Clemastine (also known as clemastine fumarate, Tavist, meclastine fumarate and mecloprodin fumarate) is a tablet that is currently used as an antihistamine. It is being developed as a potential treatment for relapsing remitting MS.

Current phase of trial: phase 2

Type of MS: Relapsing remitting MS.

How does clemastine work?

Clemastine is an active ingredient in antihistamines and works by reducing the effects of histamine that are associated with an allergic reaction. It is also used to relieve itching associated with chickenpox or eczema.

Clemastine enters the brain and causes drowsiness, so it is known as a sedating antihistamine. The treatment has been shown to suppress the immune system both in mice and healthy volunteers. This suggests that it could reduce the damage to myelin in MS by reducing the activity of immune cells.

Clemastine has also been shown to promote myelin repair in mice with a condition similar to MS. This is by using an innovative myelin repair screen developed in the USA.

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How is clemastine taken?

As a tablet or as a liquid that is taken orally.

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Latest research

The ReBUILD trial

This phase 2 trial involving 50 people with relapsing remitting MS ran for five months in the USA.

The trial participants will be split into two groups. One group will receive 4mg of clemastine twice a day alongside their usual DMT for three months, and will then switch to a placebo alongside their usual DMT for two months. The other group will take a placebo alongside their usual DMT for three months, and then switch to taking 4mg clemastine twice a day alongside their usual DMT for two months.

The main purpose of the trial is to assess clemastine as a potential remyelinating agent for people affected by relapsing remitting MS. This will be achieved by measuring improvements in vision as measured by MRI.The trial will also test how well the drug is tolerated.

Initial results from the study were announced at a scientific conference in April 2016. Researchers found that clemastine was able to improve the speed at which messages were transmitted from the eye to the brain. While these results have yet to be published, and the improvement itself was small, they highlight the potential that clemastine could have to repair myelin damage in MS.

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Earlier research

A small phase 1 trial completed in 2010 suggested that clemastine could suppress the immune response. The researchers found that the immune cells in 10 healthy volunteers injected with 2mg clemastine were less active than in volunteers given a placebo.

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What are the side effects of clemastine?

Clemastine has not been widely tested in people with MS so its side effects specifically for people with MS are not yet known. However, when used to treat allergy symptoms, side effects include drowsiness and fatigue, dizziness, and sometimes headaches, dry mouth, and nausea.  

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How does clemastine compare with current therapies?

Clemastine has not been directly compared with different therapies for the treatment of MS, therefore it isn’t currently possible to draw conclusions about its relative effectiveness at this time.

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When is clemastine likely to become available?

Clemastine is already licensed for other conditions but will need to undergo larger phase 2 and phase 3 trials to definitively test its effectiveness in MS. This process will take several years.

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