Watson Pharmaceuticals has announced that it is challenging drug giant Pfizer's patent protecting its antidepressant Pristiq, in the hope of being the first to get a generic version on the market.

The company revealed that its subsidiary Watson Laboratories has filed an application with the US Food and Drug Administration to seeking approval to market desvenlafaxine succinate extended-release tablets 50mg and 100mg for the treatment of major depressive disorder in adults.

The group said it believes it is the first to to file an abbreviated New Drug Application for a generic version of Pristiq and, if successful, could therefore be entitled to 180 days of generic market exclusivity.

However, Pfizer and its partners have filed a suit in the US District Court for the District of Delaware in an attempt to prevent Watson from selling its copycat drug before Pristiq's patent has expired.  

Consequently, the FDA will delay its decision until August 29, 2015, unless the court case is resolved sooner, the firm said.

Pristiq reportedly pulls in annual sales of around $560 million.