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Difficulty: HardCardiovascular System

A 32-year-old man with a history of intravenous drug use is admitted to the intensive care unit with a 4-day history of high fever, chills, and pleuritic chest pain. On physical examination, his temperature is 39.2°C (102.6°F), blood pressure is 110/65 mmHg, pulse is 112/min, and respirations are 22/min. Cardiovascular examination reveals a 3/6 holosystolic murmur best heard at the left lower sternal border that increases in intensity with inspiration. The lungs are clear to auscultation bilaterally. Empiric therapy with intravenous vancomycin and cefepime is initiated after blood cultures are drawn.

On hospital day 3, the patient develops acute respiratory distress. His oxygen saturation drops to 86% on room air. A chest radiograph reveals multiple bilateral nodular opacities with central cavitation. Echocardiography shows a 1.5-cm, highly mobile vegetation on the tricuspid valve with moderate tricuspid regurgitation. The left ventricular ejection fraction is 60%. All four blood culture bottles return positive for methicillin-susceptible Staphylococcus aureus (MSSA).

Which of the following is the most appropriate next step in the pharmacologic management of this patient?

  1. Switch to intravenous nafcillinAnswer
  2. B
    Continue intravenous vancomycin and cefepime
  3. C
    Add intravenous gentamicin to the current regimen
  4. D
    Administer intravenous furosemide and inhaled albuterol
  5. E
    Switch to oral linezolid

Answer

Switch to intravenous nafcillin
This patient has right-sided infective endocarditis (IE) complicated by septic pulmonary emboli. His history of intravenous drug use, new tricuspid regurgitation murmur (holosystolic, increasing in intensity with inspiration), and a large tricuspid vegetation confirm the diagnosis. The acute respiratory distress and cavitating nodular opacities on the chest radiograph are classic for septic emboli originating from the right heart and lodging in the pulmonary circulation. The blood cultures definitively identified methicillin-susceptible Staphylococcus aureus (MSSA). In the management of MSSA bacteremia and endocarditis, beta-lactam antibiotics (specifically anti-staphylococcal penicillins such as nafcillin or oxacillin, or first-generation cephalosporins like cefazolin) are the drugs of choice. They are highly bactericidal and have been consistently shown to be superior to vancomycin for clearing MSSA, resulting in lower rates of treatment failure and mortality. Therefore, principles of antimicrobial stewardship dictate that the empiric broad-spectrum regimen (vancomycin and cefepime) should be promptly discontinued and replaced with targeted intravenous nafcillin.

Step-by-Step Solution

1
Diagnose the primary condition based on the patient's risk factors and clinical presentation.
Right-sided infective endocarditis.
The patient has a history of intravenous drug use, high fever, a new tricuspid regurgitation murmur (holosystolic, left lower sternal border, louder with inspiration), and a large tricuspid vegetation.
2
Identify the cause of the sudden respiratory decline on hospital day 3.
Septic pulmonary emboli.
Right-sided cardiac vegetations frequently break off and embolize to the pulmonary circulation, causing hypoxia and classic chest radiograph findings of multiple cavitating nodular opacities.
3
Select the optimal targeted antimicrobial therapy based on culture results.
Intravenous nafcillin.
Blood cultures definitively isolated methicillin-susceptible Staphylococcus aureus (MSSA). For MSSA bacteremia, beta-lactam antibiotics like nafcillin or cefazolin are superior to vancomycin.

Key Concept

The optimal definitive treatment for methicillin-susceptible Staphylococcus aureus (MSSA) native valve infective endocarditis is a prolonged course of an intravenous anti-staphylococcal penicillin (e.g., nafcillin) or a first-generation cephalosporin (e.g., cefazolin), which provide superior clinical outcomes compared to vancomycin.
Estimated Time:1m 30s
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Topics

Cardiovascular System

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