Tysabri and Tyruko: is there a difference?

What are Tysabri and Tyruko?

Tysabri and Tyruko are different brands of natalizumab. Natalizumab is one of the most effective DMTs. People take it if their MS is very active.

Before 2024, only Tysabri was available. Since 2024 neurologists have sometimes given their patients the Tyruko brand of natalizumab instead. This is because it costs the NHS less. If you need natalizumab, you might get Tyruko rather than 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. 

Are there any differences between Tysabri and Tyruko?

Tyruko is very like Tysabri, but it’s not 100% the same. Tyruko has the same type of active ingredient as Tysabri. A drug trial compared the two brands and found that Tyruko worked as well as Tysabri.

Tysabri was the original brand of natalizumab. Tyruko is a new version of it called a ‘biosimilar’. A ‘biosimilar’ is a copy of a ‘biological’ drug. Most drugs are made from chemicals. But biological drugs, like natalizumab, are made from living organisms instead. These could be things like blood, bacteria, viruses, or cells from plants or animals.

Living organisms are always slightly different from each other. That's why a biosimilar version of a drug can never be an identical copy. But it will be very close to it.

Biosimilar drugs are not new. Doctors use them to treat other health problems like rheumatoid arthritis. Because they’re cheaper, more people can have them.

One big difference between Tysabri and Tyruko is in how you take them. You can take Tysabri as an infusion (a ‘drip’), but also as an injection given under the skin by a nurse. Tyruko is only available as an infusion.

Read more about the difference between biosimilar and branded versions of DMTs.

Does Tyruko work as well as Tysabri?

Evidence from a major trial shows Tyruko works as well as Tysabri. The ANTELOPE trial compared these two versions of natalizumab. It showed that Tyruko worked as well as Tysabri and was as safe. 

People on Tyruko saw a similar drop in relapses. They also had a similar reduction in lesions (areas of damage in the brain or spinal cord). Their disability slowed down at a similar rate, too. There were no significant differences in side effects.

People who switched from Tysabri to Tyruko saw no difference in how well their treatment worked.

Most people who've switched from Tysabri have had no problems. But there is evidence that some people react in a different way to Tyruko than they do to Tysabri.

Speak to your MS team if you switch to Tyruko and notice changes to your MS, or if you have an unwanted or harmful reaction.

The MHRA, who gave the green light for the NHS to use Tyruko, are keeping an eye on side effects and how well it works. Some people have had problems with Tyruko, so the MHRA has been doing extra monitoring. They’re looking closely at all the information they have on natalizumab (Tyruko and Tysabri). And they're speaking to independent experts.

They’re working with the company that makes Tyruko so that they can collect more data. This will help us understand why some people react to Tyruko in a different way, when most people don’t.

The MHRA has looked at the information available. There's no evidence so far that Tyruko works less well or causes disability. But the MHRA will keep checking this.

What should I do if I have issues or concerns about Tyruko?

Your neurologist can answer your questions or worries about taking Tyruko. So can a member of your MS team. Speak to them if you notice any changes to your MS. Let them know if you have an unwanted or harmful reaction after changing your drug.

If you have a side effect to natalizumab (Tysabri and Tyruko), it’s important you report this. You can do this through the MHRA’s Yellow Card scheme.

You and the person who prescribes the drug, can both record any side effects. Make it clear if you’re taking Tyruko or Tysabri. Give any details you have about your levels of JC virus antibodies. Let them know your treatment history.

The MHRA looks at its Yellow Card reports every week, so they might contact you for more details.

You can also call our MS Helpline on 0808 800 8000 or email [email protected]

Do I have to use Tyruko instead of Tysabri?

NHS England encourages doctors to make the switch from Tysabri to Tyruko a shared decision with their patients. This means you should get information about what’s changing. Then you make the decision together.

But shared decision making doesn’t mean you can expect to stay on Tysabri. That’s because Tysabri and Tyruko are seen as ‘interchangeable’. This means experts believe they work as well and have the same side effects.

If you notice unwanted changes while on Tyruko, your MS team will look again at your treatment. Together you may decide another drug would be better for you. If your neurologist agrees, this should include the option of going back to Tysabri.

The MHRA gives guidance to doctors about biosimilar drugs like Tyruko. If your doctor prescribes you a biosimilar drug, the brand name should be on the prescription. So you can check your prescription to see which version of the drug you’re getting.

