PARIS (AP) – France's Sanofi-Aventis on Monday launched an $18.5 billion hostile takeover offer for Genzyme Corp., stepping up its effort to capture the U.S. biotech company's promising drugs for high cholesterol and lucrative treatments for rare genetic disorders. At $69 per share, the offer for Genzyme, based in Cambridge, Massachusetts, is unchanged from a friendly bid that Sanofi-Aventis made privately to management in July and publicly disclosed in August, only to be rejected. It's the biggest hostile takeover in the pharmaceutical industry since Roche Holding's 2008 acquisition of Genentech for $47 billion, according to Dealogic, which analyzes mergers and acquisitions. Sanofi-Aventis CEO Chris Viehbacher, on a conference call with reporters, said he decided to go straight to shareholders because Genzyme management ""refused to engage in constructive discussions"" despite several attempts by Sanofi-Aventis. The offer to Genzyme shareholders opens Monday and runs to Dec. 10. Viehbacher said he has met with shareholders holding more than 50 percent of Genzyme's capital and that he is ""confident the offer will be successful.""