An MS monoclonal antibody
Natalizumab
A strong MS treatment given by drip or injection that reduces relapses, with a serious brain-infection (PML) risk linked to JC virus.
What is Natalizumab?
Natalizumab is a strong treatment for highly active relapsing multiple sclerosis, given as a drip into a vein or as an injection under the skin, usually every few weeks. It works by stopping immune cells from crossing into the brain and spinal cord, which markedly reduces relapses. Its most important risk is a serious brain infection called PML, caused by a common virus called the JC virus; testing for JC virus antibodies and careful risk counselling are central to using it safely. People are monitored closely, and any new weakness, vision, speech or thinking changes must be reported straight away.
Education and reference only. This is a plain-language guide to Natalizumab — it deliberately contains no doses. Doses depend on the person, the brand and the reason for treatment, and belong with your prescriber. Always check the BNF, the product labelling (SmPC) and follow medical advice.
What it is
Natalizumab is a monoclonal antibody used as a disease-modifying treatment for highly active relapsing multiple sclerosis. It is given regularly, either as an infusion into a vein or as an injection under the skin, in a setting where people can be observed. It is one of the more powerful MS treatments and is often used when the disease is very active or when other treatments have not controlled it. It reduces relapses substantially but does not cure MS.
How it works
Natalizumab blocks a molecule on immune cells that they use to cross from the bloodstream into the brain and spinal cord. By keeping these immune cells out of the central nervous system, it greatly reduces the inflammation that causes relapses and new damage on scans. The same action, however, can reduce the immune surveillance that normally keeps a common virus (the JC virus) in check, which is why it carries a risk of the serious brain infection PML. This is why JC virus testing and ongoing risk assessment are so important.
Company & origin
Originated / developed by: Biogen.
A monoclonal antibody given by infusion or injection in the UK for highly active relapsing multiple sclerosis.
Practical use
How to take Natalizumab
General, dose-free guidance — always follow your prescriber's and the leaflet's specific instructions.
- It is given by a healthcare professional as a drip into a vein or as an injection under the skin, usually every few weeks.
- Have your JC virus antibody test before starting and at intervals during treatment, as this guides your risk.
- Make sure you understand the PML warning signs and report new weakness, vision, speech or thinking changes urgently.
- Attend all your scheduled doses and monitoring appointments, including any planned scans.
- Tell your team about any infections, and about any previous immune-suppressing treatments you have had.
- Do not stop or switch treatment without specialist advice, as a plan is usually needed to manage the change safely.
Weighing it up
Advantages & disadvantages of Natalizumab
Advantages
- A highly effective treatment that strongly reduces relapses in active relapsing multiple sclerosis.
- Given at intervals rather than daily, with an injection-under-the-skin option as well as a drip.
- Often helps when other treatments have not controlled the disease.
Disadvantages
- Carries a serious risk of the brain infection PML, especially in people who carry the JC virus.
- Requires JC virus testing, careful risk counselling and close ongoing monitoring.
- Given in a clinical setting with observation, and can cause infusion or injection reactions.
Practical use
Good to know
Natalizumab is very effective, but its defining safety issue is the risk of progressive multifocal leukoencephalopathy (PML), a serious and sometimes fatal brain infection caused by the JC virus. Whether someone is at higher or lower risk depends mainly on three things: whether they carry JC virus antibodies (tested before and during treatment), how long they have been on the medicine, and whether they have had previous immune-suppressing treatment. People who are JC virus positive, especially with higher antibody levels and longer treatment, are at greater risk, and the treatment plan, including how often it is given, is tailored around this. Any new or worsening weakness, clumsiness, vision problems, difficulty speaking, confusion or personality change must be reported urgently. Infusion or injection reactions can also occur, so doses are given where people can be observed.
Who should not take it / use with caution
- People at high risk of PML, particularly some who are JC virus positive after longer treatment, may be advised against it.
- It is avoided in those with a seriously weakened immune system or a significant active infection.
- People with certain cancers or who cannot attend the required monitoring should not use it.
Monitoring
- JC virus antibody testing before and during treatment to assess PML risk.
- Regular clinical review and MRI scans to watch for early signs of PML.
- Liver-function tests and watching for infusion or injection reactions and infections.
Side effects
- Infusion or injection reactions, headache, tiredness and joint pain.
- A higher chance of infections, including urinary and chest infections.
- Rarely, the serious brain infection PML, and liver problems.
Key interactions
- It should not normally be combined with other immune-suppressing or other MS disease-modifying treatments, which raises infection risk.
- Live vaccines are generally avoided during treatment.
- Previous immune-suppressing treatment increases the PML risk and is taken into account.
Available as: A solution given as an infusion into a vein, or as an injection under the skin.
Answers
Natalizumab: frequently asked questions
What is the JC virus and why am I tested for it?
The JC virus is a common, usually harmless virus, but during this treatment it can rarely cause a serious brain infection (PML); testing for JC virus antibodies helps work out your risk.
What are the warning signs I should watch for?
Report new or worsening weakness, clumsiness, vision problems, difficulty speaking, confusion or personality changes straight away, as these can be early signs of PML.
Why is it so effective?
It stops immune cells crossing into the brain and spinal cord, which strongly reduces the inflammation that causes relapses.
Can I have it as an injection instead of a drip?
Yes; as well as a drip into a vein, it can be given as an injection under the skin, depending on what is suitable for you.
Can I stop it whenever I like?
Stopping should be planned with your specialist, as disease activity can return and the switch to another treatment needs to be managed carefully.
Authoritative sources
- BNF
- NICE CKS
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