resistant flora.

Step-by-Step Solution

1
Evaluate the clinical scenario and the diagnosis.
The patient developed ventilator-associated pneumonia (VAP) and was correctly started on empiric broad-spectrum antibiotics (vancomycin for MRSA, piperacillin-tazobactam for Pseudomonas and other Gram-negatives).
Empiric therapy must cover the most likely and dangerous pathogens in the ICU setting until cultures return.
2
Interpret the microbiological culture and susceptibility data.
The culture grew a single pathogen: Escherichia coli. It is resistant to ampicillin but susceptible to ceftriaxone, cefepime, meropenem, and piperacillin-tazobactam. Blood cultures are negative.
Microbiological data allows for the transition from empiric to targeted therapy.
3
Apply antimicrobial stewardship principles to select the definitive therapy.
De-escalate to ceftriaxone.
Once susceptibilities are known, therapy should be narrowed to the most targeted agent. Ceftriaxone is a third-generation cephalosporin that adequately treats the E. coli without providing unnecessary antipseudomonal (piperacillin-tazobactam, cefepime, meropenem), anaerobic (piperacillin-tazobactam, meropenem), or anti-MRSA (vancomycin) coverage.

Key Concept

Antimicrobial De-escalation in Hospital-Acquired Infections
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Topics

Infectious Diseases

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