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Difficulty: MediumInfectious Diseases

A 62-year-old man is evaluated in the hospital on hospital day 3. He was initially admitted for fever, chills, and a warm, swollen right calf. On admission, his temperature was 39.1 C (102.4 F), blood pressure was 105/65 mm Hg, and pulse was 110/min. He was started on empiric intravenous vancomycin and piperacillin-tazobactam. Today, his temperature is 37.4 C (99.3 F), blood pressure is 120/75 mm Hg, and pulse is 82/min. The erythema on his right calf has significantly decreased. Blood cultures drawn on admission are positive for Staphylococcus aureus in 2 of 2 bottles. Susceptibility testing shows the isolate is resistant to penicillin but susceptible to oxacillin, cefazolin, and vancomycin. The patient has no history of medication allergies. Which of the following is the most appropriate next step in management?

  1. Switch to intravenous cefazolinAnswer
  2. B
    Discontinue piperacillin-tazobactam and continue intravenous vancomycin
  3. C
    Discontinue vancomycin and continue intravenous piperacillin-tazobactam
  4. D
    Switch to intravenous daptomycin
  5. E
    Continue the current antibiotic regimen

Answer

Switch to intravenous cefazolin
The patient has methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia. For MSSA bacteremia, targeted beta-lactams such as first-generation cephalosporins (e.g., cefazolin) or anti-staphylococcal penicillins (e.g., nafcillin, oxacillin) are the treatments of choice. They have been consistently shown to be superior to vancomycin for MSSA infections, resulting in faster bacterial clearance, lower rates of clinical failure, and reduced mortality. Because the isolate is susceptible and the patient has no beta-lactam allergies, de-escalating to cefazolin is the most appropriate next step.

Step-by-Step Solution

1
Analyze the blood culture and susceptibility results.
The pathogen is identified as methicillin-susceptible Staphylococcus aureus (MSSA) because it is susceptible to oxacillin and cefazolin.
Identifying the specific susceptibility pattern is required to transition from empiric to targeted, definitive therapy.
2
Evaluate the patient's current empiric antibiotic regimen against the culture data.
The current regimen of vancomycin and piperacillin-tazobactam is overly broad and suboptimal for MSSA.
Vancomycin covers MRSA but is inferior to beta-lactams for MSSA. Piperacillin-tazobactam covers Pseudomonas and anaerobes, which are not present in this patient's cultures.
3
Select the most appropriate definitive therapy based on antimicrobial stewardship principles.
Intravenous cefazolin should be initiated.
Cefazolin (or an anti-staphylococcal penicillin like nafcillin) provides targeted, narrow-spectrum coverage and has proven superiority over vancomycin for MSSA bacteremia.

Key Concept

Methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia should be treated with a narrow-spectrum 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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