PARIS ( TheStreet) -- Sanofi-Aventis ( SNY) CEO Chris Viehbacher has support from the board to offer as much as $70 a share for Genzyme ( GENZ), or about $18.7 billion, Bloomberg reports. Sanofi, France's largest drugmaker, is preparing a formal approach, and plans to send a letter to Genzyme in a few days that will detail its interest and give a specific price, said three people with knowledge of the situation, Bloomberg reports. The CEO declined to comment on Genzyme in a conference call with reporters Wednesday. "We can't comment on specific speculation," he said, after announcing that Sanofi earnings rose 61% in the second quarter. Genzyme, the world's largest maker of medicines for genetic diseases, last week rebuffed an informal approach by Sanofi to enter talks, said people familiar with the situation, according to Bloomberg. Genzyme shares closed Wednesday at $68. -- Written by Joseph Woelfel in New York. Get more stock ideas and investing advice on our sister site, Stockpickr.com.