Natalizumab is a treatment for highly active relapsing MS. Its brand name is Tysabri.

Who can take natalizumab?

Natalizumab is recommended for the treatment of 'highly active' relapsing MS.

You can take natalizumab if:

  • you have relapsing MS and you've had a relapse in the past year and MRI scans show new signs (lesions) that your MS is active despite taking another DMT
  • you have relapsing MS and - whether or not you've taken another DMT - you've had at least two relapses in the last year and MRI scans show new signs (lesions) that your MS is active

How does natalizumab work?

Your immune system makes special types of cells to kill viruses and bacteria. But in MS these cells are thought to target nerves in your brain and spinal cord by mistake. Natalizumab kills these cells (called T cells) before they get into your brain and spinal cord where they would attack the covering (myelin) around the nerves there.

Natalizumab is given through a drip (known as an infusion), which takes about an hour, with another hour for you to be monitored. You need to go to hospital once every four weeks for the infusion, but you don't need to stay overnight.

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How well does natalizumb work?

MS drugs can be put into three groups based on how well they control it. The effectiveness of natalizumab is classed as 'high', the best of the the three groups. This is based on how much it reduces relapses and slows down how fast people's disability gets worse.

Relapses dropped by: 68%

This means that in a trial, on average, people saw a 68% drop in the number of relapses they had. This was compared to people who took a placebo, a dummy treatment with no drug in it.

Disability getting worse was slowed down by: 42%

This means that in a trial, on average, people saw a 42% drop in the risk of their disability getting worse. This was compared to people who took a placebo.

What are the side effects of natalizumab?

Compared to other DMTs the risk of side effects, especially serious ones, is among the highest.

After an infusion you might get these for a while: hiives (itchy skin), headache, shivers, stomach upset, joint pains, sore throat, or feeling sick, tired or dizzy. 


Being treated with natalizumab can increase your chances of developing a rare viral brain infection called PML (progressive multifocal leukoencephalopathy). Up to one in four who get PML can die. 

The risk of getting PML is small. Four in every thousand people who take natalizumab get it. By July 2016 around 600 people on natalizumab had got PML (out of over 140,000 people across the world taking this drug). 

Having a virus called the JC virus makes your risk of getting PML higher. Only one in 10,000 people who don't have this virus get PML. If you do have it one in 500 people at the highest risk get PML in the first two years of being on natalizumab. After that the risk goes up a lot. If your risk of PML is high your MS specialist will change your treatment, perhaps switching you to another DMT.

If you take natalizumab you'll get blood tests that look for the virus that causes it. If you're at risk of PML you'll be checked for early signs if it. Your MS team will tell you what to look out for and what to do if you notice signs of PML.

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Page last updated: 07 Sep 2016

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