A 68-year-old woman is evaluated in the hospital for new-onset diarrhea. She was admitted … — USMLE Step 2 CK

A 68-year-old woman is evaluated in the hospital for new-onset diarrhea. She was admitted seven days ago for the management of community-acquired pneumonia and has been receiving intravenous ceftriaxone and azithromycin. Over the past two days, she has developed frequent, profuse, watery bowel movements accompanied by diffuse abdominal cramping. Her temperature is $38.2^{\circ}\mathrm{C}$ ( $100.8^{\circ}\mathrm{F}$ ), blood pressure is $112/74\;\mathrm{mmHg}$ , and pulse is $98/\mathrm{min}$ . Physical examination reveals mild lower abdominal tenderness without guarding or rebound. Laboratory studies show a leukocyte count of $15,500/\mathrm{mm}^3$ . A stool enzyme immunoassay is positive for *Clostridioides difficile* glutamate dehydrogenase antigen and toxin A/B. Which of the following is the most appropriate targeted pharmacotherapy for this patient's gastrointestinal infection?

Oral vancomycinAnswer
B
Intravenous vancomycin
C
Oral metronidazole
D
Intravenous piperacillin-tazobactam
E
Oral ciprofloxacin

Answer

Oral vancomycin

The patient has *Clostridioides difficile* infection (CDI) as evidenced by new-onset watery diarrhea, leukocytosis, and a positive stool toxin assay following recent broad-spectrum antibiotic use. The first-line targeted treatment for an initial episode of non-fulminant CDI is oral vancomycin (or oral fidaxomicin). Oral administration ensures that high concentrations of the drug reach the colonic lumen, where the infection is localized, while minimizing systemic absorption.

Step-by-Step Solution

Identify the primary diagnosis based on the clinical presentation and laboratory findings.

The patient has a confirmed Clostridioides difficile infection (CDI), characterized by recent antibiotic use, watery diarrhea, leukocytosis, and a positive stool toxin assay.

Establishing the correct diagnosis is required to select the appropriate targeted antimicrobial therapy.

Determine the optimal first-line treatment for an initial episode of non-fulminant CDI.

Current guidelines recommend oral vancomycin or oral fidaxomicin as the first-line targeted therapies.

These agents achieve high therapeutic concentrations directly at the site of infection in the colonic lumen without significant systemic absorption.

Key Concept

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

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