French drugmaker Sanofi-Aventis  launched a hostile bid for Genzyme at $69 per share on Monday, taking its $18.5 billion offer direct to shareholders after Genzyme management refused to negotiate.

The move comes a month after Genzyme rebuffed an approach from Sanofi-Aventis at the same price. Sanofi has since been talking to Genzyme investors, who it said were frustrated by Genzyme management's intransigence.

Sanofi's unsolicited offer, all in cash, will expire on December 10 at 11:59 pm EST.

 'Sanofi-Aventis has a history of being a patient, disciplined buyer,' Sanofi Chief Executive Chris Viehbacher told reporters in a conference call. 'We believe the offer will be successful ultimately.'

Viehbacher, who wants to buy Genzyme to boost Sanofi's drug portfolio as sales of older medicines decline, said his strong preference was for friendly talks, but he had decided to start a tender offer because of Genzyme's refusal to enter discussions.

A Genzyme official at the company's US headquarters declined to comment.