Drug That Slows Progression of Multiple Sclerosis OKd

The first drug to slow the progression of multiple sclerosis has been approved by the Food and Drug Administration, but the maker of a competing medicine plans to ask a court to block its introduction.

The FDA announced Friday that it will permit marketing of Avonex for the treatment of relapsing forms of multiple sclerosis.

Avonex, made by Biogen Inc. in Cambridge, Mass., is the second approved MS drug that is based on interferon, one of the proteins produced by the immune system.

The other drug, Betaseron, is slightly different from Avonex. Betaseron, which has been shown to reduce the rate of flare-ups of the disease but does not slow its progression, was licensed in July 1993.

Betaseron’s marketer, Berlex Laboratories Inc., filed a lawsuit last month in U.S. District Court in Washington, attempting to stop distribution of Avonex, but a judge rejected the request, saying it was premature prior to Avonex’s approval. Berlex executive Jeffrey Latts said Friday the company will now seek an injunction to stop sales of Avonex until the suit is resolved.

Berlex contends that Avonex is so close to Betaseron that its approval would violate a seven-year period of exclusive marketing rights granted under the federal Orphan Drug Act.