A 72-year-old man with a history of chronic obstructive pulmonary disease and a mechanical… — USMLE Step 2 CK

A 72-year-old man with a history of chronic obstructive pulmonary disease and a mechanical mitral valve replacement is brought to the emergency department due to 5 days of fever, progressive dyspnea, and a cough producing frothy sputum. Temperature is 38.6°C (101.5°F), blood pressure is 105/60 mm Hg, pulse is 115/min, and respirations are 28/min. Oxygen saturation is 86% on room air. Lung auscultation reveals diffuse bilateral crackles. Cardiovascular examination reveals a new, loud holosystolic murmur at the apex radiating to the axilla. Chest radiograph shows cardiomegaly and bilateral perihilar alveolar opacities.

Laboratory studies on admission:
Leukocyte count: $18,500/\text{mm}^3$
Serum creatinine: $1.2\ \text{mg/dL}$
Thyroid-stimulating hormone (TSH): $0.15\ \mu\text{U/mL}$ (Normal: $0.4-4.0\ \mu\text{U/mL}$ )
Free T4: $0.8\ \text{ng/dL}$ (Normal: $0.9-2.4\ \text{ng/dL}$ )

The patient is intubated for acute respiratory failure. Blood cultures are drawn, and he is empirically started on intravenous vancomycin, cefepime, and furosemide. Transesophageal echocardiography demonstrates severe mitral regurgitation and a $12\text{-mm}$ mobile vegetation on the mechanical mitral valve.

On day 3, four out of four blood culture bottles grow *Enterococcus faecalis*. The isolate is susceptible to ampicillin, vancomycin, and high-level gentamicin. Repeat laboratory studies show a serum creatinine of $2.9\ \text{mg/dL}$ and a blood urea nitrogen of $52\ \text{mg/dL}$ .

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

Discontinue vancomycin and cefepime; initiate intravenous ampicillin and ceftriaxoneCevap
B
Discontinue vancomycin and cefepime; initiate intravenous ampicillin and gentamicin
C
Continue vancomycin; discontinue cefepime; initiate intravenous gentamicin
D
Maintain current antibiotics; administer intravenous methylprednisolone and albuterol
E
Maintain current antibiotics; initiate intravenous levothyroxine

Cevap

Discontinue vancomycin and cefepime; initiate intravenous ampicillin and ceftriaxone

This patient has *Enterococcus faecalis* prosthetic valve endocarditis complicated by acute valve failure (severe mitral regurgitation causing cardiogenic pulmonary edema) and acute kidney injury (AKI). *E. faecalis* requires synergistic bactericidal therapy for endocarditis eradication. Historically, ampicillin plus gentamicin was the sole standard of care. However, ampicillin combined with ceftriaxone is now recognized as equally efficacious for *E. faecalis* endocarditis and avoids aminoglycoside-induced nephrotoxicity. Ceftriaxone works synergistically by saturating penicillin-binding proteins (PBPs) 2 and 3, which allows ampicillin to more effectively bind its targets (PBPs 1, 4, and 5). Given the patient's acute rise in creatinine from

1.2

2.9\ \text{mg/dL}

(likely multifactorial from initial vancomycin use, poor perfusion, and sepsis), avoiding nephrotoxic agents like gentamicin is the most critical management step.

Adım Adım Çözüm

Analyze the clinical presentation and initial diagnostics

The patient has cardiogenic pulmonary edema due to acute severe mitral regurgitation caused by prosthetic valve endocarditis (PVE).

Fever, new holosystolic murmur, frothy sputum, and echocardiogram showing a vegetation confirm complicated PVE.

Evaluate the microbiological data

Blood cultures are positive for Enterococcus faecalis, which is susceptible to ampicillin, vancomycin, and high-level gentamicin.

Identifying the organism and sensitivities dictates the transition from empiric to definitive targeted therapy.

Assess the patient's current organ function

The serum creatinine has increased from 1.2 to 2.9 mg/dL, indicating acute kidney injury (AKI).

Renal function directly influences the choice of synergistic antibiotics for Enterococcal endocarditis.

Select the optimal definitive antibiotic regimen

Ampicillin plus ceftriaxone is selected.

Ampicillin plus ceftriaxone provides equivalent bactericidal synergy to ampicillin plus gentamicin but avoids aminoglycoside-induced nephrotoxicity, which is critical in a patient with active AKI.

Anahtar Kavram

Treatment of Enterococcus faecalis prosthetic valve endocarditis in the setting of acute kidney injury requires dual beta-lactam therapy (ampicillin and ceftriaxone) to achieve bactericidal synergy while avoiding aminoglycoside nephrotoxicity.

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