Someone in your MS team, including your neurologist, can answer your questions about switching to Tyruko from Tysabri.

Is the risk of PML the same with Tysabri and Tyruko?

Yes, the risk of PML is the same for both Tysabri and Tyruko. PML is a rare but sometimes fatal side effect of natalizumab. But you only have a real risk of PML if you have a virus called the JC virus. Both brands of natalizumab carry some risk of PML if you have this virus.

A test for the JC virus can tell you if you have it. The test can also help your doctor work out how high your risk of PML is. 

Read more about PML

JC virus tests

A JC virus blood test will show if you’re at risk of PML. This is a rare but dangerous side effect of natalizumab (Tysabri and Tyruko). 

When your immune system comes across a virus for the first time, it makes antibodies to it. Antibodies help kill a virus. The JC virus test looks for antibodies in your blood to this virus, not for the virus itself.

A ‘positive’ test result means you’ve picked up the JC virus at some point. Your immune system has made antibodies to fight it. A ‘negative’ result means you don't have the virus.

Antibodies to the JC virus stay in your blood for years, maybe for life. If you’ve been infected, recently or long ago, the blood test will show you have antibodies. It also shows how high your levels of these antibodies are. Doctors call this your ‘JCV index’. They use it to work out your risk of getting PML.

Low levels of antibodies mean your immune system has the virus under control. That means your risk of PML is low.

Rising or high levels means the virus is active. Once levels reach a certain point, your risk of PML has got too high. Your neurologist will then talk to you about steps to take to avoid PML. You can read about what these might be on our PML page.

Whether you take Tysabri or Tyruko, you must have a JC virus test every six months. That way your neurologist can keep track of your antibody levels and your PML risk.

Do JC virus tests used with Tysabri and Tyruko give different results?

Yes. The two companies that make Tysabri and Tyruko make their own blood tests for the JC virus. These can give different results.

Some people switch from Tysabri to Tyruko, then find they test positive for JC virus. This is after being on Tysabri but testing negative for the virus.

If this happens to you, it's possible you picked up the virus since your last test. And the new test is now showing that. Out of every hundred people each year between 3 and 6 of them get infected with the virus.

But a change in your test result, or in the level of your antibodies, can happen even when nothing has changed. That’s because there seems to be a difference in how the two tests work. There’s a difference in how they detect levels of antibodies to the JC virus.

The ‘ImmunoWell’ test used with Tyruko seems to record higher levels of antibodies. That’s why a ‘positive’ result appears more likely with this test.

The Tyruko test can show higher antibody levels. That can make it harder for you and your doctor to work out your PML risk. That’s because PML risk guidelines are based on years of experience with results from the ‘Stratify’ test used with Tysabri.

There’s a chance that the test used with Tyruko might make your risk of PML seem higher than it is. Neurologists now have guidance on what this means for your treatment and monitoring. You may have extra JC virus tests, with MRI scans more often. Or your neurologist might suggest you take the drug every six weeks instead of every four. Or you might come off Tyruko and take another DMT instead.

One thing is important to know. Both tests are accurate if they come back with a ‘negative’ result. If that happens, you can be sure that you don’t have the JC virus.

Am I more likely to test positive for the JC virus if I take Tyruko?

Some people on Tyruko are more likely to get a 'positive' JC virus blood test result. That's compared to if they were on Tysabri. This isn't because of the drug, but because of differences between the tests used for both drugs.

The test used if you take Tyruko appears more likely to find antibodies to the JC virus. So it’s possible for these tests to give different results.

You might get a negative result with the test used with Tysabri. Or it could show you have lower levels of antibodies. But with the Tyruko test your result might be positive. Or it may show higher levels of antibodies. All this might happen despite nothing actually changing. It doesn’t mean your risk of getting PML must have gone up.

There's another explanation for a change in your test results. You've picked up the virus since your last test, and the new test is showing that.

What happens next with JC virus testing?

MS experts agree that it makes sense to keep using the Tyruko JC virus test for people on that drug. The ‘Stratify’ test used with Tysabri patients isn’t available for Tyruko patients to use.

From the summer of 2025 neurologists have new guidance to help them manage PML risk in patients on Tyruko.

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