NEW YORK (AP) — Biogen Idec Inc. has essentially received a 13-year patent extension on its biggest moneymaker, the multiple sclerosis drug Avonex, according to a Securities and Exchange Commission filing Tuesday. Key patents dealing with the production of Avonex are scheduled to expire in 2013. But in the regulatory filing, Biogen said it has received a patent for the drug's use in treating a viral condition, disease, cancer or tumor until September 2026. The so-called method of use patent also includes the use of Avonex as a multiple sclerosis drug. Sales of Avonex reached $591.2 million during the most recent quarter. The company would not say whether this new patent blocks any potential competitors seeking to bring a generic version of the drug to market between 2013 and 2026. The patent win comes as the debate over a pathway for copies of pricey biotechnology-based drugs continues to work its way through Congress. Currently, there is no system set up for drug developers to make generic equivalents of biotechnology-based treatments. Unlike their chemical-based counterparts, biotech drugs are made using living organisms, making the production process more complicated than just copying a formula. Biotech companies thus far have faced no generic competition and they are fighting to keep a strong position on the market. In proposal after proposal, the industry has backed bills seeking up to 14 years of market exclusivity for any new biotech-based drug, arguing the companies need that time to recoup costs that went into making the expensive treatments. Shorter periods, the industry argues, could cut incentives for companies to invest so much in developing the treatments. Meanwhile, the generic drug industry has been lobbying for much shorter periods of market exclusivity and would like any new system to mirror the current timeline for chemical compounds, currently about 5 years. Their argument has centered on cost-savings for consumers, though the savings wouldn't be as large as that seen with copies of chemical-based drugs. Biotech-based cancer treatments such as Genentech Inc.'s Avastin can cost up to $50,000 per year.