Pharmaceutical company Pfizer Inc. announced it will appeal a ruling that invalidated a patent extension related to its osteoarthritis drug Celebrex. This ruling could influence Pfizer's current lawsuit against generic drug companies that plan to create a generic version of the medicine to begin selling at the end of May, when Pfizer's original patent expires.

The U.S. District Court in Eastern Virginia invalidated a patent reiusse for celecoxib, the active ingredient in Celebrex. This decision took place just ahead of a trial scheduled to begin March 19 for Pfizer's infringement case against several generic drug companies.

"Pfizer disagrees with the ruling and will pursue all available remedies, including an immediate appeal of the court's decision," the company said in a statement.

The expiration of Pfizer's patent for celecoxib will expose the company to possible losses as cheaper generic versions become available. In the fourth quarter of 2013 alone, Celebrex generated $800 million in sales, according to IndustryWeek. Many generic drug companies intend to release such a version, including U.S. companies Mylan Pharmaceuticals and Watson Laboratories, Canadian firm Apotex, India's Lupin and Israeli company Teva, which is the world's largest manufacturer of generic drugs.