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Difficulty: MediumInfectious Diseases

A 62-year-old man is hospitalized for severe, unremitting lower back pain and fever. His temperature is 38.8°C (101.8°F), blood pressure is 130/80 mm Hg, and pulse is 98/min. Physical examination reveals focal tenderness to palpation over the L4 and L5 spinous processes. Magnetic resonance imaging of the lumbar spine confirms L4-L5 vertebral osteomyelitis. Blood cultures are drawn, and the patient is empirically started on intravenous vancomycin and ceftriaxone. On day 3 of hospitalization, he is clinically stable and afebrile. Final blood culture results return positive for Staphylococcus aureus. Susceptibility testing shows resistance to penicillin, and susceptibility to oxacillin, cefazolin, vancomycin, and daptomycin. Which of the following is the most appropriate next step in antibiotic therapy?

  1. Discontinue the current regimen and begin intravenous cefazolinAnswer
  2. B
    Discontinue ceftriaxone and continue intravenous vancomycin
  3. C
    Continue the current regimen of vancomycin and ceftriaxone
  4. D
    Discontinue the current regimen and begin intravenous daptomycin
  5. E
    Continue the current regimen and add oral rifampin

Answer

Discontinue the current regimen and begin intravenous cefazolin.
The patient has methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia and native vertebral osteomyelitis. For severe MSSA infections, anti-staphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the definitive treatment of choice. They are superior to vancomycin in terms of bactericidal activity and overall clinical outcomes, including lower mortality rates and reduced risk of relapse. Transitioning from broad-spectrum empiric coverage to a targeted, narrow-spectrum beta-lactam is the most appropriate management step and aligns with core principles of antibiotic stewardship.

Step-by-Step Solution

1
Analyze the patient's presentation and diagnostic findings.
The patient has native vertebral osteomyelitis and bacteremia caused by Staphylococcus aureus.
Establishing the site and severity of infection dictates the required duration and route of therapy.
2
Review the antimicrobial susceptibility report.
The isolate is susceptible to oxacillin and cefazolin, confirming it is methicillin-susceptible Staphylococcus aureus (MSSA).
Susceptibility data is necessary to transition from broad-spectrum empiric therapy to definitive targeted therapy.
3
Select the optimal definitive antimicrobial agent.
Intravenous cefazolin (or an anti-staphylococcal penicillin like nafcillin/oxacillin) is selected over vancomycin.
Beta-lactam antibiotics provide superior bactericidal activity against MSSA compared to vancomycin, leading to lower mortality and relapse rates.

Key Concept

Definitive therapy for methicillin-susceptible Staphylococcus aureus (MSSA) severe infections (e.g., bacteremia, osteomyelitis) should utilize an anti-staphylococcal beta-lactam such as cefazolin or nafcillin, as these agents are clinically superior to vancomycin.
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Topics

Infectious Diseases

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