Examkin

Question

Difficulty: MediumInfectious Diseases

A 42-year-old man is admitted to the hospital with a 3-day history of high fever, severe chills, and profound fatigue. He has a history of intravenous drug use. His temperature on admission is 39.2°C (102.6°F), blood pressure is 112/68 mm Hg, and pulse is 108/min. Physical examination reveals needle track marks on both antecubital fossae and a new holosystolic murmur at the left lower sternal border that increases in intensity with inspiration. Multiple sets of blood cultures are drawn, and empiric intravenous vancomycin is initiated. A transthoracic echocardiogram confirms a 1.4-cm vegetation on the tricuspid valve. On hospital day 3, the patient is clinically stable, and his temperature has decreased to 37.6°C (99.7°F). Final blood culture reports indicate growth of *Staphylococcus aureus* in 4 out of 4 bottles. Susceptibility testing demonstrates the organism is resistant to penicillin but susceptible to oxacillin, cefazolin, and vancomycin. He has no known drug allergies.

Which of the following is the most appropriate next step in antibiotic management?

  1. Discontinue vancomycin and initiate intravenous cefazolinAnswer
  2. B
    Continue intravenous vancomycin as monotherapy
  3. C
    Add intravenous gentamicin to the current vancomycin regimen
  4. D
    Discontinue vancomycin and initiate intravenous linezolid
  5. E
    Discontinue vancomycin and initiate oral trimethoprim-sulfamethoxazole

Answer

Discontinue vancomycin and initiate intravenous cefazolin
The correct decision is to discontinue vancomycin and initiate intravenous cefazolin. The patient presents with right-sided infective endocarditis secondary to intravenous drug use. Blood cultures have confirmed Methicillin-Susceptible *Staphylococcus aureus* (MSSA), indicated by susceptibility to oxacillin. For severe MSSA infections, including bacteremia and endocarditis, intravenous antistaphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the standard of care. They are strongly preferred over vancomycin because they exhibit more rapid bactericidal activity, which translates into lower rates of clinical failure, relapse, and overall mortality. Proper antibiotic stewardship requires narrowing from broad empiric MRSA coverage to targeted beta-lactam therapy once MSSA is confirmed.

Step-by-Step Solution

1
Analyze the clinical presentation and diagnostic findings.
The patient has a tricuspid valve vegetation and a history of intravenous drug use, confirming a diagnosis of right-sided infective endocarditis.
Establishing the site and severity of the infection dictates the required duration and route of antimicrobial therapy.
2
Interpret the blood culture and susceptibility data.
The pathogen is identified as Staphylococcus aureus that is susceptible to oxacillin and cefazolin, making it Methicillin-Susceptible Staphylococcus aureus (MSSA).
Pathogen identification and susceptibility profiles are critical for transitioning from empiric broad-spectrum therapy to targeted therapy.
3
Select the optimal targeted pharmacotherapy.
The empiric vancomycin must be discontinued and replaced with a targeted intravenous antistaphylococcal beta-lactam, such as cefazolin or nafcillin.
Beta-lactams provide superior bactericidal activity, faster clearance of bacteremia, and significantly improved survival outcomes compared to vancomycin for MSSA infections.

Key Concept

For severe infections caused by Methicillin-Susceptible Staphylococcus aureus (MSSA), such as infective endocarditis, empiric vancomycin should be discontinued and therapy narrowed to an intravenous antistaphylococcal beta-lactam (e.g., cefazolin, nafcillin, or oxacillin) to improve clinical outcomes.
Rate this question

Topics

Infectious Diseases

More questions from this topic