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Difficulty: MediumCardiovascular System

A 28-year-old man presents to the emergency department with a 4-day history of high fevers, chills, and sharp, pleuritic chest pain. He also reports a cough productive of scant, blood-tinged sputum. His temperature is 39.1∘C39.1^\circ\text{C} (102.4∘F102.4^\circ\text{F}), blood pressure is 112/68 mmHg112/68\text{ mmHg}, pulse is 118/min118/\text{min}, and respiratory rate is 22/min22/\text{min}. Oxygen saturation is 94%94\% on room air. Physical examination reveals prominent needle track marks on his forearms. Cardiac auscultation demonstrates a grade 3/63/6 holosystolic murmur at the left lower sternal border; the murmur's intensity increases significantly during inspiration. Pulmonary auscultation reveals scattered crackles in both lung fields. A chest radiograph demonstrates multiple bilateral peripheral nodular opacities, several of which have central cavitation. Three sets of blood cultures are obtained. Which of the following is the most appropriate initial pharmacotherapy for this patient?

  1. Intravenous vancomycinAnswer
  2. B
    Intravenous ceftriaxone and azithromycin
  3. C
    Oral isoniazid, rifampin, pyrazinamide, and ethambutol
  4. D
    Intravenous heparin infusion
  5. E
    Intravenous ampicillin-sulbactam

Answer

Intravenous vancomycin
The patient's presentation of high fever, intravenous drug use, a tricuspid regurgitation murmur (holosystolic at the left lower sternal border, augmenting with inspiration), and cavitary pulmonary lesions is highly characteristic of right-sided infective endocarditis complicated by septic pulmonary emboli. Staphylococcus aureus, including methicillin-resistant strains (MRSA), is the most common etiologic agent in this population. Empiric therapy with an agent that provides robust MRSA coverage, such as intravenous vancomycin, is necessary immediately after obtaining blood cultures.

Step-by-Step Solution

1
Analyze the patient's demographic risk factors and presenting vital signs.
The patient is a young intravenous drug user presenting with acute fever, tachycardia, and hypoxemia.
Identifying risk factors helps prioritize infectious etiologies such as endovascular infections.
2
Evaluate the physical examination findings, specifically the cardiac auscultation.
A holosystolic murmur at the left lower sternal border that augments with inspiration indicates tricuspid regurgitation.
Right-sided murmurs classically increase with inspiration (Carvallo sign) due to increased venous return to the right heart.
3
Interpret the radiographic findings in the context of the clinical picture.
Multiple cavitating peripheral nodular opacities in the lungs represent septic pulmonary emboli.
Vegetations on the tricuspid valve can dislodge and travel to the pulmonary vasculature, causing localized infarction and abscess formation.
4
Synthesize a diagnosis and determine the optimal empiric antibiotic regimen.
The diagnosis is right-sided infective endocarditis. Empiric therapy must cover Staphylococcus aureus (including MRSA).
Staphylococcus aureus is responsible for the vast majority of right-sided endocarditis cases in intravenous drug users, requiring broad-spectrum Gram-positive coverage with intravenous vancomycin until cultures result.

Key Concept

Right-sided infective endocarditis in intravenous drug users commonly presents with tricuspid regurgitation and septic pulmonary emboli, requiring empiric coverage for MRSA with intravenous vancomycin.
Estimated Time:1m 30s
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Topics

Cardiovascular System

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