Analysts have been weighing up the possible candidates to buy Biogen Idec and it would appear that pretty much every big pharma player could be interested while billionaire investor Carl Icahn has reportedly already offered $23 billion.

Biogen noted that Mr Icahn, who currently has a small stake in the firm, had indeed made a bid but did not reveal how much he has offered. He is likely to face some serious competition from the big players in the industry, however, many of whom have been talking about boosting their biological capacity.

The names in the frame include Pfizer, GlaxoSmithKline, and Sanofi-Aventis which spoke last month at its R&D meeting in Paris of the need to expand its presence in biotechnology. Two firms that seem less likely to make a bid are Roche and AstraZeneca, as the first firm is seen as a strong biologicals player while AstraZeneca has only recently splashed out on MedImmune.

However a fly in the ointment could be the deal that Biogen has in place with Elan for the multiple sclerosis drug Tysabri (natalizumab), a potential big earner which the Irish firm may claw back the rights for. This at a time when royalties from the rheumatoid arthritis and cancer drug Rituxan (rituximab), which come from Biogen's joint venture with Genentech, are declining.

All this may have the effect of reducing the price put on Biogen but with Mr Icahn hovering and big pharma eyeing up a reasonable pipeline and established marketed products, top dollar is sure to be asked by the firm's board.