April 16 (Bloomberg) -- Sanofi-Aventis SA urged Canada's highest court to maintain existing patent laws and protect its blood-thinner Plavix from generic competition, saying the medicine resulted from four years of research.

``It takes a lot of work'' to bring such a drug to market, Sanofi lawyer Anthony Creber told seven judges on the Supreme Court of Canada panel in Ottawa today. Sanofi spent millions of dollars and even abandoned the project before discovering the compound that led to the development of Plavix, he said.

Canadian drugmaker Apotex Inc. contends that Sanofi's patent, which expires in 2012, doesn't contain a new invention. Apotex lawyer Harry Radomski said Sanofi scientists used known research methods on a group of 250,000 compounds the company had patented earlier to come up with the key ingredient in Plavix, known as the doctrine of selection.

``The doctrine of selection is contradictory to established principles of patent law,'' Radomski said. He urged the judges to abolish the practice that allows companies to patent a large group of compounds and then obtain new patents on individual components that prove useful.

Plavix is the second-biggest seller for Paris-based Sanofi. The company is attempting to prevent more competition after a brief entry into the market by Apotex in 2006 caused as much as $1.75 billion in lost sales for Bristol-Myers Squibb Co., which markets the drug in the U.S. under an agreement with Sanofi.

Apotex, which lost at the U.S. trial level, is fighting for the right to sell a generic version of the drug. Plavix last year regained its title as the world's second best-selling drug, behind Pfizer Inc.'s Lipitor, with $8.1 billion in global sales.

Expired Patent

Apotex claims that clopidogrel bisulfate, the active ingredient, was covered by a patent that expired in 2003. Sanofi maintains that the earlier patent covered a whole class of compounds and the discovery of clopidogrel bisulfate was a surprise.

Researchers separated a compound into mirror images, with one half providing the anti-clotting benefits and the other half containing toxic elements that caused convulsions, Sanofi said.

Bristol-Myers reported $4.76 billion in Plavix sales last year, making it the company's biggest product. Its 2006 sales were $3.26 billion because Apotex flooded the market with a six- month supply of the drug during a three-week period.

Sanofi, which sells Plavix outside the U.S., reported 2.42 billion euros ($3.7 billion) in sales from the medicine last year. Sanofi's biggest drug is the anti-clot medicine Lovenox.

Research Stifled

Abolishing the principle of the doctrine of selection would stifle research and innovation, Creber said. He was supported by lawyers for Canada's Research Based Pharmaceutical Companies, a national association representing workers in the industry, and BIOTECanada, an industry lobby group.

``The United Kingdom and the U.S. are countries where there is a lot of innovation going on,'' Justice Marshall Rothstein said, before the panel announced it would reserve a decision. ``Why would it be improper for us to consider that?''

U.K. and U.S. laws make it more difficult than in Canada to patent individual compounds taken from a larger group. The U.S. Supreme Court gives companies challenging patents more latitude to argue that something is simply an obvious variation of earlier inventions. Radomski urged the Canadian judges to only allow such patents if companies come up with new uses for the compounds.

``Please don't change the law,'' Creber said. ``It works well.''

The case is Apotex Inc. vs Sanofi-Synthelabo Canada Inc., 31881, Supreme Court of Canada (Ottawa).

To contact the reporters on this story: Joe Schneider in Toronto at jschneider5@bloomberg.net

Last Updated: April 16, 2008 13:58 EDT