The news is another blow to Aventis, which is already dealing with a hostile takeover bid launched on Monday by French pharmaceutical firm Sanofi-Synthelabo.
Arava (leflunomide) was launched in Japan last September but is already sold in more than 70 countries worldwide. It achieved global sales of €271 million in 2002, but has just lost its patent in the US, and global sales of the product are expected to shrink to €250 million in 2003, according to analysts.
Sixteen patients in Japan have developed a serious respiratory condition called interstitial pneumonia after taking the drug, and in five cases this proved fatal. The company is still investigating whether the cases are definitely linked to the drug, although this form of pneumonia is a recognised though rare side effect with the product.
Interstitial pneumonia was also encountered in patients taking AstraZeneca's cancer drug Iressa (gefitinib) in Japan, but did not lead to the withdrawal of this drug from the market in Japan or impede its approval elsewhere.