French drugmaker Sanofi-Aventis has launched its multi-billion dollar blood thinner Plavix in Japan, the world's second largest pharmaceutical market, following its approval for secondary prevention in patients undergoing ischemic strokes earlier this year.

Sanofi will co-promote Plavix (clopidogrel) with Daiichi Sankyo Co. Last July, Daiichi Pharmaceutical and Sanofi-Aventis agreed to transfer all commercial rights for Plavix in Japan from Daiichi and their joint venture to Sanofi-Aventis Japan, for antitrust reasons. Daiichi's merger with Sankyo - which has the stroke drug prasugrel in its late-stage product pipeline - was the driver for the transfer, which completed in September 2005.

An estimated 2 million people suffer from cerebrovascular disease in Japan, making it the third major cause of death in the nation. Its availability in the country should add momentum to Plavix, which is already one of the pharmaceutical industry's fastest-growing blockbuster products, with sales up 21% to 580 million euros in the first quarter of 2006.

And Sanofi is working hard to protect its asset. Earlier this year, the firm and US partner Bristol-Myers Squibb said they had cut a deal with generic drumaker Apotex that could potentially keep a copycat version of their Plavix off the market until 2011.