LINDA A. JOHNSON AP Business Writer TRENTON, N.J. (AP) — The patent for Merck & Co.’s blockbuster allergy and asthma drug is valid, a federal judge ruled Wednesday, handing the drugmaker a crucial victory in its 2 1/2-year legal battle to block a rival from selling a cheaper generic version. U.S. District Judge Garrett E. Brown Jr. upheld the patent for Singulair, which as Merck’s top-selling drug provides about one-sixth of its annual revenue. Brown also issued an injunction that prevents Israel’s Teva Pharmaceuticals from selling generic Singulair, a long-term drug to prevent asthma and allergy flare-ups, in the U.S. until the patent expires in August 2012. Bruce Kuhlik, general counsel for Whitehouse Station, N.J.-based Merck, said in a statement that the ruling was appropriate and that the company vigorously defends its patent rights. Singulair brought Merck sales of $4.3 billion last year, and slightly higher sales are expected this year. “We are currently reviewing the court’s decision to determine our next course of action,” Teva spokeswoman Denise Bradley said. She said she could not discuss its options. Teva Pharmaceuticals USA, a subsidiary of Teva Pharmaceutical Industries Ltd., had sought approval from the U.S. Food and Drug Administration in February 2007 to sell generic Singulair pills in three doses. Merck filed a lawsuit in April 2007 claiming that Teva, the world’s top generic drugmaker, would be infringing on its patent for Singulair, known chemically as montelukast. Brown, seated in Trenton, presided over a nonjury trial from Feb. 23 to 26. His ruling Wednesday came just three days before Saturday’s expiration of an automatic 30-month stay, preventing Teva from manufacturing or selling generic Singulair, that was triggered by the legal battle. Teva had argued that Merck’s basic patent for Singulair was invalid because previously available scientific information made the chemical structure of the drug “obvious.” Teva also claimed Merck allegedly committed “inequitable conduct” by concealing that in its application to the U.S. Patent and Trademark Office in the early 1990s. The Israeli company specifically cited a 1989 publication in a scientific journal, complete with a molecular model, by a scientist named Robert Young at a Merck subsidiary in Canada. In his 102-page ruling, Brown concluded Merck presented sufficient evidence that the design of montelukast was not obvious because at least eight other companies had tried to develop drugs that work by the same method, by blocking leukotrienes. Virtually all of those other experimental compounds failed to make it through testing, Brown noted. Leukotrienes are airway-constricting substances produced by the body in response to an asthma attack or allergy flare-up, usually along with histamines, in an overreaction by the immune system. Brown also cited evidence that “Teva has sought to copy Singulair,” based on the information it submitted to the FDA in its request to sell generic versions. The judge wrote that this “also weighs against the conclusion” that the patent information is obvious. Merck spokesman Ron Rogers said Teva had filed a second application with the FDA to sell a form of Singulair in granules, for mixing into favorite foods for young children, late in 2008. Merck filed a lawsuit to block that attempt in January. “Both parties agreed that today’s decision would determine the outcome of the second lawsuit,” so that case also has ended, Rogers said. Teva is the No. 12 pharmaceutical company based on global revenue. Merck is the world’s No. 8 drugmaker, but will leapfrog to No. 2 when it closes its $41.1 billion acquisition of New Jersey neighbor Schering-Plough Corp. in the fourth quarter. Singulair has been on the market since 1998.