NEW YORK (AP) — Sepracor Inc. on Friday took a step toward a potential challenge of patents supporting Pristiq, an antidepressant marketed by Wyeth. Sepracor says it discovered the drug first and filed an application for a patent in April 1999, almost two years before Wyeth made its first filing in February 2001. The Board of Patent Appeals and Interferences of the U.S. Patent and Trademark Office plans to hear arguments from the two companies on Jan. 6, 2010. Sepracor says the patent interference is between two patents awarded to Wyeth, and three given to Sepracor. The board will rule on who invented the drug first and who will hold the patents. If the board rules in favor of Sepracor, it could be awarded a patent on Pristiq and potentially sue Wyeth for patent infringement. Doug Petkus, a spokesman for Wyeth, said his employer would win the challenge. "Wyeth will prove during the upcoming proceedings before the patent office that we invented desvenlafaxine and that Sepracor's position is without merit," he said. Marlborough, Mass.-based Sepracor calls the chemical O-desmethylvenlafaxine succinate, and Wyeth, of Madison, N.J., uses the name desvenlafaxine. Wyeth began selling Pristiq in February 2008, and some Wall Street analysts believe it could be a replacement for the multi-billion-selling depression treatment Effexor. Worldwide sales totaled $66.5 million last year. Wyeth agreed to sell itself to larger rival Pfizer Inc. in January, in a deal valued at $68 billion.