A 65-year-old hospitalized patient develops profuse watery diarrhea (8 unformed stools per day), crampy abdominal pain, and leukocytosis (WBC 16,000/uL) five days after completing a course of clindamycin. Stool PCR is positive for Clostridioides difficile toxin. What is the first-line oral antibiotic of choice for this initial episode of C. difficile infection?

Answer and explanation

Correct answer: B. Oral Vancomycin 125 mg four times daily for 10 days

  1. Step 1: IDSA and SHEA guidelines establish oral Vancomycin (125 mg QID for 10 days) or oral Fidaxomicin (200 mg BID for 10 days) as the first-line therapies of choice for an initial episode of C. difficile colitis.
  2. Step 2: Oral metronidazole is no longer recommended as first-line due to inferior cure rates and higher recurrence rates.
  3. Step 3: Intravenous vancomycin is NOT excreted into the colonic lumen and is completely ineffective for C. difficile colitis.
Answer
Oral Vancomycin 125 mg four times daily for 10 days.
Why not the others: 'Oral Metronidazole' has inferior clinical cure rates and is relegated to third-line only when vancomycin/fidaxomicin are unavailable; 'Intravenous Ciprofloxacin' is a fluoroquinolone that promotes C. difficile; 'Intravenous Vancomycin' does not enter the gut lumen and is useless.

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