Biogen Idec has announced it is seeking a buyer for the company and has already received several expressions of interest - including a reputed $23bn (€16.2bn) bid from billionaire corporate raider Carl Icahn. The US biopharma company will "determine whether potential strategic interest on the part of major pharmaceutical companies might result in superior value [for stockholders]". Many industry insiders are not surprised about the announcement. Icahn recently announced he held a 1 per cent share in Biogen and in August, he received the legal go-ahead to increase that stake. How much he planned to buy or how much he now owns is unknown, but that didn't stop speculation he might try and buy the company outright, or force it to be sold. It was a similar story with MedImmune: three months after he announced he held a 1 per cent stake in that company, it was sold to AstraZeneca amid stories that Icahn had pressurised it into selling up. Meanwhile Biogen is insisting it doesn't need to sell and an acquisition isn't certain. It said its strategy is "working and generating strong operating and financial performance." The news has caused Biogen shares to rocket up 17 per cent to $81.60 in after-hours trading. That's an all time high and would give the company a market capitalisation around $23.5bn. According to a report on Bloomberg, Icahn has already made a bid of $23bn and believes the company is worth more. A potential stumbling block to any deal is Biogen's partnership with Elan over the multiple sclerosis (MS) drug Tysabri (natalizumab). The companies share ownership of the drug 50-50 and although it was withdrawn from the market only three months after approval, it has now been reintroduced and is making a comeback. As of the end of September 2007 approximately 17,000 patients are on Tysabri worldwide, according to Biogen. However, Icahn reportedly told Bloomberg that Elan won't block any bid for Biogen. Should a sale go ahead, Elan has several options: it has the right to acquire for fair value the 50 per cent economic interest in Tysabri currently held by Biogen; under certain circumstances, the ability to sell its 50 per cent stake in the drug; or, to continue with the existing agreement. Elan said today that it has hired Lehman Brothers to advise it on these options. The two companies have also announced today that US Food and Drug Administration (FDA) will extend its regulatory review of the drug as a treatment for Crohn's disease by up to 3 months. The regulators require additional time "to review information regarding the proposed Tysabri risk management plan for Crohn's disease," said Elan. Under this revised timeline, the companies anticipate action from FDA on or before January 13, 2008.