* Merck to appeal decision on leading brain-cancer drug
* Teva generic awaiting U.S. approval
* Merck and Teva shares fractionally lower (Brings Merck response and detail of ruling higher; updates share movement)
By Ransdell Pierson
NEW YORK, Jan 26 (Reuters) - A federal court ruled on Tuesday that Merck & Co's (MRK.N) patent on Temodar, the world's top-selling brain cancer drug, is unenforceable, possibly clearing the way for Teva Pharmaceutical Industries Ltd (TEVA.TA) to sell a generic form of the medicine.
Temodar, which Merck acquired in its November purchase of Schering-Plough, has annual global sales of about $1 billion. It has annual U.S. sales of about $380 million, which would become prey to Teva's product.
Merck said it would appeal the decision and seek a stay to prevent Teva from launching its copycat product before the appeal runs its course.
"We are disappointed with the ruling and continue to believe the patent is valid and enforceable, and we will continue to defend our intellectual property," Merck spokesman Ron Rogers said.
District Judge Sue Robinson, of federal court in Delaware, ruled that the Merck patent was not enforceable, in part due to inequitable conduct.
Inequitable conduct refers to misstatements of fact by a party seeking a patent, or failure to candidly disclose relevant information to patent officials.
Teva's rival product has tentative marketing approval, but is awaiting final approval from the U.S. Food and Drug Administration. Once regulators clear it, the product is eligible for six months of marketing exclusivity before rival generics can go on the market, Teva said.
"Teva's generic already has tentative approval, so it's certainly possible we will see it approved and launched within the next 48 hours," said Leerink Swann analyst Seamus Fernandez.
"Once you have a district court decision, and you already have tentative approval, that releases the FDA" to take action, the analyst said.
Teva's less-costly medicine would likely batter sales of the Merck brand and depress Merck's earnings by 4 cents to 5 cents a share this year, and for several years to come, Fernandez said.
Sanford Bernstein analyst Aaron Gal said he expects Teva to launch its product in the second quarter and for it to have no competition from another generic until the third quarter.
Gal raised his 2010 Teva profit forecast by 6 cents a share, to $4.83, and lifted his 2011 forecast by 4 cents a share, to $4.89.
Merck contends the Temodar patent is valid through February 2014.
It is the second of Merck's products from last year's purchase of Schering-Plough to recently suffer a setback.
Merck said last Wednesday that its experimental HIV treatment vicriviroc proved ineffective in two late-stage studies involving patients who had previously been treated for the virus that causes AIDS.
Merck is continuing mid-stage studies of the drug among patients not previously treated for HIV.
Merck shares closed down 18 cents, or 0.5 percent, to $38.58 on the New York Stock Exchange. Teva TEVA.O shares on Nasdaq fell 9 cents to $56.99.
The case is Cancer Research Technology vs. Barr Laboratories Inc, U.S. District Court for the District of Delaware, No. 07-457. (Reporting by Ransdell Pierson and Bill Berkrot. Editing by Robert MacMillan, John Wallace and Tim Dobbyn)