Questions and Answers on Natalizumab
1. What is natalizumab?
Natalizumab is a monoclonal antibody that binds to a protein called alpha-4-integrin. Integrins are found primarily on the surface of white blood cells, and play a role in immune system activity.
2. What are monoclonal antibodies?
Antibodies are naturally occurring proteins produced by the immune system in response to foreign substances. Once produced by the body, they recognize and bind to specific proteins (antigens) on bacteria, viruses, and toxins, to help the body fight disease.
Monoclonal antibodies, such as natalizumab, are produced in cell culture systems. They can be designed to bind to receptors on the body’s normal cells. By recognizing and attaching to these receptors, monoclonal antibodies can interfere with (or alter) normal or abnormal cellular responses. In this way, monoclonal antibodies may be useful in the treatment of certain diseases.
3. What is natalizumab used to treat?
Natalizumab is approved to treat patients with relapsing forms of multiple sclerosis to reduce the frequency of exacerbations. It was approved based on results achieved after approximately one year of treatment in ongoing controlled trials. These trials will continue for another year. At this time, the safety and efficacy of natalizumab beyond one year are not known.
Safety and efficacy in patients with chronic progressive multiple sclerosis have not been established.
4. What is multiple sclerosis?
Multiple sclerosis (MS) is a disease in which the immune system attacks the person's brain and spinal cord. The disease causes a wide range of symptoms including fatigue, difficulty walking, numbness, and vision problems.
5. What is relapsing MS?
This type of MS is characterized by relapses (also known as exacerbations or attacks) during which new symptoms can appear and old ones resurface or worsen. The person fully or partially recovers from the deficits acquired during the relapse. Relapses are followed by periods of remission, during which no new symptoms occur.
6. How does natalizumab work?
White blood cells are thought to play a major role in causing the damage to the nervous system in MS. Natalizumab binds to white blood cells and interferes with their movement from the bloodstream into the brain and spinal cord
7. Is natalizumab a cure for MS?
No, natalizumab will not cure MS. In a study in which patients were randomly assigned to treatment with either natalizumab or placebo (an inactive substance), natalizumab reduced the average yearly relapse rate from 0.74 relapses per patient in the placebo group, to 0.25 relapses per patient in the natalizumab treated group. This is a relative reduction of 66%.
8. What is accelerated approval?
Accelerated approval is a program the FDA developed to make new drug products available for serious or life threatening diseases when they appeared to provide a benefit over available therapy (which could also mean there was no existing effective treatment). Under this program, natalizumab is being approved on the basis of early clinical study evidence (such as data from only one year of study) suggesting that the drug is reasonably likely to have a valuable effect on symptoms.
Several other products are already available for the treatment of MS, including Betaseron, Avonex, Rebif, Copaxone, and Novantrone. One of the clinical studies with natalizumab was performed in patients already being treated with Avonex. The addition of natalizumab resulted in a further reduction in the occurrence of relapses, beyond the benefit that those patients had already received from Avonex.
The approval is granted on the condition that the manufacturer must continue testing to demonstrate that the drug indeed provides therapeutic benefit to the patient. If it does not, the FDA can withdraw the product from the market more easily than usual.
9. How is natalizumab given?
Natalizumab is given by intravenous (in to a vein) infusion every four weeks.
10. What are the possible side effects of natalizumab?
The most frequently reported serious side effects with natalizumab are infections, severe or life threatening allergic reactions, depression (including thoughts of suicide) and gallbladder problems. In the trials, these serious side effects occurred at a rate of 0.8% for serious depression and gallbladder problems, at a rate of 2.1% for serious infections.
Common side effects include:
- Joint pain
- Menstrual disorders
A complete list of side effects may be found in the product labeling.
11. Where can I find more information on natalizumab and MS?
Go to FDA's natalizumab web page at: Natalizumab (marketed as Tysabri) Information
Go to the National Library of Medicine web page at: