French drugmaker Sanofi-Aventis has agreed to buy Genzyme Corp for $20.1 billion in cash, plus payments tied to the success of the company's drugs, the companies said on Wednesday.

Sanofi will pay $74 a share in cash and a contingent value right for the U.S. biotechnology company. The CVR is a tradable right to additional payments if Genzyme's multiple sclerosis drug, Lemtrada, reaches regulatory and sales targets or 2011 production volumes of Cerezyme and Fabrazyme are achieved.