The non-investigational reference therapies, Metronidazole, Vancomycin and fidaxomicin , are FDA-approved antibiotics currently in use today because of their effectiveness in suppressing the growth of C. difficile and therefore quickly eliminating the colitis and diarrhea. However, they do not promote the restoration of the normal bacterial flora. Therefore, when medication is stopped, the C. difficile colitis returns. In vitro findings have established that ursodeoxycholic acid is a surrogate for deoxycholic acid in preventing the growth of C. difficile, and interrupting recurrence.