4. A 61-year-old woman with limited ambulation and a history of cerebrovascular accident 5 years ago comes to your office with diarrhea. She has a history of depression and is on multiple medica- tions: venlafaxine hydrochloride, clopidogrel bisulfate, nifidepine, and hydrochlorothiazide. She was hospitalized for pyelonephritis, during which time she was treated with intravenous ceftriax- one sodium. Since discharge from the hospital, she tells you that she has had diarrhea for several months and has experienced a loss in weight of 8 kg in that time, although she has a good appetite and eats a balanced diet. On examination, she is afebrile, her blood pressure is 137/78 mm Hg, and her heart rate is 73 beats per minute. Laboratory test results show that her electrolytes, creatinine, complete blood count, and albumin are normal. A stool sample is cultured and revealsClostridium difficile toxin. The best initial treatment option for her C difficile-associated diarrhea is
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