**Core Concept**
Pseudomembranous colitis, also known as Clostridioides difficile (C. difficile) infection, is a bacterial infection of the colon that can cause severe diarrhea and colitis. The treatment of choice involves antibiotics that are effective against C. difficile.

**Why the Correct Answer is Right**
Vancomycin is the preferred treatment for Pseudomembranous colitis caused by C. difficile. It works by inhibiting cell wall synthesis in the bacteria, ultimately leading to bacterial death. Vancomycin is not absorbed from the gastrointestinal tract, which makes it ideal for treating C. difficile infections in the colon. The oral administration of vancomycin allows it to act locally in the colon, reducing the risk of systemic side effects.

**Why Each Wrong Option is Incorrect**
**Option A:** Metronidazole is sometimes used as an alternative treatment for mild cases of C. difficile infection but is not the first-line treatment due to its lower efficacy compared to vancomycin.
**Option B:** Ciprofloxacin is a broad-spectrum antibiotic that is not effective against C. difficile and may even contribute to the development of antibiotic-associated diarrhea.
**Option C:** Amoxicillin is a broad-spectrum antibiotic that is not effective against C. difficile and may even contribute to the development of antibiotic-associated diarrhea.

**Clinical Pearl / High-Yield Fact**
The use of proton pump inhibitors (PPIs) can increase the risk of C. difficile infection by altering the normal gut flora. Patients taking PPIs for an extended period should be monitored for signs of C. difficile infection.

**Correct Answer: C. Vancomycin.**