Natalizumab (Tysabri) slows progression of disability in patients with relapsing forms of MS- two year data from AFFIRM trial: Biogen Idec and the Elan Corporation have announced that the Phase III natalizumab (Tysabri™) AFFIRM monotherapy trial has achieved the two-year primary endpoint of slowing the progression of disability in patients with relapsing forms of MS.

Natalizumab led to a 42% reduction in the risk of disability progression compared to placebo. These data also demonstrated a 67% reduction in the rate of clinical relapses over two years, which was consistent with the previously reported one-year results. Other data from AFFIRM at two years, including MRI measures and immunogenicity, were similar to previously reported results.

The adverse event profile at two years was also consistent with previously reported results. The incidence of infections in natalizumab-treated and placebo-treated patients was similar. Serious infections occurred in 3.2% and 2.6% of patients, respectively. Natalizumab has also been associated with hypersensitivity reactions, including serious systemic reactions that occurred at an incidence of less than 1% of patients.