A 28-year-old man from Delhi presents with acute-onset severe abdominal pain, profuse watery diarrhea (15–20 stools/day), and fever 3 days after undergoing elective appendicectomy under general anesthesia. On examination, he is dehydrated and has diffuse abdominal tenderness. Stool is bloody. Flexible sigmoidoscopy shows pseudomembranes on the colonic mucosa. What is the most appropriate immediate next step?

Explanation

## Clinical Diagnosis: *Clostridium difficile* Colitis (CDI) **Key Point:** Pseudomembranes on sigmoidoscopy are pathognomonic for *C. difficile*-associated diarrhea (CDAD). The temporal relationship to antibiotic exposure (perioperative prophylaxis or therapeutic antibiotics) and the clinical picture of watery diarrhea with fever and leukocytosis confirm the diagnosis. **High-Yield:** *C. difficile* produces two exotoxins: - **Toxin A** (enterotoxin): causes fluid secretion and inflammation - **Toxin B** (cytotoxin): causes cytoskeletal damage and cell death Both toxins inactivate Rho GTPases, leading to loss of tight junctions and pseudomembrane formation. ## Management Algorithm for CDI ```mermaid flowchart TD A[Suspected CDI: diarrhea + pseudomembranes + antibiotic exposure]:::outcome --> B[Discontinue offending antibiotic ASAP]:::action B --> C{Severity?}:::decision C -->|Non-severe/Moderate| D[Oral vancomycin 125 mg QID × 10 days]:::action C -->|Severe/Fulminant| E[Oral vancomycin 125 mg QID + IV metronidazole]:::action D --> F[Send stool for toxin assay/NAAT]:::action E --> F F --> G[Monitor for recurrence]:::action G --> H{Recurrent CDI?}:::decision H -->|Yes| I[Fidaxomicin or vancomycin taper]:::action ``` **Clinical Pearl:** Discontinuation of the offending antibiotic is the FIRST and most critical step. Most cases resolve with antibiotic cessation alone. Vancomycin is preferred over metronidazole for moderate-to-severe disease because it achieves higher intraluminal concentrations and is not systemically absorbed. **Warning:** Loperamide and other antimotility agents are contraindicated — they increase the risk of toxic megacolon and perforation by allowing toxin to accumulate. ## Why This Answer Is Correct The immediate next step is to: 1. **Stop the offending antibiotic** — this removes the selective pressure for *C. difficile* overgrowth 2. **Start oral vancomycin** — the drug of choice for CDI (not metronidazole, which is reserved for mild disease) 3. **Send stool for toxin assay** — confirms diagnosis via toxin detection or NAAT (nucleic acid amplification test) This patient has bloody diarrhea and pseudomembranes, indicating at least moderate disease, warranting vancomycin (not metronidazole). [cite:Harrison 21e Ch 157; Robbins 10e Ch 8]