See the DrugPatentWatch profile for Tysabri
What side effects are linked to Tysabri (natalizumab)?
Tysabri (natalizumab) can cause side effects that range from mild reactions to serious complications. The biggest safety concern is progressive multifocal leukoencephalopathy (PML), a rare but potentially fatal brain infection. [1]
Other side effects reported with Tysabri include infusion-related reactions and general immune-related effects. [1]
What are the most serious risks, including PML?
PML is the key serious risk associated with Tysabri. It can cause worsening neurological symptoms (for example, weakness, vision problems, trouble speaking, or changes in thinking/behavior). If PML is suspected, treatment is stopped and urgent medical evaluation is needed. [1]
Risk of PML is higher in some situations, such as longer use, prior exposure to certain immune-weakening therapies, and presence of specific antibodies related to JC virus. Clinicians use these factors to decide whether Tysabri is appropriate and how to monitor patients. [2]
What side effects happen during or soon after infusions?
Some people experience infusion-related reactions. These can include symptoms such as fever, chills, flushing, rash, nausea, or trouble breathing during or shortly after an infusion. If symptoms occur during an infusion, the infusion may be slowed or stopped, and medical care is provided. [1]
What should patients watch for day to day?
Patients are generally advised to watch for symptoms that could signal infection, allergic reactions, or neurologic changes. Because PML can develop over time, new or worsening neurological symptoms should be treated as urgent and prompt medical assessment is recommended. [1]
Who is most at risk for severe side effects?
Your PML risk depends on individual risk factors clinicians consider when prescribing and monitoring Tysabri, including:
- How long you’ve been on Tysabri
- Whether you previously used other immune-suppressing therapies
- Whether you test positive for antibodies related to JC virus [2]
How can Tysabri side effects be reduced or monitored?
Clinicians reduce risk mainly through:
- Careful selection of candidates for treatment
- Ongoing monitoring, including JC virus testing and reassessing risk over time [2]
- Stopping Tysabri if PML is suspected or confirmed [1]
When to seek emergency care
Get urgent medical attention if you develop symptoms that could suggest a serious reaction or infection, especially new or worsening neurological symptoms that could fit PML (such as weakness on one side, vision changes, difficulty speaking, severe confusion, or major behavior/thinking changes). [1]
What are common vs. rare side effects?
Milder side effects can occur, but serious effects like PML are rare. The risk profile depends on personal factors (especially PML-related risk factors), so the most relevant “common” experience varies by patient. PML remains the most critical rare serious risk that requires strong monitoring. [1][2]
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Sources
[1] https://www.accessdata.fda.gov/scripts/cder/daf/index.cfm?event=overview.process&ApplNo=761063
[2] https://www.ncbi.nlm.nih.gov/books/NBK560473/