Tysabri Two-Year Monotherapy Data Support Positive One-Year Efficacy Findings

Two-year data from the AFFIRM Phase III monotherapy trial showed that treatment with Tysabri led to a significant reduction in disability progression, the rate of clinical relapses and brain lesions in patients with relapsing forms of multiple sclerosis (MS).

AFFIRM met all primary and secondary endpoints, including disability progression and relapse rate. Tysabri (natalizumab) treatment was also associated with a low level of immunogenicity. Tysabri treatment led to a 42 percent reduction in the risk of disability progression compared to placebo. Tysabri also reduced the rate of clinical relapses by 67 percent compared to placebo, which was sustained and consistent with the previously reported one-year results.

On Feb. 28, Biogen Idec and Elan announced that they voluntarily suspended Tysabri from the U.S. market and all ongoing clinical trials. This decision was based on reports of progressive multifocal leukoencephalopathy (PML), a rare and frequently fatal, demyelinating disease of the central nervous system. The companies' comprehensive safety evaluation concerning Tysabri and any possible link to PML is ongoing. The results of this safety evaluation will be discussed with regulatory agencies to determine possible re-initiation of dosing in clinical trials and future commercial availability.