Amgen Inc. in Thousand Oaks has filed a lawsuit against drugmaker Intas Pharmaceuticals Inc. and its subsidiary Accord Healthcare Inc. over its plans to manufacture a generic of Amgen’s medication Sensipar.

In a document filed June 28 in the U.S. District Court of Delaware, Amgen alleged that Durham, N.C.-based Accord had filed an application with the U.S. Food and Drug Administration to market a generic version of Sensipar, which is used to lower calcium levels in the blood in patients who have parathyroid cancer.

Earlier this year, Amgen’s bid to overturn an FDA ruling that the company could not extend its patent for the use of Sensipar in pediatric patients for an extra six months was overturned by a U.S. District Court judge. The patent for the use of the medication in pediatric patients expired on March 8, but the company has a formulation patent for the drug that expires in 2026.

Domestic sales of Senispar were $1.37 billion in 2017, according to Securities and Exchange Committee filings.

Amgen declined to comment on the lawsuit on account of pending litigation. Accord did not respond to a request for comment by press time.

Amgen employs around 5,500 workers in Thousand Oaks and approximately 20,800 company-wide.

Shares of Amgen (AMGN) rose $1.65, or about 1 percent, on Thursday to close at $187.36 on the Nasdaq.