**Core Concept**
Clostridium difficile (C. difficile) is a Gram-positive, spore-forming bacterium that can cause severe diarrhea and colitis, particularly in hospitalized patients. The management of severe C. difficile infection involves a combination of antibiotics and supportive care to prevent complications.

**Why the Correct Answer is Right**
The management of severe C. difficile infection typically involves the use of oral vancomycin, metronidazole, or fidaxomicin to target the bacteria. Vancomycin is a lipoglycopeptide antibiotic that inhibits cell wall synthesis in C. difficile, while metronidazole is a nitroimidazole antibiotic that damages the DNA of the bacteria. Fidaxomicin is a macrocyclic antibiotic that inhibits RNA synthesis in C. difficile. **Option B:** Fecal microbiota transplantation (FMT) is a promising treatment option for recurrent C. difficile infection, but it is not typically used for the initial management of severe disease.

**Why Each Wrong Option is Incorrect**
**Option A:** Intravenous vancomycin is not effective for the treatment of C. difficile infection, as it is not absorbed orally and therefore does not reach therapeutic levels in the gut.
**Option C:** Rifaximin is an antibiotic that is used to treat traveler's diarrhea and other gastrointestinal infections, but it is not effective against C. difficile.

**Clinical Pearl / High-Yield Fact**
Fecal microbiota transplantation (FMT) has been shown to be effective in treating recurrent C. difficile infection, but it is not without risks, including the transmission of other gastrointestinal pathogens.

**Correct Answer:** **Option A:** Intravenous vancomycin is not effective for the treatment of C. difficile infection.