Current and emerging therapies for the treatment of multiple sclerosis: focus on cladribine.

Multiple Sclerosis (MS) is a chronic inflammatory, immune-mediated, demyelinating disorder of the central nervous system with a heterogeneous clinical presentation and pathology in which activated lymphocytes play an important role in mediating tissue damage. Until recently, all first line therapies for MS were injectable. Several oral medications have been studied for preventative treatment of MS. Cladribine (2-chlorodeoxyadenosine) is a purine nucleoside analog that has been used for the treatment of several hematologic neoplasms, with a unique lymphcytotoxic mechanism of action. Cladribine has been investigated as treatment of MS for more than 15 years. A recent placebo-controlled, double-blind study of cladribine, CLARITY, showed decreased relapse rates, risk of disability progression and MRI measures of disease activity at 96 weeks. Cladribine's strengths included high efficacy and convenient, biannual oral dosing. However, concerns about safety prevented the FDA from approving cladribine in 2011. Thus, use of cladribine for treatment of relapsing and remitting multiple sclerosis will remain off-label.