The rumour mill was in overdrive over the weekend over the continuing will they-wont they saga between Sanofi-Aventis and Genzyme, with sources cited by various media reports claiming the French drugmaker may up its bid for the US biotech in order to get due diligence started.

The two drugmakers are in talks over the potential use of a contingent value right (CVR) - under which the buyer makes additional payments if future milestones are reached - linked to Genzyme's leukaemia drug Campath (alemtuzumab), which is also in late-stage development for multiple sclerosis.

Differences in opinion between the two companies on the potential future sales of Campath has thus far proved to be a major stumbling block for the deal, with Sanofi basing its offer on extra revenues of around $700 million a year following approval for MS, but Genzyme forecasting turnover of around £3.5 billion by 2017.

According to people close to the situation cited by Bloomberg, Sanofi is considering raising its $69 a share offer by around $2 to tempt Genzyme into allowing it access to its accounts, but only if the matter of the CVR for Campath, which could reportedly be worth up to $6 a share, is settled beforehand.

Unsurprisingly, the Paris, France-based drugmaker is remaining tight lipped over its intentions, saying only that its financial advisors have been engaged in discussions with respect to a potential CVR for Lemtrada with milestone payments based upon approval and certain sales thresholds".   

But it also stressed that there remain "significant differences on the terms and conditions of the potential CVR and the value of our offer, and there is no guarantee that the parties will come to an agreement", indicating that there is still significant ground to cover before the companies can link hands.