Cladribine to Treat Relapsing Forms of Multiple Sclerosis

Cladribine is a purine nucleoside analogue that selectively depletes peripheral lymphocytes without a major impact on cells of the innate immune system. An oral formulation of cladribine has been developed to be given as short courses over two annual cycles. Oral cladribine results in the peripheral depletion of lymphocytes that is gradual, occurring over several weeks, and is not associated with a cell lysis syndrome, has a greater impact on B cells than T cells, and is followed by gradual reconstitution of the peripheral lymphocyte counts over several months. Oral cladribine is effective in relapsing forms of multiple sclerosis. As a selective immune reconstitution therapy (SIRT), cladribine acts as a short-term immunosuppressant, relative to other maintenance immunosuppressive therapies that result in long-term immunosuppression. The main safety signal that has emerge relates primarily to herpes zoster infection, which was more common in patients with higher grades of lymphopenia, in particular grade 3 and 4 lymphopenia. Data from the oral cladribine extension trial and safety register, and reanalysis of the pivotal phase III trial has indicated that oral cladribine is unlikely to be associated with an increased short- to intermediate-term risk of malignancy.