Watson says it received generic Oxytrol challenge

Watson said it has received a paragraph IV certification letter, which means a rival has asked the Food and Drug Administration to approve a generic version of the drug. In such challenges, filers state that the patents protecting a branded drug are invalid, unenforceable, or that a generic version won't infringe on those patents.

Now that it has received the letter, Watson has 45 days to file a patent lawsuit against the company that submitted the application. Starting a lawsuit would automatically prevent the FDA from approving the generic for the next 30 months, or until a district court rules on the validity of the patent, whichever happens first.

The company did not say if it is preparing to file such a lawsuit.

The product is formally called the oxybutynin transdermal system. Watson is also developing an oxybutynin gel. The company said early in 2008 that it has completed late-stage testing of the product.

In aftermarket trading, Watson shares rose 13 cents to $29.10. The stock finished at $28.97.