Shares in Lundbeck have fallen to a three-year low after president and chief executive Claus Braestrup unexpectedly resigned just a day after the Danish firm posted its strongest-ever set of financial results.

The company’s stock fell for the third day on the trot to close down 6% to 106 kroner per share at market close. Lundbeck’s chairman Per Wold-Olsen, who will assume the role of executive chairman until a new CEO is appointed, said “it is regrettable that Claus Braestrup has decided to resign from his position sooner than we had expected”, noting that his departure from the firm is immediate.

Mr Wold-Olsen noted that the departing CEO had disclosed his intention to retire after Lundbeck had announced its financial results for 2007, though not quite so quickly. “The process of identifying in-house and external candidates is therefore well underway, and we expect to announce the name of Lundbeck's new president and CEO within the next couple of months," he added.

The chairman concluded by praising Mr Braestrup’s efforts, saying that he has been instrumental in building the firm's R&D activities (a division he previously headed), “the proof of which we are currently witnessing in the form of the largest and broadest pipeline of pharmaceutical candidates in development in Lundbeck's history”. However it is this pipeline that is causing concern.

The full-year results were impressive but the company’s task is now to reduce its reliance on the blockbuster Lexapro (escitalopram), sold in the USA by Forest Laboratories, and Lundbeck's own Cipralex brand of the antidepressant. Patents in for the drugs will expire in the USA in 2012 and in Europe two years later.

Lu AA21004 for depression has moved into Phase III trials, and the insomnia treatment Circadin (melatonin), licensed-in from Israel's Neurim Pharmaceuticals, should be launched in Europe later this year. Lundbeck still hopes for approvals of the investigational stroke drug desmoteplase, which failed a late-stage trial last June, but analysts are concerned that the pipeline will not be strong enough to fill the escitalopram gap.