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Difficulty: MediumInfectious Diseases

A 71-year-old male is currently on the medical ward receiving treatment for a severe skin and soft tissue infection complicated by bloodstream invasion. He was admitted 72 hours ago with marked swelling, warmth, and purulence of his left forearm following a minor abrasion. At the time of admission, he was febrile and hypotensive, prompting the initiation of broad-spectrum coverage with intravenous vancomycin and cefepime. He has since hemodynamically stabilized and is now afebrile. The microbiology laboratory reports that both sets of blood cultures obtained at admission are positive for Staphylococcus aureus. Susceptibility testing reveals the organism is susceptible to oxacillin, cefazolin, clindamycin, and vancomycin, but resistant to penicillin. Which of the following is the most appropriate modification to his antimicrobial regimen?

  1. Change the regimen to intravenous cefazolin.Answer
  2. B
    Maintain the current regimen of vancomycin and cefepime.
  3. C
    Stop cefepime and continue vancomycin monotherapy.
  4. D
    Stop vancomycin and continue cefepime monotherapy.
  5. E
    Change the regimen to oral clindamycin.

Answer

Change the regimen to intravenous cefazolin.
The patient's blood cultures are positive for methicillin-susceptible Staphylococcus aureus (MSSA). The current standard of care for MSSA bacteremia involves targeted intravenous therapy with a narrow-spectrum beta-lactam agent, such as a first-generation cephalosporin (cefazolin) or an antistaphylococcal penicillin (nafcillin, oxacillin). These agents have been shown to be clinically superior to vancomycin for MSSA infections, leading to faster clearance of bacteremia and improved clinical outcomes. Therefore, applying the principles of antimicrobial stewardship, the most appropriate next step is to discontinue the overly broad-spectrum empiric regimen (vancomycin and cefepime) and transition to definitive therapy with intravenous cefazolin.

Step-by-Step Solution

1
Identify the infecting organism and its resistance profile from the blood culture results.
The organism is methicillin-susceptible Staphylococcus aureus (MSSA).
Determining the specific pathogen and susceptibilities is required to narrow empiric antibiotic therapy appropriately.
2
Evaluate the current empiric antibiotic regimen against the targeted pathogen.
The patient is on vancomycin and cefepime, which are too broad and not the optimal targeted therapy for MSSA.
Prolonged use of broad-spectrum agents promotes resistance, and vancomycin is clinically inferior to anti-staphylococcal beta-lactams for MSSA.
3
Select the most appropriate definitive therapy for MSSA bacteremia.
Intravenous cefazolin is chosen as it provides targeted, superior bactericidal activity against MSSA.
Antimicrobial stewardship guidelines strongly recommend de-escalating to narrow-spectrum beta-lactams like cefazolin, oxacillin, or nafcillin for MSSA bloodstream infections.

Key Concept

Antibicrobial de-escalation for Methicillin-Susceptible Staphylococcus aureus (MSSA) bacteremia
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Topics

Infectious Diseases

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