A 72-year-old woman presents with 4 days of watery diarrhea, abdominal cramps, and fatigue. She recently completed a 7-day course of ciprofloxacin for a urinary tract infection. She denies fever but reports 8–10 episodes of foul-smelling, watery stools per day. On examination, she is mildly dehydrated. Lab work reveals: • WBC: 18,000/mcL (elevated). • Serum creatinine: 1.5 mg/dL (baseline: 0.8 mg/dL). • Serum albumin: 2.4 g/dL (low). Stool testing is positive for Clostridium difficile toxin B. Which of the following is the most appropriate initial treatment for this patient?
