The purpose of this study is to evaluate the safety, tolerability and pharmacokinetics (PK) of single and multiple ascending doses of fidaxomicin in healthy subjects. This study will also compare the safety, tolerability and PK of single and multiple doses of fidaxomicin in healthy Japanese and Caucasian subjects.

Eligible subjects will check into the unit on Day-2 and remain confined to the clinical unit until Day 17.

Cohorts 2 and 3, which may run in parallel, will only be enrolled after review of the available safety data of Cohort 1 by the Safety Review Team.

Inclusion Criteria:

1. Male subject and their female spouse/partners who are of childbearing potential must be using highly effective contraception consisting of two forms of birth control (one of which must be a barrier method) starting at Screening and continuing throughout the study period and for 90 days after final study drug administration

2. Male subject must not donate sperm starting at Screening and throughout the study period and for at least 90 days after final study drug administration

   Inclusion Criteria for Japanese Subjects

3. The subject is a healthy Japanese male who maintains the Japanese lifestyle, including diet and has a body mass index (BMI) of 18.0 to 28.0 kg/m2, inclusive.

   Inclusion Criteria for Caucasian Subjects

4. The subject is a healthy Caucasian male and has a BMI of 18.0 to 32.0 kg/m2, inclusive

Exclusion Criteria:

1. The subject has any clinically significant disease history
2. The subject has a history of or current C.difficile infection or history of stomach or intestinal surgery or resection that would potentially alter absorption and/or excretion of orally administered drugs (history of appendectomy, hernia repair, and/or cholecystectomy is permitted)
3. The subject has any clinically significant abnormality
4. The subject has a resting (i.e., seated for 5 minutes) pulse <40 or >90 beats per minute (bpm) at Screening or Day -2
5. The subject has hypertension (defined as seated systolic blood pressure [SBP] >140 mmHg or seated diastolic blood pressure [DBP] >90 mmHg) or hypotension (defined as seated SBP <90 mmHg or seated DBP <50 mmHg) at Screening or Day -2
6. The subject has/had a symptomatic, viral, bacterial (including upper respiratory infection), or fungal (non-cutaneous) infection within 1 week prior to clinic check-in on Day -2
7. The subject has a history of chronic diarrhea or constipation
8. The subject has a positive result for hepatitis C antibodies or hepatitis B surface antigen at Screening or has a known positive history of human immunodeficiency virus (HIV)
9. The subject has a known or suspected allergy or hypersensitivity to any of the components of fidaxomicin, the macrolide antibacterial class of compounds, or a history of multiple and/or severe allergies to drugs or foods or a history of severe anaphylactic reactions