FDA approved Elan/Biogen Idec's multiple sclerosis monoclonal antibody Tysabri (natalizumab),formerly Antegren , onNov. 23 based on one-year data from two Phase III trials.

The monotherapy trial, AFFIRM, is a randomized, multicenter, placebo-controlled, double-blind study of 942 patients conducted in 99 sites worldwide.

After one year of treatment, 300 mg IV administered once a month to 627 patients reduced the rate of relapse by the statistically significant amount of 66% compared to placebo administered to 315 patients.

The add-on study, SENTINEL, is a randomized, multicenter, placebo-controlled, double-blind study of 1,171 Avonex patients conducted in 123 sites worldwide.

Biogen Idec's Avonex (interferon beta-1a) is the current market leader in MS therapies (¹ Also see "Elan/Biogen Idec Antegren Will Set Premium Price In Multiple Sclerosis" - Pink Sheet, 13 May, 2004.).

The addition of Tysabri to Avonex resulted in a 54% reduction in the rate of clinical relapse over the effect of Avonex alone. The annualized relapse rate was 0.36 for patients receiving Tysabri when added to Avonex versus 0.78 with Avonex plus placebo.

As a condition of approval, the companies will collect two-year data from the trials. Results are anticipated "beginning in the first half of 2005."

Biogen Idec said it expects to first market the therapy to patients who have failed on existing therapies.

In addition to the company's Avonex, other therapies available for MS include Serono/Pfizer's Rebif (interferon beta-1a), Berlex' Betaseron (interferon beta-1b) and Teva's Copaxone (glatiramer) (² Also see "Rebif Ready For Antegren Following MS Market Share Gains, Serono Says" - Pink Sheet, 26 October, 2004.).

The Tysabri BLA was submitted in May. The product received accelerated approval "because it appears to provide substantial benefit for patients with a serious disease," FDA said.

- Andrew Shelton

Elan/Biogen Idec's Tysabri, Formerly Antegren, Approved For MS Based On One-Year Data

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