Potential short-term use of oral cladribine in treatment of relapsing-remitting multiple sclerosis.

Multiple sclerosis (MS) is a chronic, immune-mediated disorder of the central nervous system. The clinical course of MS varies among patients. Currently, interferon (IFN) products, including IFN β-1a administered intramuscularly or subcutaneously and IFN β-1b subcutaneously, glatiramer acetate, natalizumab, and mitoxantrone are approved disease-modifying therapies for the treatment of relapsing-remitting MS. Cladribine, also known as 2-chlorodeoxyadenosine, is a synthetic adenosine deaminase-resistant purine nucleoside analog that preferentially depletes lymphocyte subpopulations. This sustained effect on lymphocytes is advantageous for patients with MS. CLARITY (CLAdRIbine Tablets Treating MS OrallY), a Phase III trial, has demonstrated that short-term oral cladribine decreases relapse rates and risk of disability progression in comparison with placebo. Cladribine was well tolerated in the study, with the most common adverse effects being headache, nausea, upper respiratory tract infections, and lymphocytopenia. An ongoing study is evaluating the efficacy and safety of the combination of oral cladribine and IFN-β products. A further ongoing study is examining the use of oral cladribine in clinically isolated syndrome and time to conversion to MS. Although the results of CLARITY are promising, the exact role of oral cladribine may be better defined with the completion of ongoing studies.