France's Sanofi Aventis said on Wednesday that it had received the green light from U.S. antitrust regulators to take-over the U.S. biotech Genzyme. Sanofi said that the waiting period under the Hart-Scott Rodino antitrust improvements act of 1976 had expired. The act puts a waiting period on all mergers in the U.S. so that federal authorities can inspect them for obvious antitrust violations.

On Oct. 4 Sanofi-Aventis took a $69 per share offer for Genzyme directly to shareholders, after management refused to come to the table and discuss a friendly takeover. The bid, widely seen as an opening offer to induce Genzyme to open its books, expires just before midnight on Dec. 10. Should Genzyme management continue to refuse to negotiate, the battle to take over the company could be prolonged and result in a proxy battle.

Sanofi aims to acquire Genzyme's lucrative portfolio of drugs for rare diseases as it prepares for the loss of patent protection on top-selling drugs, such as its biggest product, the blood clot preventer Plavix.