Many drugs which offer promising cures when first introduced later prove to be ineffective or even dangerous. One that falls in the dangerous category is Tysabri, manufactured by Biogen, Inc. Tysarbi is a prescription medicine approved for patients with relapsing forms of MS. It has been shown to slow the worsening of disability that is common in patients with MS and decrease the number of flare-ups or relapses of the disease.
However, Biogen recently reported the ninth confirmed case of progressive multifocal leukoencphalopathy (PML)
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