A Safety and Efficacy Study of Oral Cladribine in Subjects With Relapsing-remitting Multiple Sclerosis (RRMS) (CLARITY)

Inclusion Criteria: Male or female, between 18 and 65 years of age (inclusive, at time of informed consent) Has definite MS according to the McDonald criteria Has relapsing-remitting disease with 1 or more relapses within 12 months prior to Study Day 1 Must have been clinically stable and not has a relapse within 28 days prior to Study Day 1 Has MRI consistent with MS at the pre-study evaluation according to the Fazekas criteria Has a EDSS score from 0 to 5.5, inclusive Weighed between 40-120 kilogram (kg), inclusive If female, she must: be post-menopausal or surgically sterilized; or uses a hormonal contraceptive, intra uterine device, diaphragm with spermicide, or condom with spermicide, for the duration of the study; and be neither pregnant nor breast-feeding If male, he must be willing to use contraception to avoid pregnancies Be willing and able to comply with study procedures for the duration of the study Voluntarily provides written informed consent, and for United states of America (USA) sites only, a subject authorization under Health Insurance Portability and Accountability Act (HIPAA) Exclusion Criteria: Has secondary progressive MS (SPMS) or primary progressive MS (PPMS) Prior use of disease modifying drugs (DMDs) within the last 3 months, or 2 or more prior treatment failures with DMDs on the basis of efficacy Has significant leukopenia (white blood cell count less than 0.5 times the lower limit of normal of the central laboratory) within 28 days prior to Study Day 1 Has received cladribine, mitoxantrone, total lymphoid irradiation, myelosuppressive therapy, campath-1h, cyclophosphamide, azathioprine, methotrexate or natalizumab Has received oral or systemic corticosteroids or adrenocorticotropic hormone within 28 days prior to Study Day 1 Has compromised immune function or infection Has received oral or systemic corticosteroids or adrenocorticotropic hormone within 28 days prior to Study Day 1 Has received cytokine-based therapy, intravenous immunoglobulin therapy, or plasmapheresis within 3 months prior to Study Day 1 Has platelet and absolute neutrophil counts below the lower limit of normal range within 28 days prior to Study Day 1 Has prior or current history of malignancy Has a history of persistent anemia, leukopenia, neutropenia, or thrombocytopenia after immunosuppressive therapy Has systemic disease that, in the opinion of the Investigator, might interfere with subject safety, compliance or evaluation of the condition under Study (for example, insulin-dependent diabetes, Lyme disease, clinically significant cardiac, hepatic, or renal disease, Human Immunodeficiency Virus, or Human T-Cell Lymphotrophic Virus Type-1) Has a psychiatric disorder that, in the opinion of the Investigator, was unstable or would preclude safe participation in the study Has allergy or hypersensitivity to gadolinium, to cladribine or any of its excipients Has used any investigational drug or experimental procedure within 6 months prior to Study Day 1