Eliquis. (Courtesy photo)

Bristol-Myers Squibb Co. and Pfizer Inc. on Monday filed a slew of patent infringement suits in Delaware to protect their patents for the successful drug Eliquis and halt the development of generic versions of the profitable blood thinner.

The companies, which jointly develop the drug, targeted at least 13 generic drugmakers in cases filed in the U.S. District Court for the District of Delaware, bringing the total tally to no less than 16. The flurry of litigation kicked off last week with a case filed against Mylan Inc. The new cases were filed Monday and entered to an online docket tracking system Tuesday morning.

All of the defendants had planned to develop versions of Eliquis, which is used to decrease the chance of stroke in certain patients. The drug brought in around $3.3 billion in revenue last year for Bristol-Myers Squibb, and Pfizer made approximately $1.6 billion in sales off Eliquis in 2016.

Bristol-Myers Squibb and Pfizer also got a big boost in March, when they announced study results showing Eliquis reduced the risk of stroke by 60 percent, compared to competing blood-thinning medication warfarin. The companies also said analysis showed their drug reduced major bleeding by 49 percent, compared to warfarin.

A number of competitors had filed abbreviated new drug applications with the U.S. Food and Drug Administration to make and sell 2.5 mg and 5 mg tablets of apixaban, the generic name for Eliquis. Like Eliquis, the generics would be administered orally to treat patients with deep vein thrombosis and pulmonary embolism.

In the Delaware litigation, Bristol-Myers Squibb and Pfizer are seeking declarations that two patents for Eliquis are valid and enforceable, and allege the planned generics would infringe on one owned by Bristol-Myers Squibb and another owned by both companies.

“If Accord’s marketing and sale of the Accord ANDA product prior to expiration of the ’945 patent and all other relevant exclusivities are not enjoined, plaintiffs will suffer substantial and irreparable harm for which there is no remedy at law,” attorneys for the companies wrote in a complaint against North Carolina-based Accord Healthcare Inc.

The plaintiffs were referencing a jointly owned patent for “apixaban formulations,” issued by the U.S. Patent and Trademark Office in May 2016. Bristol-Myers Squibb also individually owns the so-called ’208 patent, issued in 2005.

The suits assert two counts of infringement and seek both monetary and injunctive relief. They have not yet been assigned to a judge.

Joseph J. Farnan Jr., Brian E. Farnan and Michael J. Farnan of Farnan LLP are listed as attorneys for Bristol-Myers Squibb and Pfizer.

Bristol-Myers Squibb and Pfizer are themselves facing allegations that they hid risks associated with Eliquis. Those cases have been consolidated into multidistrict litigation in the U.S. District Court for the Southern District of New York.

Spokespeople for the companies were not immediately available to comment on the most recent litigation in Delaware.