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Difficulty: HardPharmacologic Interventions

A 59-year-old man is admitted to the hospital with a 3-week history of severe fatigue, night sweats, and intermittent chills. His past medical history is significant for benign prostatic hyperplasia with recurrent urinary tract infections, as well as chronic kidney disease stage 4 secondary to hypertensive nephrosclerosis. His baseline estimated glomerular filtration rate is 22 mL/min/1.73 m². Current home medications include amlodipine, tamsulosin, and sodium bicarbonate. On examination, temperature is 38.3°C (100.9°F), blood pressure is 138/85 mm Hg, and pulse is 96/min. Cardiovascular examination reveals a new 3/6 holosystolic murmur loudest at the cardiac apex. Dermatologic examination shows several painful, violaceous nodules on the palmar aspects of the fingers. Transesophageal echocardiography demonstrates a 1.2-cm oscillating vegetation on the mitral valve. Blood cultures are drawn, and all four bottles grow *Enterococcus faecalis*. Antimicrobial susceptibility testing reveals the isolate is susceptible to ampicillin, vancomycin, and linezolid, with no high-level aminoglycoside resistance detected. Which of the following is the most appropriate definitive intravenous pharmacotherapy for this patient's infection?

  1. Ampicillin and ceftriaxoneAnswer
  2. B
    Ampicillin and gentamicin
  3. C
    Vancomycin and gentamicin
  4. D
    Linezolid
  5. E
    Ceftriaxone and azithromycin

Answer

The combination of ampicillin and ceftriaxone is the most appropriate therapy.
Enterococcus faecalis typically requires combination therapy to achieve the bactericidal activity necessary to cure infective endocarditis. Historically, this was achieved with a cell-wall active agent (like ampicillin) plus an aminoglycoside (like gentamicin). However, the combination of ampicillin and ceftriaxone has emerged as an equally efficacious, first-line standard of care. Ampicillin inhibits penicillin-binding proteins (PBPs) 4 and 5, while ceftriaxone inhibits PBPs 2 and 3. This dual-PBP blockade results in synergistic bactericidal activity. This regimen is particularly ideal for this patient with stage 4 chronic kidney disease, as it completely avoids the substantial nephrotoxicity associated with prolonged aminoglycoside courses.

Step-by-Step Solution

1
Identify the patient's diagnosis and underlying comorbidities.
The patient has native valve infective endocarditis caused by Enterococcus faecalis, complicated by underlying stage 4 chronic kidney disease.
Comorbidities, specifically renal impairment, dictate the safety profile required for prolonged intravenous antimicrobial therapy.
2
Determine the pharmacological requirements for treating Enterococcal endocarditis.
E. faecalis endocarditis requires synergistic combination therapy to achieve necessary bactericidal activity, as monotherapy with standard beta-lactams is only bacteriostatic.
Host immune defenses are limited within cardiac vegetations, necessitating bactericidal rather than bacteriostatic drug action.
3
Select the optimal regimen that balances bactericidal synergy with renal safety.
Ampicillin combined with ceftriaxone provides dual-mechanism synergy without the nephrotoxicity associated with the traditional ampicillin plus gentamicin regimen.
In a patient with an eGFR of 22 mL/min/1.73 m², avoiding aminoglycoside-induced acute kidney injury is a primary management goal.

Key Concept

Dual beta-lactam therapy (ampicillin plus ceftriaxone) provides necessary bactericidal synergy for Enterococcus faecalis endocarditis while averting aminoglycoside-induced nephrotoxicity in patients with underlying chronic kidney disease.
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Pharmacologic Interventions

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