Certificates related to Sanofi-Aventis's $20.1 billion acquisition of U.S. biotech firm Genzyme could begin trading on Nasdaq as soon as April 4, depending on the outcome of its tender offer.

The French drugmaker said on Tuesday that the U.S. Securities and Exchange Commission (SEC) had cleared the trading of contingent value rights (CVR) under the ticker.

Sanofi-Aventis clinched its long-sought deal to buy Genzyme in February with a sweetened offer that comprises cash and the possible payment under the CVRs of additional amounts geared to the future performance of several of the U.S. group's drugs.

Sanofi's improved tender offer of $74 a share plus one CVR per share will expire just before midnight New York time on April 1. The offer could be extended should Sanofi fail to get at least 50% of Genzyme's shares.

Genzyme shareholders could receive one-time milestones and payments if production levels of two of Genzyme's key rare disease drugs Cerezyme and Fabrazyme are met following a shortage due to contamination problems at a manufacturing plant.

Other milestone fees depend on whether Genzyme's multiple sclerosis drug Lemtrada wins U.S. marketing approval and if sales of the drug hit specified targets.