In this 96-week, placebo-controlled trial, oral cladribine reduced relapse rates and lowered the risk of sustained disability in patients with relapsing–remitting multiple sclerosis. Patients who were treated with cladribine had large reductions in lymphocyte counts and more infections, including herpes zoster and one death from reactivation of tuberculosis. Oral cladribine reduced relapse rates and lowered the risk of sustained disability in patients with relapsing–remitting multiple sclerosis. Patients had large reductions in lymphocyte counts and more infections, including herpes zoster and one death from reactivation of tuberculosis. Multiple sclerosis is a chronic and debilitating autoimmune disorder of the central nervous system, in which T and B cells are believed to play a major pathophysiological role. 1 – 3 Treatment benefits and disease modification can be obtained with the currently approved parenteral immunomodulatory and immunosuppressant therapies: interferon beta, glatiramer acetate, mitoxantrone, and natalizumab. However, treatment responses are often less than complete, and concern regarding safety and side-effect profiles may limit the general use of these drugs. The need for parenteral administration may present relative or absolute barriers to access, limiting treatment adherence and long-term outcomes. 4 Intracellular accumulation of the active . . .