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Difficulty: MediumInfectious Diseases

A critical care physician is reviewing the microbiological data for a patient admitted with a severe burn injury. One week into the hospitalization, the patient developed a new-onset fever of 39.4∘C39.4^\circ\text{C} (102.9∘F102.9^\circ\text{F}) and hypotension requiring vasopressor support. Blood cultures were obtained from a central venous catheter and a peripheral vein, and empiric antimicrobial therapy with intravenous vancomycin, cefepime, and gentamicin was instituted.

Today, both sets of blood cultures are positive for *Klebsiella pneumoniae*. The microbiology laboratory reports that the isolate is susceptible to ceftriaxone, cefepime, piperacillin-tazobactam, and meropenem, but resistant to ampicillin. The patient's clinical status has stabilized significantly; the fever has resolved, and vasopressor support was discontinued yesterday. Based on the principles of antimicrobial stewardship, which of the following is the most appropriate modification to this patient's pharmacologic regimen?

  1. A
    Discontinue vancomycin and gentamicin, and continue intravenous cefepime
  2. B
    Discontinue all current antibiotics and initiate intravenous meropenem
  3. Discontinue all current antibiotics and initiate intravenous ceftriaxoneAnswer
  4. D
    Continue intravenous vancomycin, cefepime, and gentamicin
  5. E
    Discontinue vancomycin and gentamicin, and initiate intravenous piperacillin-tazobactam

Answer

The most appropriate next step is to discontinue the broad-spectrum empiric regimen (vancomycin, cefepime, and gentamicin) and transition to intravenous ceftriaxone, which provides targeted, narrow-spectrum coverage for the susceptible pathogen.
This patient's blood cultures have finalized, revealing *Klebsiella pneumoniae*. Susceptibility testing indicates the organism is vulnerable to ceftriaxone, a third-generation cephalosporin. Once a pathogen is identified and susceptibilities are known, the core principle of antimicrobial stewardship dictates de-escalating from empiric broad-spectrum therapy to a targeted, narrower-spectrum agent. Ceftriaxone is highly efficacious for susceptible *Klebsiella* bacteremia, possesses a favorable side-effect profile, and lacks anti-pseudomonal activity, making it the ideal narrow-spectrum choice to replace the unnecessarily broad vancomycin, cefepime, and gentamicin regimen.

Step-by-Step Solution

1
Identify the infecting pathogen and its susceptibilities.
The patient has a bloodstream infection caused by Klebsiella pneumoniae that is susceptible to ceftriaxone, among other broader-spectrum agents.
Pathogen identification and susceptibility testing are required to transition from empiric to definitive therapy.
2
Evaluate the current empiric antibiotic regimen.
The patient is receiving vancomycin (anti-MRSA), cefepime (anti-pseudomonal), and gentamicin (additional Gram-negative coverage), which was appropriate empirically for a critically ill burn patient.
Empiric therapy must cover likely resistant organisms until cultures finalize and the patient stabilizes.
3
Apply antimicrobial stewardship principles to select definitive therapy.
Therapy should be de-escalated by discontinuing unnecessary MRSA and pseudomonal coverage. Ceftriaxone provides the narrowest effective coverage for this specific isolate.
De-escalation minimizes toxicity (e.g., nephrotoxicity from vancomycin and gentamicin) and prevents the emergence of antimicrobial resistance.

Key Concept

In patients with culture-confirmed Gram-negative bacteremia, empiric broad-spectrum antimicrobial therapy should be de-escalated to the narrowest-spectrum agent demonstrated to be effective by susceptibility testing (e.g., a third-generation cephalosporin for susceptible Enterobacteriaceae).
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Infectious Diseases

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