A 32-year-old man comes to the emergency department because of a 5-day history of high fev… — USMLE Step 2 CK

A $32$ -year-old man comes to the emergency department because of a $5$ -day history of high fever, profound fatigue, and severe joint pains. His past medical history is significant for severe opioid use disorder, and he reports injecting heroin daily. His temperature is $39.4^{\circ}\text{C}$ ( $102.9^{\circ}\text{F}$ ), blood pressure is $114/68 \text{ mm Hg}$ , pulse is $118/\text{min}$ , and respiratory rate is $18/\text{min}$ . Physical examination shows multiple needle track marks in both antecubital fossae. Cardiovascular auscultation reveals a regular tachycardia and a grade $3/6$ holosystolic murmur at the left lower sternal border; the murmur's intensity increases with inspiration. The lungs are clear to auscultation bilaterally. Small, linear, dark-red hemorrhages are noted beneath the nail beds of his right hand. Three sets of blood cultures are obtained. Which of the following is the most appropriate next step in management?

Administration of intravenous vancomycinAnswer
B
Postponement of antimicrobial therapy until culture susceptibilities are finalized
C
Administration of intravenous cefazolin
D
Administration of intravenous furosemide
E
Echocardiography prior to initiating antimicrobial therapy

Answer

The correct answer is the administration of intravenous vancomycin.

The correct answer is the administration of intravenous vancomycin. The patient's presentation of high fever, fatigue, and joint pain in the setting of severe opioid use disorder is highly suspicious for acute infective endocarditis. The physical examination confirms right-sided involvement, characterized by a holosystolic murmur at the left lower sternal border that increases with inspiration (Carvallo's sign, indicating tricuspid regurgitation). Splinter hemorrhages further support this endovascular diagnosis. In patients who inject drugs, Staphylococcus aureus (especially methicillin-resistant S. aureus, or MRSA) is the most common causative organism. Because acute endocarditis can rapidly result in hemodynamic instability and septic pulmonary emboli, empiric antibiotic therapy must be initiated immediately after obtaining blood cultures. Intravenous vancomycin is the preferred empiric agent due to its reliable coverage against MRSA.

Step-by-Step Solution

Identify the primary diagnosis based on the clinical presentation.

The combination of fever, intravenous drug use, splinter hemorrhages, and an inspiratory-augmented holosystolic murmur indicates acute right-sided (tricuspid) infective endocarditis.

Intravenous drug use is a major risk factor for right-sided endocarditis, which frequently presents with a tricuspid regurgitation murmur (increases with inspiration due to increased venous return).

Determine the appropriate timing for pharmacotherapy.

Empiric antimicrobial therapy must be initiated immediately after drawing blood cultures.

Acute endocarditis is a rapidly progressive, fulminant condition; delaying treatment for culture results or imaging greatly increases the risk of morbidity and mortality.

Select the optimal empiric antibiotic regimen.

Intravenous vancomycin is the initial drug of choice.

Vancomycin provides essential coverage against methicillin-resistant Staphylococcus aureus (MRSA), which is highly prevalent in endocarditis associated with intravenous drug use.

Key Concept

Empiric antibiotic therapy for right-sided infective endocarditis in intravenous drug users must be initiated immediately after obtaining blood cultures and should include intravenous vancomycin to cover methicillin-resistant Staphylococcus aureus (MRSA).

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