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.