Cladribine (marketed under the brands Leustatin, Litak, and Movectro) is a therapy regularly used to treat leukemia but is currently being tested as a potential treatment for relapsing-remitting multiple sclerosis (RRMS). The therapy works by reducing the number of immune cells in the body, which should reduce damage to myelin caused by the disease.

Studies involving cladribine for RRMS

Cladribine has already passed through several rounds of testing. The results of a Phase 3 study, which involved more than 1,300 people with RRMS, were first published in 2010. The study compared two doses of cladribine with a placebo (NCT00213135). Both doses reduced the relapse rate by over 50 percent. Results from an extension  to the study (NCT00641537) showed that the effects of cladribine on relapse rates were maintained after two years of follow-up.

Another Phase 3 study, Oracle (NCT00725985), included 616 participants. It showed that taking cladribine after an initial demyelinating event delayed the onset of MS.

In June 2011, the U.S. Food and Drug Administration (FDA) concluded that the CLARITY study provided evidence of cladibrine effectiveness, but the agency also sought an improved understanding of safety risks and overall benefit-risk profile. Following FDA feedback, Merck KGaA announced the decision to no longer pursue the global approval process of cladibrine for RRMS treatment. This decision was not based on a changes to the benefit or risk profile of cladibrine, which remains the same.

An ongoing prospective observational long-term safety registry of people with MS who have participated in cladribine studies (NCT01013350) is estimated to end in late 2018.

Common cladribine side effects include infections, headaches, and cold symptoms.

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