A 29-year-old presents with prolonged watery diarrhea after clindamycin. Hemodynamically stable. Normal WBC and creatinine indicate nonsevere CDI; first-line therapy is fidaxomicin 200 mg BID for 10 days (or vancomycin 125 mg QID). Severe disease would have WBC ≥15k or creatinine >1.5× baseline. Fulminant disease requires vancomycin (PO/NG) plus IV metronidazole. IV vanco is ineffective. Antimotility agents alone are contraindicated.