Shares in Sanofi-Aventis SA are trading near a low for the year amid new reports that the French pharmaceutical giant is close to launching an $18 billion takeover offer for U.S. biotechnology firm Genzyme Corp.

Around midday Tuesday Sanofi-Aventis shares were unchanged at 45.40 euros ($59.35). The stock has fallen nearly 6 percent over the last month since speculation emerged that Sanofi-Aventis was eyeing Cambridge, Mass.-based Genzyme, maker of the Cerezyme and Fabrazyme drugs to treat genetic diseases.

Earlier Tuesday the Wall Street Journal reported that Sanofi-Aventis had sent a letter to Genzyme detailing an offer of $69 a share, which would value the company at $18.4 billion.