Cladribine is used as an anti-cancer drug (Leustat). It's being investigated by Merck as an oral treatment for relapsing MS.

Current phase of trial: Under review by the European Medicines Agency (EMA).

Type of MS: Relapsing MS.

How does cladribine work?

In MS, the body’s own immune cells mistakenly attack the myelin that surrounds nerve cell fibres. Cladribine works by reducing the number of immune cells in the body, which should reduce the damage to myelin.

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How is cladribine taken?

Cladribine is taken as a tablet

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Latest Research

In 2011, Merck Serono announced that it was withdrawing cladribine from the approval process. This decision was based on concerns from the European Medicines Agency (EMA) about an increased risk of cancer and the drug’s effects on the immune system.

However, in September 2015 Merck announced that further research (including interim results from a follow-up registry) had shown that cladribine did not increase the risk of cancer compared to other licensed DMTs, and that they were restarting the application process for licensing. In July 2016 the EMA announced that they were reviewing the evidence.


Results from this phase 3 study involved more than 1,300 people with relapsing MS were published in 2010. The study compared two doses of cladribine (3.5 and 5.25mg/kg) to a placebo (dummy) drug. They showed that the higher dose of cladribine reduced the relapse rate by 55% and the lower dose by 58% compared to placebo.

Results from an extension study were announced in April 2016 at a conference. After two years of follow up, the effects of cladribine on relapse rates were maintained.

ORACLE study

Results from this phase 3 trial involving 616 people were published in March 2014. This trial aimed to investigate whether cladribine reduced the conversion to clinically definite MS after an initial demyelinating event. Researchers reported that taking cladribine delayed the onset of clinically definite MS.

Earlier studies

ONWARD study

This phase 2 study investigated the effectiveness of cladribine as an add-on to beta-interferon therapy in 200 people with relapsing and people with secondary progressive MS who are still experiencing relapses.

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What are the side effects of cladribine?

Side effects included headaches and symptoms of the common cold. Opportunistic infections, particularly herpes virus infections, were more common in people taking cladribine.

In 2011 there were concerns that cladribine might be linked with an increased cancer risk, but long term studies have shown that cladribine does not increase the risk of cancer compared to other licensed DMTs.

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How does cladribine compare with current therapies?

Cladribine hasn’t yet been directly compared with other therapies for the treatment of MS, so it isn’t possible to draw conclusions about its relative effectiveness.

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When is cladribine likely to become available?

Cladribine is being considered by the European Medicines Agency (EMA), who will decide if cladribine will be licensed for relapsing MS in Europe. We're not sure when this decision will be announced.

We'll keep you updated on the progress of cladribine.

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