Study to Evaluate the Pharmacokinetics of Fidaxomicin in Inflammatory Bowel Disease (IBD) Subjects With Clostridium Difficile Infection (CDI)

Inclusion Criteria: * Confirmed diagnosis or history of IBD for at least 3 months * Subject has have active IBD defined by : * partial MAYO score (ulcerative colitis subjects) of 2 or more, where at least 1 point has to originate from blood in stool * Harvey-Bradshaw Index (HBI) (Crohn's disease subjects) of 5 or more, excluding points for complications * CDI confirmed positive according to local standard testing for the presence of C. difficile within 48 hr prior to enrollment * Female subject is not breastfeeding at Screening or while participating in this study * Subject agrees to practice effective birth control from Screening and while participating in this study * Subject agrees not to participate in another interventional study while participating in this study * Male partner agrees not to donate sperm starting at screening and throughout the investigational period. Exclusion Criteria: * Subject has received more than one day of dosing of any CDI therapy within the 48 hrs prior to enrollment * Subject is unable to swallow oral study medication * Presence of an ostomy or short bowel syndrome * Subject has a current diagnosis of toxic megacolon * Subject is not willing to adhere to the provisions of treatment and observation specified in the protocol * Subject has been enrolled into this study previously, has taken any investigational drug within 28 days or 5 half-lives, whichever is longer, prior to enrollment, or is currently participating in another clinical study which may influence the assessment of efficacy and/or safety endpoints of this study, in the opinion of the Sponsor * Subject has previously participated in a CDI vaccine study * Subject has hypersensitivity to FDX or any of its components * Subject has a condition which, in the Investigator's opinion, makes the Subject unsuitable for study participation