Watson Pharmaceuticals Inc. is suing Barr Pharmaceuticals Inc. to prevent them from selling a generic version of the Oxytrol overactive bladder patch, the Associated Press reported. Watson filed a lawsuit against Barr in the U.S. District Court of Delaware, saying Barr''s planned generic version of Oxytrol violates Watson''s patent on the drug. Earlier this month, Watson received a letter from the Food and Drug Administration telling it Barr was challenging the patent on Oxytrol. That letter, called a paragraph IV certification, gives drug makers 45 days to file a lawsuit defending its patent. Now that Watson has filed the suit, the FDA will not approve any generic versions for 30 months unless a court invalidates the patent. Oxytrol is formally called the oxybutynin transdermal system. Watson is also developing a gel version of the product.