A 72-year-old man is evaluated in the intensive care unit due to rapidly worsening abdomin… — USMLE Step 2 CK

A $72$ -year-old man is evaluated in the intensive care unit due to rapidly worsening abdominal distension and hemodynamic instability. He was admitted $8$ days ago for severe community-acquired pneumonia, which was treated with a $5$ -day course of intravenous levofloxacin. On hospital day $5$ , he developed frequent, foul-smelling, watery stools. Today, the nursing staff notes that his diarrhea abruptly ceased over the last $12$ hours, but he has become progressively lethargic. His temperature is $39.1^\circ\text{C}$ ( $102.4^\circ\text{F}$ ), pulse is $132\text{/min}$ , blood pressure is $82/48\text{ mm Hg}$ , and respirations are $26\text{/min}$ . Physical examination reveals a markedly distended abdomen that is tympanitic to percussion and diffusely tender with guarding. Bowel sounds are absent. Laboratory studies show a leukocyte count of $34,500\text{/mm}^3$ and a serum lactate of $4.6\text{ mmol/L}$ . Plain abdominal radiography demonstrates colonic dilation with a transverse colon diameter of $10.2\text{ cm}$ , loss of haustral markings, and no evidence of pneumoperitoneum. In addition to aggressive fluid resuscitation and urgent surgical consultation, which of the following is the most appropriate pharmacotherapy?

A
Intravenous vancomycin and enteral metronidazole
B
Enteral fidaxomicin monotherapy
C
Intravenous piperacillin-tazobactam
Enteral vancomycin and intravenous metronidazoleAnswer
E
Intravenous ceftriaxone and intravenous metronidazole

Answer

Enteral vancomycin and intravenous metronidazole

The correct intervention is the administration of enteral vancomycin alongside intravenous metronidazole. This patient's presentation of recent antibiotic use, initial watery diarrhea that abruptly ceased, profound leukocytosis, shock, and marked colonic dilation (

>6\text{ cm}

) is the classic picture of fulminant Clostridioides difficile infection complicated by toxic megacolon. When C. difficile progresses to an ileus (indicated by the cessation of diarrhea and absent bowel sounds), standard enteral monotherapy becomes inadequate because the lack of peristalsis prevents the drug from being reliably distributed throughout the colon. To overcome this, guidelines recommend adding intravenous metronidazole to enteral vancomycin (given orally, via nasogastric tube, or via enema). Metronidazole is uniquely beneficial in this setting because it is systemically absorbed and subsequently secreted directly into the inflamed colonic mucosa, ensuring therapeutic delivery independent of colonic transit.

Step-by-Step Solution

Analyze the clinical history and physical examination findings.

The patient developed watery diarrhea following antibiotic use, which progressed to absent bowel sounds, shock, and a massively dilated colon.

To diagnose fulminant Clostridioides difficile infection complicated by toxic megacolon and an ileus.

Determine the therapeutic requirements for this specific complication.

Standard monotherapy is inadequate; the patient requires aggressive dual pharmacotherapy.

The presence of an ileus prevents enterally administered medications from reliably traversing the entire gastrointestinal tract.

Select the appropriate pharmacological agents based on their pharmacokinetic profiles.

The optimal regimen is enteral vancomycin combined with intravenous metronidazole.

Enteral vancomycin achieves high luminal concentrations where it can reach, while intravenous metronidazole is actively secreted into the inflamed colonic mucosa, bypassing the arrested peristalsis.

Key Concept

Fulminant Clostridioides difficile infection complicated by toxic megacolon or an ileus requires dual therapy with enteral vancomycin and intravenous metronidazole due to altered gastrointestinal transit.

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