Sanofi-Aventis, the French pharmaceuticals group, said on Tuesday it was facing a fresh legal challenge to its patents on Plavix, its best-selling drug, from its smaller Scottish rival Aircoat.
The challenge is the first to be launched against Sanofi's European patents on Plavix and will be heard by a Scottish court. But the French group said it believed "Aircoat's arguments to be without merit, and will vigorously defend its patent".
The Paris-based company, formed by last year's €54bn merger of France's two biggest pharmaceutical groups, is already facing a lawsuit in New York - due to start in March - to appeal against challenges to Plavix's US patents from Canada's Apotex and India's Dr Reddy’s.
Analysts say doubts over whether Sanofi can successfully defend the Plavix patent against generic drugmakers until it expires in 2011 are one of the biggest risks weighing on the share price of the new group.
The blood-thinning drug accounted for €2.96bn of Sanofi's total group sales of €18.78bn in the first nine months of last year. More than half of Plavix sales were in the US, where the French group sells the drug through a partnership with Bristol-Myers Squibb.
Plavix works by preventing accumulation of platelets in the blood, which form clots. It is used to reduce the risks of cardiovascular problems such as strokes.
The challenge from generic drugmakers in the US is based on the argument that the 2011 patent, based on work to isolate and refine the two isomers of the drug's key molecule as well as the four salts used to make it soluble, adds nothing new to the original patent that expired in 2003.
Sanofi-Aventis shares were flat at €57.95 on Tuesday morning. They have outperformed the global pharmaceutical index by about 15 per cent but slightly trailed behind the CAC-40 index of French blue chip companies since the Sanofi-Aventis merger was completed in August.