Shares in Amylin Pharmaceuticals leapt over 8% after a report from Bloomberg claimed that Sanofi and Merck & Co have made initial takeover bids for the diabetes specialist.

The news agency cites three people familiar with the process that the two drug giants have made offers of at least $25 a share, which values Amylin at more than $4 billion. Last month, it was reported that the latter which recently was rumoured to have rejected a hostile $3.50 billion, or $22 per share, bid from Bristol-Myers Squibb, had signed up Credit Suisse and Goldman Sachs to sound out potential buyers.

The Bloomberg sources added that B-MS is expected to come back with another offer and Takeda Pharmaceutical Co also indicated it will make a bid. Pfizer, AstraZeneca and Roche have also reportedly signed confidentiality agreements although it is not clear whether they have decided to move ahead with offers.

Following the rumoured B-MS bid, the Amylin board was criticised by billionaire investor Carl Icahn, who holds an 8.9% stake, for not pursuing a sale. Management of the firm, which is in the process of ending its long-time collaboration with Eli Lilly for the big-selling diabetes drug Byetta (exenatide) and its once-weekly successor Bydureon, previously said it is looking to work with "one or more partners" outside the USA. However, a sale is looking more likely.

The Bloomberg report quoted Phil Nadeau, an analyst at Cowen & Co, said that for most of the potential buyers that have been mentioned, "Amylin would be complementary to what they have”. He went on to say that each of these has a diabetes franchise and sales force "and has been successful to some extent in the past. They could presumably make Bydureon a bigger product than Amylin is making it".