A 54-year-old man with a history of end-stage renal disease on hemodialysis is currently h… — USMLE Step 2 CK

A 54-year-old man with a history of end-stage renal disease on hemodialysis is currently hospitalized for management of suspected endocarditis. He presented three days ago with a two-week history of fatigue, severe night sweats, and intermittent fevers. His hemodialysis is accessed via a right internal jugular tunneled catheter. Vital signs today show a temperature of $39.4^\circ\text{C}$ ( $102.9^\circ\text{F}$ ), blood pressure of $108/64\text{ mm Hg}$ , pulse of $115/\text{min}$ , and respiratory rate of $16/\text{min}$ . Cardiac auscultation reveals a new high-pitched, blowing early diastolic murmur heard best at the left sternal border. Transesophageal echocardiography reveals a $1.5\text{-cm}$ oscillating vegetation on the aortic valve with severe aortic regurgitation. At the time of admission, empiric intravenous vancomycin and cefepime were initiated. Blood cultures drawn before the first antibiotic dose are now growing *Staphylococcus aureus*. The isolate is sensitive to oxacillin, cefazolin, and vancomycin, but resistant to penicillin. Which of the following is the most appropriate next step in the pharmacologic management of this patient?

Discontinue vancomycin and cefepime, and begin intravenous cefazolinAnswer
B
Continue intravenous vancomycin and discontinue cefepime
C
Discontinue vancomycin and cefepime, and begin oral clindamycin
D
Continue the current regimen and add intravenous gentamicin
E
Discontinue vancomycin and cefepime, and begin intravenous daptomycin

Answer

Discontinue vancomycin and cefepime, and begin intravenous cefazolin

For methicillin-susceptible Staphylococcus aureus (MSSA) infective endocarditis, anti-staphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the treatment of choice. They have been shown to be more rapidly bactericidal and are associated with significantly lower rates of treatment failure and mortality compared to vancomycin. Therefore, the empiric regimen should be de-escalated to a targeted, narrow-spectrum beta-lactam agent once susceptibility results confirm the presence of MSSA.

Step-by-Step Solution

Identify the primary diagnosis based on clinical and diagnostic findings.

The patient has native valve infective endocarditis, complicated by severe aortic regurgitation.

Establishes the severity of the infection and dictates the need for aggressive, bactericidal intravenous therapy.

Analyze the microbiological culture and susceptibility data.

Blood cultures are growing methicillin-susceptible Staphylococcus aureus (MSSA).

Guides the transition from empiric therapy to targeted antimicrobial therapy.

Select the optimal pharmacotherapy for the identified pathogen.

Intravenous cefazolin (or another anti-staphylococcal beta-lactam like nafcillin) is selected.

Anti-staphylococcal beta-lactams are superior to vancomycin for MSSA infections, providing better clinical outcomes and faster bacterial clearance.

Key Concept

For methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia and infective endocarditis, anti-staphylococcal beta-lactams (e.g., cefazolin, nafcillin) are the treatment of choice and are superior to vancomycin.

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