Tysabri® (natalizumab)

Parent companies: Biogen Idec and Elan Pharmaceuticals, Inc.

Administered via intravenous infusions every four weeks
Humanized monoclonal antibody approved for relapsing forms of MS.

Blocks activated immune-system cells from crossing blood-brain barrier (BBB) into central nervous system (CNS).

FDA granted approval based on 66-percent reduction in relapses compared to placebo (AFFIRM trial) and 54-percent reduction in relapses for those taking Tysabri plus Avonex, versus Avonex plus placebo (in Avonex-treated patients with continued disease activity).

Temporarily suspended when two patients taking both Tysabri and Avonex developed Progressive Multifocal Leukoencephalopathy (PML), an often-fatal viral disease occurring in immuno-suppressed patients.

Since its re-release, 10 months into safety studies (TOUCH program in United States), no new cases of PML found; participants continue to be monitored.

Three-year data show continued effectiveness (reduction in relapses, favorable MRI data, and a reduction in progression of disability).