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Difficulty: MediumGastroenterology and Hepatology

A 6868-year-old man is evaluated on postoperative day 55 following a partial colectomy for recurrent uncomplicated diverticulitis. Over the past 2424 hours, he has developed a fever, tachycardia, and new-onset copious, watery diarrhea. He reports mild, diffuse abdominal cramping but no nausea or vomiting. His current medications include intravenous fluids, prophylactic subcutaneous enoxaparin, and patient-controlled analgesia. He received a standard course of perioperative intravenous cefoxitin. His temperature is 38.6∘C38.6^\circ\text{C} (101.5∘F101.5^\circ\text{F}), blood pressure is 118/74 mm Hg118/74 \text{ mm Hg}, and pulse is 112/min112/\text{min}. On physical examination, the abdomen is mildly distended and diffusely tender to deep palpation, without rigidity or rebound tenderness. The surgical incision is clean, dry, and intact.

Laboratory studies show:
Leukocyte count: 18,500/mm318,500/\text{mm}^3

Arterial blood gas (room air):
pH: 7.327.32
pCO 2_2: 30 mm Hg30 \text{ mm Hg}
HCO 3−_3^-: 15 mEq/L15 \text{ mEq/L}

A stool enzyme immunoassay (EIA) is positive for *Clostridioides difficile* toxins A and B.

Which of the following is the most appropriate next step in management?

  1. Initiate oral vancomycinAnswer
  2. B
    Initiate intravenous vancomycin
  3. C
    Initiate intravenous piperacillin-tazobactam
  4. D
    Administer intravenous sodium bicarbonate
  5. E
    Obtain a portable chest radiograph

Answer

Initiate oral vancomycin therapy to treat the Clostridioides difficile infection directly within the gut lumen.
This patient has developed a hospital-acquired *Clostridioides difficile* infection (CDI), supported by the classic presentation of fever, leukocytosis, and copious watery diarrhea following recent antibiotic exposure. The correct management for a first episode of non-fulminant CDI is a 1010-day course of oral vancomycin or oral fidaxomicin. Because *C. difficile* causes disease strictly within the colonic lumen, the chosen antibiotic must achieve high intraluminal concentrations. Oral vancomycin is not absorbed systemically, allowing it to act locally on the colonic mucosa to eradicate the pathogen.

Step-by-Step Solution

1
Analyze the patient's clinical presentation and timeline.
The patient has fever, leukocytosis, and watery diarrhea on postoperative day 5 after receiving perioperative antibiotics.
Establishing the postoperative timeline helps rule out early causes of fever (like atelectasis) and points toward infection, particularly antibiotic-associated diarrhea.
2
Interpret the diagnostic test results.
The stool EIA is positive for C. difficile toxins A and B, confirming the diagnosis of Clostridioides difficile infection (CDI).
A positive toxin assay in the setting of compatible clinical symptoms establishes the indication for targeted pharmacotherapy.
3
Evaluate the arterial blood gas (ABG) values.
The patient has a metabolic acidosis (pH 7.32, HCO3- 15). Using Winter's formula, Expected pCO2 = (1.5 × 15) + 8 = 30.5 ± 2. The measured pCO2 is 30, indicating appropriate respiratory compensation.
Ruling out a superimposed primary respiratory disorder or uncompensated state ensures that systemic metabolic interventions (like sodium bicarbonate) are withheld appropriately.
4
Determine the optimal pharmacologic management.
Oral vancomycin or oral fidaxomicin is the preferred first-line therapy.
The medication must reach the colonic lumen; intravenous vancomycin is not secreted into the bowel and is ineffective for CDI.

Key Concept

The first-line treatment for an initial, non-fulminant episode of Clostridioides difficile infection is oral vancomycin or oral fidaxomicin; intravenous vancomycin is ineffective because it does not cross the gut mucosa.
Estimated Time:1m 15s
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Topics

Gastroenterology and Hepatology

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