Natalizumab, sold under the brand name Tysabri, is a prescription medication approved by the Food and Drug Administration (FDA) for treating adults with multiple sclerosis (MS). Natalizumab is not a cure for MS, but it can decrease the number of flare-ups and help delay or prevent disability. Natalizumab is a monotherapy, which means that cannot be combined with any other MS drug. Due to the risk of serious side effects, it is usually only recommended for patients who have not responded well to other MS drugs. Natalizumab is not recommended for people who have weakened immune systems or who have ever had a certain virus called the John Cunningham virus. Natalizumab is not appropriate for pregnant women, women who might become pregnant, or women who are breastfeeding.
Natalizumab is an immunomodulator, or in other words, a drug that modulates the immune system. It is a genetically engineered antibody, or type of protein used by the immune system to identify and neutralize substances. Natalizumab is believed to work by attaching to immune cells called lymphocytes (a type of white blood cell) and preventing them from crossing the blood-brain barrier. By blocking the lymphocytes’ access to the central nervous system, Natalizumab prevents them from attacking the brain and nerves and causing the lesions that result in MS symptoms.
How do I take it?
In order to take Natalizumab, you must be accepted to a restricted program called the TOUCH Prescribing Program. TOUCH, which stands for Tysabri Outreach: Unified Commitment to Health, is sponsored by the drug’s manufacturer. You will have to answer many questions about your health history that relate to your immune system, and you may undergo a blood test for John Cunningham virus. You may also receive a magnetic resonance imaging (MRI) scan to check for any sign of brain infection. If you are accepted, you will go to a medical facility to receive Natalizumab via intravenous infusion once every 28 days.
Always follow your doctor’s instructions exactly when taking Natalizumab.
The FDA approved Natalizumab (Tysabri) for MS in 2004 based on two clinical studies. In the first two-year study, which involved 942 people, 67 percent of those taking Natalizumab did not have a relapse, while 41 percent of those on the placebo relapsed. Of those on Natalizumab, 17 percent saw a sustained increase in disability, compared with 29 percent of those on the placebo.
The second trial involved 1,171 participants over two years. In this study, 54 percent of those taking Natalizumab remained relapse-free, while 32 percent of those on the placebo experienced relapses. Of those on the drug, 23 percent showed a sustained increase in disability, while 29 percent of those taking the placebo suffered an increase in disability.
The most serious side effects of Natalizumab are liver damage and a brain infection called progressive multifocal leukoencephalopathy (PML), both of which are rare. People taking Natalizumab may also have an elevated risk of developing leukemia and other cancers.
PML is caused by the John Cunningham virus, which is ordinarily harmless except in people whose immune systems are seriously compromised. PML can cause major disability or death. People who don’t have the virus in their systems are not at high risk for contracting PML when taking Natalizumab. Other risk factors include having previously taken another MS drug that suppresses the immune system and remaining on Natalizumab for more than two years.
Signs of liver damage can include dark brown urine, yellow skin and extreme tiredness. Call your doctor if you experience any of these.
More common side effects are fatigue, stomach pain, nausea, vomiting, sore throat, headache, skin irritation at the injection site, and general skin problems such as bleeding, crusting or blistering. Since Natalizumab lowers your body’s immune system defenses, it can make it easier to contract urinary tract, lung and other infections.
Seek medical help immediately if you experience symptoms of an allergic reaction such as trouble breathing, severe dizziness, a rash, or itching or swelling of the face, tongue and throat.