Natalizumab (Tysabri and Tyruko)

Jump to:

• Who can take natalizumab (Tysabri and Tyruko)?
• How do you take natalizumab (Tysabri and Tyruko)?
• How does natalizumab (Tysabri and Tyruko) work?
• How well does natalizumb (Tysabri and Tyruko) work?
• Natalizumab (Tysabri and Tyruko) side effects
• What tests do you need with natalizumab (Tysabri and Tyruko)?
• Stopping natalizumab (Tysabri and Tyruko)
• Natalizumab (Tysabri and Tyruko) and pregnancy, breastfeeding and contraception

Who can take natalizumab (Tysabri and Tyruko)?

You can have natalizumab (Tysabri and Tyruko) if you have relapsing MS that’s very active.

Across the UK this usually means you have two or more disabling relapses in a year. You also have new signs on your MRI scans that your MS is active. This will be lesions that are new, active or growing. 

In Scotland you can also have this drug if you’ve had one significant relapse in the last year despite taking a DMT. 

In England and Wales, similar guidance will apply from early 2026. NICE (the National Institute for Health and Care Excellence) published this new guidance in January 2026. It means the NHS should also offer natalizumab if: 

• you’ve had one significant relapse in the last year despite taking a DMT

  and

• cladribine (Mavenclad), another DMT, isn’t suitable for you

The recommendations will probably take a few months to be introduced in each local area in England and Wales. 

Northern Ireland usually decides about NICE guidance once it’s published.

Before 2024 doctors gave their patients Tysabri. Now you might get Tyruko, the ‘biosimilar’ version of the drug. 

Evidence from a drug trial shows Tyruko works just as well as Tysabri. If you’re already on Tysabri, you could be switched to Tyruko. But it’s not yet being used everywhere in the UK and might not be introduced in all places. 

Read more on the relationship between Tysabri and Tyruko, and moving from Tysabri to Tyruko

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How do you take natalizumab (Tysabri and Tyruko)?

You usually have natalizumab (Tysabri and Tyruko) as an infusion (or ‘drip’) in a hospital. The drug is pumped through a needle into a vein in your arm. This takes an hour, then, after another hour of monitoring, you go home.

You usually have natalizumab every four weeks. If you’re pregnant, you might have it every six or eight weeks. People at risk of a serious side effect called PML may have the drug every six weeks. This reduces the risk of PML a lot.

With Tysabri you can also have the drug as an injection under the skin, usually every four weeks. Once you’ve had six doses without any problems, you don’t need to go to a hospital for your dose of Tysabri. A nurse can inject you at home, for example. Injections take less time than infusions. Tyruko isn’t available as an injection.

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How does natalizumab (Tysabri and Tyruko) work?

Natalizumab (Tysabri and Tyruko) works by targeting B and T cells. These are special types of white blood cells in your immune system. It’s thought that these cells cause a lot of the damage in MS. They normally kill viruses and bacteria that get into your body. But in MS they attack and damage myelin. That’s the protective covering around nerves in your brain and spinal cord.

Natalizumab (Tysabri and Tyruko) is a monoclonal antibody drug. These artificial antibodies are made in a laboratory. Any DMT that ends with ‘mab’ is one of these drugs. 

With this drug these antibodies stick to the surface of B and T cells. This keeps them in your bloodstream and stops them getting into your brain and spinal cord. That means they can’t damage nerves there, so you get relapses much less often. 

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How well does natalizumb (Tysabri and Tyruko) work?

The effectiveness of natalizumab (Tysabri or Tyruko) is classed as 'high'. Each DMT can be rated as ‘moderate’, ‘good’ or ‘high’. This is based on how much it can reduce relapses and slow down disability getting worse.

Monoclonal antibody drugs like natalizumab (Tysabri or Tyruko) are some of the DMTs with the best results against MS. 

Natalizumab got the go-ahead in 2007 for use on the NHS based on a trial called AFFIRM. In this trial they compared natalizumab with a placebo, a dummy treatment with no drug in it.

In that trial…

Relapses dropped by: 68%

This means that after this two year long trial, on average, people saw a 68% drop in their number of relapses. This was compared to people who took the placebo. 

Disability getting worse was slowed down by: 42%

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

In this trial there was also a 92% reduction in the number of new lesions (areas of damage in the brain or spinal cord). This was compared to people who took the placebo.

Some people who take natalizumab see some improvement in their level of disability (as measured by their EDSS score.) 

The original trials of natalizumab were of Tysabri. A trial of Tyruko called ANTELOPE showed that it worked as well as Tysabri.

How well does natalizumab (Tysabri and Tyruko) work over many years?

Natalizumab continues to work well over many years. Studies have followed people for up to 15 years. A Danish study followed 2,424 people for 13 years. Their relapses dropped by 72%. In a study over 15 years people’s relapses dropped on average by 92%. This was compared to how many relapses they had the year before they started the drug. Seven in ten people didn’t see their level of disability get worse over ten years.

Long-term studies have found no new side effects that doctors didn’t already know about. The main reason people stop taking natalizumab is because their risk of PML gets too high. This is a rare but very serious brain infection. 

Read more about PML

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Natalizumab (Tysabri and Tyruko) side effects

Side effects of natalizumab (Tysabri and Tyruko) are similar to the side effects you get with other very effective DMTs. Some are harder to manage than others.

Common (up to 1 in 10 people get them) and very common side effects (more than 1 in 10 people get them): 

After an infusion, around one in ten people get a short-lived reaction with:

• hives (an itchy skin rash)
• headache
• shivers
• stomach upset
• joint pains
• sore throat
• feeling sick, tired or dizzy

Other common side effects include infections of your urinary tract, lungs, nose and throat. These may affect up to one in ten people. 

More serious side effects

About one in 25 people have a more serious allergic reaction with:

• hives
• swelling of your face, lips or tongue
• difficulty breathing
• chest pain
• fever
• feeling flushed (your face and chest go red)

One in a hundred get an even more severe allergic reaction.

A year-long trial of 265 people compared Tyruko with Tysabri. It found no significant differences in side effects between them. 

But there’s evidence that some people react in a different way to Tyruko than they do to Tysabri. If you experience new side effects with Tyruko, you should report them on the Yellow Card Scheme and speak to your neurologist. 

Read more about moving from Tysabri to Tyruko

PML: a rare side effect of natalizumab (Tysabri and Tyruko)

PML is short for progressive multifocal leukoencephalopathy. It’s a very serious brain infection that can kill around a quarter of the people who get it. It’s caused by the John Cunninghan (JC) virus. Natalizumab affects the immune system, so this can let the JC virus become active. That can trigger PML.

When taking this drug your risk of getting PML in any one year can range from around 1 in 100 to 1 in 10,000. This will depend on things like how long you take the drug, and whether you have the JC virus or not. The risk of PML is the main reason why people stop taking this drug.

You need to have the JC virus to be at any real risk of PML. And the risk of PML goes up the longer treatment with natalizumab goes on. After two years your neurologist may need to take steps to manage your risk of PML. Your risk is also higher if you’ve taken a drug in the past that suppressed your immune system.

If the JC virus infects you, your body makes antibodies to fight it. A blood test shows if you have these antibodies, and whether you have low or higher levels of them.

You can still take natalizumab if you have the JC virus, as long as your antibody levels are below a certain level. Low levels mean your immune system is keeping the virus under control and there isn’t enough of it to trigger PML. Higher levels are a sign that you have active JC virus infection. Your neurologist will then take steps to reduce your PML risk.

Once antibody levels go over a certain point, you may need to switch to a different DMT. Or your doses of natalizumab might change to every six weeks instead of every four. This makes a very big difference to your risk of PML.

Blood tests every six months will check your levels of JC virus antibodies. These results help your neurologist work out your risk of PML. That way, they know when to take action. 

