Natalizumab is an injectable drug that is very effective in people with relapsing-remitting MS. However, it comes with a rare, but serious, risk of developing a brain infection called progressive multifocal leukoencephalopathy (PML). This risk is higher in people who test positive for the John Cunningham virus (JCV).

When neurologists assess and monitor the risk of natalizumab injections in a person with relapsing remitting MS, they may need to switch people who test positive for JC virus to another drug in order to reduce the risk of PML.

A Swedish study with 256 people with MS (who tested positive for JCV) looked at the effectiveness and tolerability of two alternatives to natalizumab: rituximab (an injectable drug) and fingolimod (an oral tablet). They found that rituximab was more effective in reducing later relapses, and had less reported side effects than fingolimod.

The results of this study provide important information to help people with MS and their neurologists make decisions about which treatment is right for them. However, more studies using different designs (for example blind drug trials) are needed before these results can be used as guidelines.

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