Final answer:
The drug of choice to treat C. difficile is metronidazole. Vancomycin can also be used if specific criteria are met.
Step-by-step explanation:
The drug of choice to treat C. difficile is metronidazole. It is the preferred treatment option if the C. difficile diagnosis has been confirmed. However, if metronidazole is ineffective or if the patient meets certain criteria (e.g., under 10 years of age, pregnant, or allergic to metronidazole), vancomycin can be used.