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Question

Difficulty: MediumInfectious Diseases

A 62-year-old woman is evaluated on the third day of hospitalization for a central line-associated bloodstream infection. She has been receiving total parenteral nutrition through a central venous catheter for short bowel syndrome. Three days ago, she experienced the sudden onset of rigors, a temperature of 39.2°C (102.6°F), and a blood pressure of 90/60 mmHg. Blood cultures drawn from both the central catheter and a peripheral vein revealed Gram-positive cocci in clusters. The catheter was promptly removed, and empiric intravenous vancomycin and cefepime were started. Today, she feels well and is afebrile with normal hemodynamics. Final blood culture results confirm the presence of Staphylococcus aureus in all bottles. Susceptibility testing indicates the isolate is resistant to penicillin but susceptible to oxacillin, cefazolin, and vancomycin. Which of the following is the most appropriate modification to her antimicrobial therapy?

  1. Change therapy to intravenous cefazolinAnswer
  2. B
    Switch to intravenous vancomycin monotherapy
  3. C
    Switch to intravenous cefepime monotherapy
  4. D
    Make no changes to the current dual-drug regimen
  5. E
    Change therapy to oral trimethoprim-sulfamethoxazole

Answer

Change therapy to intravenous cefazolin
The correct answer is changing therapy to intravenous cefazolin. Once blood cultures finalize with methicillin-susceptible Staphylococcus aureus (MSSA), antimicrobial therapy must be appropriately de-escalated. Antistaphylococcal beta-lactams, such as cefazolin, nafcillin, or oxacillin, are the treatments of choice for MSSA bacteremia. They exhibit superior bactericidal activity compared to vancomycin and have been consistently associated with lower mortality and treatment failure rates in patients with MSSA bloodstream infections.

Step-by-Step Solution

1
Identify the infecting pathogen and its resistance profile.
The pathogen is methicillin-susceptible Staphylococcus aureus (MSSA), as indicated by susceptibility to oxacillin and cefazolin.
Accurate identification of the organism and susceptibility guides targeted antimicrobial therapy.
2
Evaluate the current empiric antibiotic regimen against the final culture results.
The patient is currently on vancomycin (covers MRSA) and cefepime (covers Pseudomonas and other Gram-negatives).
Empiric therapy is intentionally broad to cover potential life-threatening pathogens before culture results are available.
3
Apply principles of antimicrobial stewardship to de-escalate therapy.
The regimen should be narrowed to target MSSA specifically. Intravenous cefazolin (or nafcillin/oxacillin) is the drug of choice.
Antistaphylococcal beta-lactams are superior to vancomycin for MSSA infections, offering faster clearance of bacteremia and reduced mortality. Broad-spectrum agents like cefepime are unnecessary.

Key Concept

Patients with methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia should be treated with an intravenous antistaphylococcal beta-lactam (e.g., cefazolin, nafcillin, or oxacillin) rather than vancomycin due to superior clinical outcomes.
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Topics

Infectious Diseases

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