A 71-year-old woman who resides in a skilled nursing facility is evaluated for the sudden … — USMLE Step 2 CK

A $71$ -year-old woman who resides in a skilled nursing facility is evaluated for the sudden onset of severe, foul-smelling, watery diarrhea. She reports having up to eight bowel movements per day for the last $48$ hours, accompanied by mild abdominal cramping. Three weeks prior, she completed a $10$ -day course of oral clindamycin for a tooth abscess. Her temperature is $38.2^\circ\text{C}$ ( $100.8^\circ\text{F}$ ), blood pressure is $112/70\text{ mmHg}$ , and pulse is $98/\text{min}$ . Abdominal examination reveals hyperactive bowel sounds and diffuse mild tenderness, but the abdomen is soft and non-distended. Laboratory testing shows a serum leukocyte count of $18,500/\text{mm}^3$ . Stool polymerase chain reaction testing is positive for *Clostridioides difficile* toxin genes. Which of the following is the most appropriate initial pharmacotherapy for this patient?

A
Intravenous ceftriaxone
B
Intravenous vancomycin
C
Oral metronidazole
Oral vancomycinAnswer
E
Oral ciprofloxacin

Answer

Oral vancomycin

The correct answer is oral vancomycin. It is recommended as a first-line therapy for an initial episode of *Clostridioides difficile* infection. When administered orally, vancomycin is poorly absorbed into the systemic circulation, which is a therapeutic advantage in this context because it allows the drug to achieve extremely high and effective bactericidal concentrations directly within the lumen of the colon where the infection resides.

Step-by-Step Solution

Identify the clinical syndrome and diagnosis.

The patient has acute watery diarrhea, leukocytosis, a history of recent clindamycin use, and a positive stool assay, confirming a diagnosis of Clostridioides difficile infection.

Recent antibiotic use alters gut flora, allowing C. difficile spores to proliferate and release toxins that cause mucosal inflammation and diarrhea.

Determine the appropriate guideline-directed treatment for an initial episode.

First-line therapy for an initial episode of C. difficile infection is either oral vancomycin or oral fidaxomicin.

Updated clinical guidelines prioritize these agents over metronidazole due to superior sustained cure rates and lower recurrence risks.

Select the correct route of administration.

Oral vancomycin is the correct choice, whereas intravenous vancomycin is incorrect.

Vancomycin must reach the colonic lumen to act on the infection. The intravenous formulation does not cross the colonic mucosa, making it ineffective for this indication.

Key Concept

Treatment of an initial episode of Clostridioides difficile infection requires intraluminal delivery of antibiotics; therefore, oral vancomycin or oral fidaxomicin is the first-line therapy.

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