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Difficulty: MediumInfectious Diseases

During multidisciplinary rounds in the surgical intensive care unit, the team evaluates the antimicrobial regimen for a 54-year-old man. The patient underwent an exploratory laparotomy 8 days ago for a perforated viscus. On his fifth postoperative day, he developed a temperature of 38.9°C (102.0°F) and tachycardia. His right internal jugular central venous catheter, which had been placed preoperatively, was removed, and blood cultures were drawn from peripheral veins and the catheter before removal. Empiric therapy with intravenous vancomycin and cefepime was initiated. Today, the microbiology laboratory reports that two out of two blood culture sets are growing Staphylococcus aureus. The susceptibility panel indicates resistance to penicillin and ampicillin, but susceptibility to oxacillin, cefazolin, vancomycin, and daptomycin. The patient has no known drug allergies. His current temperature is 37.2°C (99.0°F), blood pressure is 128/82 mmHg, and pulse is 82/min. Which of the following is the most appropriate next step in the pharmacologic management of this patient?

  1. A
    Discontinue vancomycin and cefepime; start intravenous daptomycin
  2. B
    Discontinue cefepime; continue intravenous vancomycin
  3. Discontinue vancomycin and cefepime; start intravenous cefazolinAnswer
  4. D
    Continue both intravenous vancomycin and cefepime
  5. E
    Discontinue vancomycin and cefepime; start oral linezolid

Answer

Discontinue the empiric broad-spectrum antibiotics and transition to intravenous cefazolin for targeted MSSA therapy.
The patient has Methicillin-Susceptible Staphylococcus aureus (MSSA) bacteremia, indicated by susceptibility to oxacillin. The cornerstone of antimicrobial stewardship is de-escalating empiric therapy to the narrowest spectrum, most effective agent once culture and susceptibility data are available. For MSSA bacteremia, intravenous anti-staphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the drugs of choice. Extensive clinical data demonstrate that beta-lactams are superior to vancomycin for clearing MSSA bacteremia, resulting in lower rates of clinical failure, relapse, and mortality. Therefore, discontinuing the empiric vancomycin and cefepime and initiating intravenous cefazolin is the most appropriate next step.

Step-by-Step Solution

1
Interpret the blood culture and susceptibility results.
The pathogen is oxacillin-susceptible Staphylococcus aureus (MSSA).
Oxacillin susceptibility defines the isolate as MSSA, which changes the preferred treatment algorithm.
2
Evaluate the current empiric antimicrobial regimen (vancomycin and cefepime).
The current regimen is too broad and vancomycin is suboptimal for MSSA.
Antimicrobial stewardship dictates de-escalating to the narrowest effective agent. Beta-lactams are superior to vancomycin for MSSA.
3
Select the optimal targeted therapy.
Intravenous cefazolin (or nafcillin/oxacillin) is selected.
Cefazolin provides potent, narrow-spectrum bactericidal activity against MSSA with an excellent safety profile, making it the standard of care.

Key Concept

In patients with Methicillin-Susceptible Staphylococcus aureus (MSSA) bacteremia, targeted therapy with an intravenous anti-staphylococcal beta-lactam (e.g., cefazolin, nafcillin) is superior to vancomycin, leading to improved clinical outcomes and reduced mortality.
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Infectious Diseases

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