Biogen Idec Inc. (NASDAQ:BIIB), the fourth- largest U.S. biotechnology company by market value, won a U.S. patent that may guard its experimental multiple sclerosis pill from generic competition for eight more years than anticipated.

The company’s patent 8,399,514, which expires in 2028, was issued on an application filed in February 2012 by Weston, Massachusetts-based Biogen, according to the U.S. Patent and Trademark Office’s website. The Food and Drug Administration is expected to decide whether to approve the medicine, Tecfidera, by the end of the month.

The drug had been protected by three patents that expire from October 2019 to May 2020, according to Eric Schmidt, a New York-based analyst with Cowen & Co. who estimates Tecfidera could generate $3.2 billion in annual sales in 2017. The drug was tested in doses given twice a day and three times a day, and the patent today covers administration twice daily.

“They have a novel discovery here in that they were first to observe that the lower dose of the drug, maybe somewhat surprisingly, was as active as the high dose,” Schmidt said in a telephone interview. “The burden of proof will be on anyone else to show this patent isn’t valid.”

Biogen already sells the MS treatments Avonex, given by injection, and Tysabri, administered intravenously. Biogen makes both drugs at its drugs manufacturing plant in Research Triangle Park. Tecfidera, formerly known as BG-12, would be Biogen’s first pill for MS, a disease that affects more than 2.1 million people globally, according to the National Multiple Sclerosis Society.

“The patent for this dosing regimen is recognition of the remarkable innovation Tecfidera represents for the MS community,” Biogen Chief Executive Officer George Scangos said in a statement. “The tremendous research investment required to study and validate the patented dosing regimen is an example of innovation that leads to meaningful benefits to patients.”