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Difficulty: HardInfectious Diseases

A 29-year-old man is evaluated in the hospital for ongoing fever. He was admitted 4 days ago with high fevers, chills, and pleuritic chest pain. His medical history is significant for opioid use disorder with active intravenous heroin use. On admission, his temperature was 39.2°C (102.6°F). Physical examination revealed a new holosystolic murmur at the lower left sternal border. Computed tomography of the chest showed multiple peripheral cavitary lesions. Two sets of blood cultures were drawn, and he was started on empiric intravenous vancomycin and ceftriaxone. A transthoracic echocardiogram demonstrated a 1.5-cm mobile vegetation on the anterior leaflet of the tricuspid valve. Today, the patient's temperature is 38.4°C (101.1°F). The admission blood cultures are now growing methicillin-susceptible *Staphylococcus aureus* (MSSA). Which of the following is the most appropriate next step in pharmacotherapy?

  1. Discontinue current antibiotics and start intravenous cefazolinAnswer
  2. B
    Continue intravenous vancomycin and discontinue intravenous ceftriaxone
  3. C
    Continue intravenous vancomycin, discontinue intravenous ceftriaxone, and add intravenous gentamicin
  4. D
    Discontinue current antibiotics and start oral linezolid
  5. E
    Discontinue current antibiotics and start intravenous daptomycin

Answer

Discontinue current antibiotics and start intravenous cefazolin
The correct answer requires recognizing that for severe, invasive infections caused by methicillin-susceptible Staphylococcus aureus (MSSA), antistaphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the superior treatment choice. Although vancomycin is an appropriate initial empiric choice to cover potential MRSA, it has slower bactericidal activity against MSSA compared to beta-lactams. Continuing vancomycin once MSSA is confirmed is associated with prolonged bacteremia, higher rates of treatment failure, and increased mortality. Therefore, the most appropriate next step in antibiotic stewardship and patient management is to discontinue both the vancomycin and the ceftriaxone (which was covering gram-negatives) and initiate targeted therapy with intravenous cefazolin.

Step-by-Step Solution

1
Identify the primary diagnosis based on the clinical presentation
The patient has native valve right-sided infective endocarditis complicated by septic pulmonary emboli.
The combination of intravenous drug use, a new tricuspid regurgitation murmur, cavitary lung lesions, a large tricuspid vegetation, and positive blood cultures confirms the diagnosis.
2
Evaluate the current empiric antibiotic regimen against the culture results
The patient is receiving empiric vancomycin and ceftriaxone, but the pathogen is identified as methicillin-susceptible Staphylococcus aureus (MSSA).
Broad-spectrum empiric therapy must be narrowed and optimized once the exact pathogen and its susceptibilities are identified.
3
Determine the optimal targeted pharmacotherapy for the identified pathogen
Therapy should be de-escalated to an intravenous antistaphylococcal beta-lactam, such as cefazolin, nafcillin, or oxacillin.
Beta-lactams provide superior bactericidal activity, faster clearance of bacteremia, and significantly improved survival rates compared to vancomycin for MSSA endovascular infections.

Key Concept

De-escalation of empiric therapy to an antistaphylococcal beta-lactam (e.g., cefazolin, nafcillin) is the standard of care for methicillin-susceptible Staphylococcus aureus (MSSA) endocarditis, as beta-lactams are clinically superior to vancomycin for MSSA.
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Infectious Diseases

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