A 68-year-old man comes to the clinic reporting the onset of frequent, watery, non-bloody … — USMLE Step 2 CK

A 68-year-old man comes to the clinic reporting the onset of frequent, watery, non-bloody diarrhea occurring up to $7$ times daily over the past $3$ days. He also notes mild, diffuse lower abdominal cramping. His medical history is significant for hypertension and hyperlipidemia. Two weeks ago, he completed a 10-day course of oral amoxicillin-clavulanate for acute bacterial sinusitis. His temperature is $38.1^\circ\text{C}$ ( $100.6^\circ\text{F}$ ), blood pressure is $118/76 \text{ mmHg}$ , and heart rate is $92/\text{min}$ . Physical examination reveals mild diffuse abdominal tenderness with normal bowel sounds; there is no guarding or rebound tenderness. Laboratory testing shows a leukocyte count of $14,500/\text{mm}^3$ and a serum creatinine of $1.1 \text{ mg/dL}$ (baseline $1.0 \text{ mg/dL}$ ). A stool nucleic acid amplification test is positive for *Clostridioides difficile* toxin genes. Which of the following is the most appropriate next step in management?

Administer oral fidaxomicinAnswer
B
Administer oral metronidazole
C
Administer intravenous vancomycin
D
Administer intravenous metronidazole
E
Refer for fecal microbiota transplantation

Answer

The correct approach is to administer oral fidaxomicin.

The most appropriate next step in management is the administration of oral fidaxomicin. This patient is presenting with an initial episode of *Clostridioides difficile* infection (CDI), likely precipitated by his recent course of amoxicillin-clavulanate. According to updated guidelines from the Infectious Diseases Society of America (IDSA) and Society for Healthcare Epidemiology of America (SHEA), oral fidaxomicin is the preferred first-line therapy for both non-severe and severe initial episodes of CDI. Oral vancomycin is an acceptable alternative. Fidaxomicin is preferred over vancomycin because it has a narrower spectrum of activity (preserving normal gut flora) and has been shown to result in lower rates of CDI recurrence.

Step-by-Step Solution

Identify the primary diagnosis based on the clinical presentation.

The patient has an initial episode of Clostridioides difficile infection (CDI).

The diagnosis is supported by the history of recent antibiotic use, acute watery diarrhea, and a positive stool nucleic acid amplification test for C. difficile toxins.

Assess the severity of the CDI episode.

This is a non-severe episode.

The patient is hemodynamically stable without signs of fulminant disease. Furthermore, the leukocyte count is less than

15,000/\text{mm}^3

and serum creatinine is less than

1.5 \text{ mg/dL}

Determine the most appropriate pharmacotherapy based on current guidelines.

Select oral fidaxomicin (or oral vancomycin).

Current Infectious Diseases Society of America (IDSA) guidelines recommend oral fidaxomicin as the preferred first-line agent for initial CDI (both non-severe and severe) to maximize clinical cure and reduce the risk of recurrence.

Key Concept

First-line pharmacotherapy for an initial episode of Clostridioides difficile infection.

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