By Brendan Pierson WASHINGTON (Reuters) - The U.S. Supreme Court on Monday declined to hear a case over whether companies that make copycat versions of biologic drugs must wait six months after winning federal approval before bringing them to the market. The justices opted not to take up Apotex Inc's appeal of a July federal appeals court ruling that could delay the Canadian generic drug maker's launch of so-called biosimilar versions of California-based Amgen Inc's Neulasta, used to fight infection in cancer patients. Approved by the U.S. Food and Drug Administration in 2002, Neulasta is one of Amgen's top-selling products, accounting for $4.7 billion of its nearly $21 billion in sales last year. Biologic drugs like Neulasta are made using living cells. Unlike traditional drugs, biologic drugs cannot be copied exactly to make generic versions. A 2010 federal law, the Biologics Price Competition and Innovation Act, allows companies to seek approval to sell near-copies called biosimilars. Novartis AG's Sandoz unit also has applied to make biosimilar versions of Neulasta and of Amgen's Neupogen, an older and less popular drug that works similarly but must be given more often. Neither application has yet been approved. The biosimilars law gives the maker of a biologic drug 12 years of exclusive rights before the U.S. Food and Drug Administration can approve a biosimilar. It also states that a biosimilar maker must give the original biologic drug maker 180 days' notice before launching its copycat version. Amgen has argued that the 180-day period cannot begin until the biosimilar is approved. The U.S. Court of Appeals for the Federal Circuit agreed in July, barring Apotex from launching its biosimilar until 180 days after approval. In its petition asking the Supreme Court to review that decision, Apotex said the Federal Circuit wrongly added an extra six months to the law's 12-year exclusivity period. It also argued that it should be exempt from the 180-day notice requirement entirely, because it voluntarily took part in a patent dispute resolution process under the biosimilars law. A federal judge in Florida rejected patent infringement claims by Amgen over Apotex's biosimilars in September. The Obama administration's solicitor general has weighed in on a Supreme Court petition from Sandoz unit in its similar dispute with Amgen, coming down against the 180-day wait.