Apotex has been unsuccessful in its bid to secure the rights to market a generic version of Sanofi-Aventis’ blockbuster blood thinner Plavix (clopidogrel) in Canada.

The Supreme Court of Canada unanimously upheld the validity of Sanofi’s Plavix patent, which is not due to expire until 2012.

Apotex had claimed that Sanofi was protecting the drug’s patent by “evergreening”, a strategy that allows companies to extend their patents forever.

The French drug giant was said to be doing this by a process known as “the doctrine of selection”, Apotex said, whereby a large number of compounds are patented before individual components are selected for use and new patents obtained for these.

Sanofi and US marketing partner Bristol-Myers Squibb sued Apotex for patent infringement in March 2002 but a statutory stay of the latter’s application with the US Food and Drug Administration to make a generic form expired in 2005, prompting Apotex to start selling its generic version of Plavix.

An attempted settlement was rejected a year later and in May 2007 B-MS pleaded guilty on two counts of making false statements to the US Federal Trade Commission concerning the botched settlement and agreed to pay a $1 million fine.

The fall-out cost the jobs of senior B-MS management, including the chief executive Peter Dolan, and caused up to $1.75 billion in lost sales.