The Supreme Court Monday rejected a generic-drug maker's appeal challenging a patent for a blockbuster blood-thinning drug developed by Sanofi-Aventis SA and co-marketed by Bristol-Myers Squibb Co.

The dispute arose after the Canadian generic-drug maker Apotex Corp. applied to market a generic version of the anti-blood-clotting drug Plavix shortly before its original patent expired in 2003.

France-based Sanofi sued Apotex for patent infringement because Sanofi researchers had separated Plavix's two main molecules and successfully applied for a second patent on just the effective molecule in the drug.

Apotex argued that the second patent, which doesn't expire until 2011, shouldn't have been granted. Two years ago the Supreme Court ruled in KSR v. Teleflex that a patent can't be awarded to the results of a procedure that is "obvious to try."

But both a U.S. judge in New York and the U.S. Court of Appeals for the Federal Circuit in Washington upheld the patent's validity, ruling that the results of the drug tests couldn't have been predicted, even if trying the experiment itself were obvious.