A 71-year-old man is evaluated in the intensive care unit for new-onset abdominal distensi… — USMLE Step 2 CK

A 71-year-old man is evaluated in the intensive care unit for new-onset abdominal distension and altered mental status. He was admitted one week ago for treatment of healthcare-associated pneumonia and has been receiving intravenous piperacillin-tazobactam. Two days ago, he developed multiple episodes of watery diarrhea, but he has had no bowel movements for the past $18 \text{ hours}$ . Current temperature is $38.8^\circ\text{C}$ ( $101.8^\circ\text{F}$ ), blood pressure is $86/54 \text{ mmHg}$ , pulse is $122/\text{min}$ , and respirations are $24/\text{min}$ . Physical examination reveals a lethargic patient. The abdomen is grossly distended, tympanic to percussion, and diffusely tender with absent bowel sounds.

Laboratory results are as follows:

Parameter	Result	Reference Range
Leukocyte count	$32,000/\text{mm}^3$	$4,500-11,000/\text{mm}^3$
Serum creatinine	$2.4 \text{ mg/dL}$	$0.6-1.2 \text{ mg/dL}$
Lactic acid	$4.2 \text{ mmol/L}$	$0.5-1.0 \text{ mmol/L}$

An abdominal plain film shows a transverse colon diameter of $8.5 \text{ cm}$ without free intraperitoneal air. 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 pharmacologic intervention?

A
Intravenous vancomycin and intravenous metronidazole
B
Enteral fidaxomicin monotherapy
C
Enteral vancomycin and intravenous metronidazole
Enteral vancomycin, rectal vancomycin, and intravenous metronidazoleAnswer
E
Intravenous ceftriaxone and oral metronidazole

Answer

The most appropriate regimen for fulminant Clostridioides difficile infection complicated by an ileus is the combination of enteral vancomycin, rectal vancomycin, and intravenous metronidazole.

This patient presents with fulminant *Clostridioides difficile* infection (CDI) complicated by toxic megacolon and an ileus. Fulminant CDI is defined by the presence of hypotension or shock, ileus, or toxic megacolon. The standard of care for fulminant CDI is high-dose enteral vancomycin combined with intravenous metronidazole. Because this patient has an ileus (indicated by absent bowel sounds and a sudden cessation of diarrhea), enterally administered vancomycin is unlikely to reach the distal colon. Therefore, the addition of rectal vancomycin (via enemas) is required to ensure adequate drug delivery directly to the affected colonic mucosa.

Step-by-Step Solution

Analyze the patient's clinical presentation and laboratory values to categorize disease severity.

The patient has hypotension (

86/54 \text{ mmHg}

), a severely elevated leukocyte count (

32,000/\text{mm}^3

), and radiographic evidence of toxic megacolon (

8.5 \text{ cm}

diameter), confirming fulminant Clostridioides difficile infection.

Treatment regimens for Clostridioides difficile infection are strictly dictated by disease severity (non-severe, severe, or fulminant).

Identify specific gastrointestinal complications that alter drug pharmacokinetics.

The patient has an ileus, evidenced by absent bowel sounds and a lack of bowel movements for 18 hours following a period of profuse diarrhea.

The presence of an ileus means that orally or enterally administered medications will not adequately transit through the gastrointestinal tract to reach the distal colon.

Select the optimal pharmacologic regimen based on severity and anatomical barriers.

The correct regimen requires intravenous metronidazole for systemic coverage, enteral vancomycin for the proximal colon, and rectal vancomycin (via enemas) to ensure drug delivery to the distal colon.

This combination overcomes the transit barrier created by the ileus while aggressively treating the fulminant infection.

Key Concept

Fulminant Clostridioides difficile infection complicated by an ileus requires treatment with enteral vancomycin, intravenous metronidazole, and rectal vancomycin enemas.

Alternative Method

In cases where an ileus is severe and rectal administration is not tolerated or effective, surgical consultation for a diverting loop ileostomy with colonic lavage (often using polyethylene glycol and vancomycin) is an alternative to subtotal colectomy.

Estimated Time:1m 30s

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Alternative Method

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