Genzyme Corp is reportedly looking at ways of breaking the stalemate over the hostile takeover bid made by Sanofi-Aventis that would see the French drugmaker, or any other buyer, make additional payments depending on the success of its drugs in the future.

Genzyme Corp has repeatedly rejected Sanofi's $18.50 billion, or $69.00 per share, hostile offer but the Wall Street Journal, citing people "familiar with the matter," says the US biotech is  exploring the possibility of a contingent value right (CVR) being added to any deal. A CVR means that the purchase price would be supplemented by extra payments in the future, in this case reflecting the potential of Campath (alemtuzumab),  Genzyme's leukaemia drug which is in late-stage trials for multiple sclerosis.

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 has forecast.

The WSJ claims that Sanofi has indicated it would be open to a CVR, although Genzyme believes that using said mechanism is not enough on its own to break the impasse if the $69.00 per share offer is not raised. The newspaper goes on to say that Genzyme has also been integrating the CVR in its discussions with third parties who may be interested, including Pfizer, Johnson & Johnson and Merck & Co.

CVRs have been used before in pharma deals, the WSJ notes. It cites Celgene Corp's $2.90 billion deal for Abraxis BioScience in July, which included the potential for extra payments of around $650 million dependent on various regulatory approvals of the cancer drug Abraxene, an albumin-bound formulation of paclitaxel.