If your PML risk is high enough, you’ll have regular MRI scans to look for early signs of PML. Your MS team will tell you what PML symptoms to look out for, and what to do. The risk of PML is the same with both Tysabri and Tyruko.

Read more about PML

Find out more about all the possible side effects of natalizumab

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Stopping natalizumab (Tysabri and Tyruko)

You should never stop taking a DMT without telling your doctor. With some DMTs there’s a risk of ‘rebound’ if you suddenly stop. This is when your MS gets much worse within a few weeks or months. Natalizumab (Tysabri and Tyruko) is one of the DMTs with the biggest risk of rebound.

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What tests do you need with natalizumab (Tysabri and Tyruko)?

Tests before treatment begins

Before treatment starts, you have an MRI scan of your brain. Your neurologist will compare this scan with ones you have later to see if your DMT is working. 

Tests on your blood and pee will check that your liver and kidneys are working normally. A blood test will find out if you have the JC virus that’s linked to the brain infection PML.

Vaccination

Like most DMTs, this drug makes infections more likely. Before you start it, your neurologist will check if you have protection against some of the infections it puts you at risk of. 

Your neurologist will check you’re up to date on your vaccines. This includes childhood ones like chickenpox (that vaccine protects you against shingles) and the MMR vaccine for measles, mumps and rubella. Some ‘live’ vaccines, like these two, aren’t safe to have once you’ve started many DMTs. Your MS team or GP can tell you whether a vaccine is ‘live’ or not. 

You’ll have any vaccines you need a few weeks before you start this drug. 

You can safely have the annual flu jab while taking this DMT. 

Read more about vaccines 

Tests during treatment

For an hour after each dose of natalizumab (Tysabri and Tyruko), someone checks your heart rate, temperature and blood pressure. This is in case you have a serious allergic reaction.

Regular blood tests will check how your liver is working. Every six months a blood test will look for the JC virus in case you’ve picked it up since your last test. The blood test also tells your neurologist how high your levels of antibodies to the JC virus are. This helps your doctor work out your PML risk and decide how often you might need MRI scans.

During the first five years of treatment, you should have at least one MRI scan a year. This will check how well the drug is controlling your MS. If you’re at risk of PML, regular MRI scans look for early signs of it. Scans could range from every three months to every six or 12 months depending on how big your risk of PML is.

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Natalizumab (Tysabri and Tyruko) and pregnancy, breastfeeding and contraception

Pregnancy

Natalizumab (Tysabri or Tyruko) doesn’t have a licence for use in pregnancy. But no studies have shown it harms unborn babies. The drug doesn’t cross the placenta from mother to baby during the first three months of a pregnancy.

If you want a baby but need a very effective DMT, your neurologist may suggest you switch to natalizumab. If you’re planning a pregnancy, this drug is one of the less risky DMTs. 

If you want to get pregnant, your neurologist may recommend you keep taking natalizumab through your pregnancy. This will avoid rebound, which is when your MS gets much worse within a few months of coming off a DMT.

During pregnancy the chances of a relapse can drop. But you can't rely on this natural protection if you’re on natalizumab. That’s because if you’re on natalizumab, it’s because your MS is more active than it is for most other people.

Some women choose to carry on with their infusions until around week 34 of their pregnancy. They then start it again within eight to 12 weeks of the baby’s birth to avoid rebound. Instead of every four weeks, infusions can be every six or eight weeks during the pregnancy. The drug works just as well with infusions further apart.

If you want to have a child, discuss this with your neurologist. If you think you’ve become pregnant, let your medical team know at once. Never stop your DMT without first getting their advice.

Breastfeeding

UK experts think it’s unlikely a baby will take in any of the drug from breast milk.

Contraception

There are no special recommendations about contraception for people on natalizumab (Tysabri or Tyruko).

Read more about pregnancy, breastfeeding and contraception and DMTs

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