Pfizer Inc. on Monday accused Florida-based generic drugmaker Breckenridge Pharmaceutical Inc. of infringing four patents for Xeljanz, as the company continues its campaign to protect the rheumatoid arthritis drug from generic competition.

The suit, filed in the U.S. District Court for the District of Delaware, was prompted by Breckenridge’s abbreviated new drug application, filed last month with the U.S. Food and Drug Administration, to develop 5 mg generic tablets containing tofacitinib citrate, the same active ingredient used in Xeljanz.

Pfizer said Breckenridge alerted it to the ANDA filing in a letter Sept. 22, saying that the patents were invalid and unenforceable and thus would not be infringed by the sale of the planned Xeljanz copies.

In the complaint, Pfizer asked the court to delay FDA approval of Breckenridge’s generics until at least 2025, when the last of the four patents is set to expire. The disputed patents were issued between 2005 and 2010, Pfizer said, though two other patents that Pfizer holds for Xeljanz were not affected.

Pfizer’s lawsuit comes as the company is trying to hold off generic competitors from muscling in on what has been a profitable segment of the U.S. and international markets.

Pfizer has reported increasing revenues for Xeljanz in each of the first three quarters of 2017, and said that it sees the drug as one of its key growth drivers.

In Pfizer’s most recent quarterly report, filed Tuesday with the U.S. Securities and Exchange Commission, Pfizer said U.S. sales of Xeljanz were up 44 percent to $290 million in the third quarter, compared with $202 million during the same three-month period a year ago.

Earlier this year, Pfizer sued Micro Labs USA Inc., Zydus Pharmaceuticals Inc. and Prinston Pharmaceutical Inc. for infringement after the drugmakers applied to bring their own 5 mg generic versions of Xeljanz to market.

In February, the company also sued to halt Sun Pharmaceuticals Inc. over an ANDA seeking approval to develop a generic version of Pfizer’s 11 mg extended-release tablets.

A spokeswoman for Pfizer did not respond Tuesday to a call seeking comment on the litigation. A call to Breckenridge was not returned.

Pfizer is represented by Jack B. Blumenfeld and Maryellen Noreika of Morris, Nichols, Arsht & Tunnell. An online docket-tracking service did not provide information regarding Breckenridge’s legal representation.

The case is captioned Pfizer v. Breckenridge Pharmaceutical.