Billionaire investor Carl Icahn has fired off another letter to Amylin Pharmaceuticals and filed a lawsuit against the diabetes specialist in which he holds an 8.9% stake.

Last week, Mr Icahn criticised Amylin for not confirming or denying reports that the company recently turned down a $3.50 billion unsolicited takeover offer from Bristol-Myers Squibb. The high-profile investor, who believes the firm should be pursuing a sale, went on to attack the board for a public offering of 10% of the company at $15.62 per share and the granting of options to executives with an exercise price of $16.02 per share (27% below the rumoured B-MS $22 bid) on March 6.

Mr Icahn claims that this scenario "constitutes a dramatic change in circumstances requiring the board to permit shareholders another opportunity to nominate directors and make proposals at the 2012 annual meeting of shareholders. The deadline for this has passed but Mr Icahn demanded an extension, Amylin has ignored the request, so a complaint has been filed in a Delaware court.

The lawsuit alleges that Amylin "is a company at a crossroads and that stockholders should be entitled to nominate a new slate of directors committed to pursuing a sale of the company". Mr Icahn has also threatened the firm with another lawsuit if it does not produce copies of its books and records by Wednesday.

Amylin 'continually considers all options'

Amylin sent a statement to PharmaTimes World News saying that "we believe Mr Icahn's lawsuit is without merit," adding that the board is "fully aware of its fiduciary duties". The 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, says it "continually considers all options available and is relentlessly focused on creating the greatest value for our stockholders".