Natalizumab
This medication comes under the name of Tysabri, and it blocks the movement of the immune cells that potentially damage the brain and spinal cord. This medication is the first choice as a treatment for the people having severe symptoms of multiple sclerosis. While it is the second choice of treatment for the patients having less severe symptoms, unfortunately, this medication increases the risk of viral infections in the brain, particularly causing progressive multifocal leukoencephalopathy(PML) in patients who have antibodies of the causative agents of PMLJC virus.