Teva Pharmaceutical Industries Ltd said it settled a patent lawsuit with Pfizer Inc, allowing the Israeli drugmaker to launch a generic version of Pfizer's blockbuster painkiller Celebrex in December.

In March, a U.S. court invalidated a patent covering Celebrex, giving Pfizer's rivals a chance to sell cheaper versions. Pfizer had said it would appeal the ruling.

The drug, which is used to treat arthritis pain and inflammation, generated about $2.92 billion in sales in 2013, according to Pfizer's annual regulatory filing.

Teva, which is the world's largest generic drugmaker, said it believed it was the first to file for an approval of a generic of three dose strengths of Celebrex.

The U.S. Food and Drug Administration usually grants first-to-file drugmakers 180 days of marketing exclusivity.

Pfizer said on Thursday it would continue to defend the patent, which the U.S. Patent and Trademark Office granted in March, extending its marketing exclusivity until Dec. 2, 2015.

"Under certain conditions, the license will be royalty-bearing, through the remaining term of the patent (Dec. 2, 2015)," a Pfizer spokesman told Reuters in an emailed statement. "The remaining terms of the settlement are confidential."

The company sued several drugmakers, including Mylan Inc and Actavis Inc, which are also seeking U.S. regulatory approval to sell their generic versions of Celebrex.

Celebrex's basic chemical patent expires on May 30.

Teva's shares were up 1 percent at $50.43 in early trading on the New York Stock Exchange, while Pfizer's shares were little changed at $30.11.