Elan Corp has dropped a bit of a bombshell by revealing that its recent link-up with Johnson & Johnson could also give the latter an option to acquire the 50% stake held in the multiple sclerosis drug Tysabri held by the Irish firm’s partner Biogen Idec.

Earlier this month, Elan sold an 18.4% stake in the firm and the rights to its portfolio of Alzheimer’s disease investigational drugs to Johnson & Johnson in return for $1 billion. However it appears that the deal also includes possible future access to Tysabri (natalizumab), which had second-quarter sales of $253.8 million; Elan’s share was $173.7 million.

Under the terms of the Elan and Biogen joint venture, each company has the option to acquire full rights to Tysabri should there be a change of control at either firm. Speaking on a conference call discussing Elan’s second-quarter earnings, chief financial officer Shane Cooke noted how J&J could become involved.

He noted that if something happens at Biogen, “and given the very significant value of Tysabri, it would be very difficult for us on our own to fund its purchase”. As a result, Elan has entered into a financing arrangement with J&J “that is relevant only should there be a change of control at Biogen”, which gives the US healthcare giant “the right to finance our purchase of the other half of Tysabri”.

If J&J exercised that right, Mr Cooke said that Elan would then enter into a 50/50 collaboration with J&J. “We’re delighted with this aspect of the arrangement, as it potentially gives us great flexibility in the event of a change of control at Biogen”, he added.

All of this is relevant only if there is a change of ownership at Biogen, which is not out of the question. The company was inviting approaches a couple of years ago but took the ‘for sale’ sign down in December 2007, a move which annoyed Carl Icahn. The billionaire investor has recently strengthened his position on Biogen’s board and while an imminent sale is highly unlikely, it is a tactic that Mr Icahn has pursued with some success of late.

Analysts believe that the arrangement with J&J suits Elan perfectly as it pretty much takes away any uncertainty about its Tysabri partner if anything happens at Biogen.