A 72-year-old man is evaluated in a skilled nursing facility due to a 4-day history of fre… — USMLE Step 2 CK

A $72$ -year-old man is evaluated in a skilled nursing facility due to a $4$ -day history of frequent, watery, foul-smelling stools and diffuse lower abdominal cramping. Two weeks ago, he completed a $7$ -day course of oral amoxicillin-clavulanate for a chronic obstructive pulmonary disease exacerbation. His temperature is $37.8^{\circ}\text{C}$ ( $100.0^{\circ}\text{F}$ ), blood pressure is $128/78\text{ mm Hg}$ , and pulse is $92/\text{min}$ . Physical examination reveals mild, diffuse abdominal tenderness without guarding or rebound. Laboratory testing shows a leukocyte count of $14,000/\text{mm}^3$ and a serum creatinine of $1.1\text{ mg/dL}$ . A stool enzyme immunoassay is positive for both glutamate dehydrogenase antigen and *Clostridioides difficile* toxins A and B. Which of the following is the most appropriate targeted pharmacotherapy for this patient's current condition?

Oral fidaxomicinAnswer
B
Intravenous vancomycin
C
Oral metronidazole
D
Intravenous metronidazole
E
Fecal microbiota transplantation

Answer

Oral fidaxomicin

The patient has an initial episode of non-severe *Clostridioides difficile* infection (CDI), characterized by characteristic diarrhea following recent antibiotic exposure, a leukocyte count

< 15,000/\text{mm}^3

, and a serum creatinine

< 1.5\text{ mg/dL}

. According to current guidelines, the preferred first-line treatment for an initial episode of CDI is oral fidaxomicin. Oral vancomycin is an acceptable alternative. Fidaxomicin is specifically favored because of its narrow spectrum of activity (preserving normal gut flora) and its association with significantly lower rates of CDI recurrence.

Step-by-Step Solution

Analyze the clinical presentation and recent history.

The patient has new-onset watery diarrhea and abdominal cramping following a recent course of amoxicillin-clavulanate.

Identifying the clinical syndrome and risk factors points toward antibiotic-associated diarrhea.

Interpret the diagnostic test results.

Stool immunoassay is positive for GDH antigen and C. difficile toxins A and B, confirming the diagnosis.

Positive GDH confirms the presence of the organism, while positive toxins confirm the toxigenic strain causing active infection.

Assess disease severity.

The patient has a leukocyte count of 14,000/mm^3 (which is less than 15,000/mm^3) and a normal serum creatinine, with no signs of shock or megacolon.

Severity classification determines the appropriate route and choice of antimicrobial therapy.

Select the guideline-recommended first-line therapy.

Oral fidaxomicin or oral vancomycin is indicated for an initial episode of non-severe C. difficile infection.

Current IDSA/SHEA guidelines prioritize oral fidaxomicin due to its narrow spectrum and lower recurrence rates.

Key Concept

The first-line pharmacotherapy for an initial episode of non-fulminant Clostridioides difficile infection is oral fidaxomicin or oral vancomycin.

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