Teva Pharmaceuticals (TASE, Nasdaq: TEVA) shares dropped 1.3% on Wall Street last Friday, and that's after the bell. The share had actually closed with a 3.9% gain, but then it revealed a setback in court.

A New York court ruled that a patent registered by the Japanese drug company Eisai for Aciphex, valid through 2013, is enforceable. Petah Tikva-based Teva says it will appeal, Bloomberg reports.

Aciphex's generic name is rabeprazole sodium. It is a proton-pump inhibitor that suppresses the secretion of stomach acids.

The United States District Court for the Southern District of New York was the latest ruling on a flurry of lawsuits that began in November 2003, when Eisai filed infringement actions against Teva and Dr. Reddy's Laboratories in respect to their abbreviated new drug applications for Aciphex.

Teva had received United States Food and Drug Administration approval for its generic version of the drug in February 2007. It's a big one: Eisai sold $1.3 billion of the stuff in 2006. Teva expected to receive exclusive marketing rights, or share them with the Indian pharma Dr Reddy's. HSBC calculated that an exclusive Teva launch of generic Aciphex could increase the Israeli company's sales by $115-174 million.

Teva and Dr. Reddy's argued that Eisai had withheld information from the U.S. Patent and Trademark Office to win its patents. Even if true, shrugged the judge, the error was not grave enough to warrant the extreme sanction of voiding a patent.

In October 2006, the New York court granted partial summary judgment to Eisai, upholding the validity of the Aciphex "composition of matter" patent. Now Judge Lynch has also determined that Eisai's patent is enforceable

"All issues in the case have been resolved, and final judgment will be entered in favor of Eisai," the Japanese company stated, somewhat hopefully.