Sanofi-Aventis has once again extended its offer to acquire Genzyme Corp and is not raising its $18.50 billion bid, at least not for the timebeing.

The French drugmaker is sticking with its $69 per share offer which is now scheduled to expire on February 15, having ended last Friday. This is the second extension Sanofi has announced as its first bid expired in December.

By Friday night, just  0.4% of Genzyme shares had been tendered, Sanofi said, down from the 0.9% offered up before the December deadline. This means that some sellers have retracted their shares as they wait to see what comes out of the ongoing talks between the two parties.

Sanofi reiterated that those talks centre around the "structure of a contingent value right" (CVR) involving Lemtrada (alemtuzumab) for multiple sclerosis "as an element of any potential transaction". The drug is already sold as Campath for leukaemia.

Sanofi believes Genzyme has overplayed the future sales of Campath in MS, believing that $700 million is a more likely figure than the $3.70 billion by 2017 that Genzyme chief executive Henri Termeer forecast last year. The Paris-based group noted that although discussions have continued and have included commercial teams and executives of both firms, "there remain significant differences on the potential CVR and the value of Sanofi's offer and there is no guarantee that the parties will come to an agreement". 

Nevertheless, most analysts believe Sanofi is unlikely to pull out of any deal and a raised offer could come out of the discussions.