Natalizumab

Natalizumab, sold under the brand name Tysabri among others, is a medication used to treat multiple sclerosis and Crohn's disease. It is a humanized monoclonal antibody against the cell adhesion molecule α4-integrin. It is given by intravenous infusion. The drug is believed to work by reducing the ability of inflammatory immune cells to attach to and pass through the cell layers lining the intestines and blood–brain barrier.

Natalizumab, is a monoclonal antibody which targets a protein called α4β1 integrin on white blood cells involved in inflammation. By attaching to integrin, natalizumab is thought to stop white blood cells from entering the brain and spinal cord tissue, thereby reducing inflammation and the resulting nerve damage.

The most common side effects are urinary tract infection, nasopharyngitis (inflammation of the nose and throat), headache, dizziness, nausea, joint pain and tiredness.

Natalizumab was approved for medical use in the United States in 2004. It was subsequently withdrawn from the market by its manufacturer after it was linked with three cases of the rare neurological condition progressive multifocal leukoencephalopathy (PML) when administered in combination with interferon beta-1a, another immunosuppressive drug often used in the treatment of multiple sclerosis. After a review of safety information and no further deaths, the drug was returned to the US market in 2006 under a special prescription program. As of June 2009, ten cases of PML were known. However, twenty-four cases of PML had been reported since its reintroduction by October 2009, showing a sharp rise in the number of fatalities and prompting a review of the chemical for human use by the European Medicines Agency. By 2010, 31 cases of PML were attributed to natalizumab while by 2018 this had risen to 757 cases. The US Food and Drug Administration (FDA) did not withdraw the drug from the market as benefits outweigh the risks. In the European Union, it has been approved only for multiple sclerosis and only by itself as the initial cases of PML, and later the fatalities, were said by the manufacturers to be linked to the use of previous medicines by the person.