Comment MD here... (Score 4, Informative) 135
These are for patients who have recurrent C. diff, who have already failed PO vancomycin or fidaxomycin (difficid). Those are the only two antibiotics we really have after you fail metronidazole therapy. It's not an issue of strongness; it's penetrating into encysted bacteria which vancomycin does fairly poorly, and fidaxomycin does only moderately better. At that point, options are fecal therapy, another round of vanc or difficid with increasingly diminishing returns, or in severe cases, colectomy.