Actelion and GlaxoSmithKline have revealed this morning that they are discontinuing development of their late-stage insomnia drug almorexant due to tolerance concerns.

The companies issued a statement saying they are pulling almorexant, a dual orexin receptor antagonist, following a review of data from additional clinical studies, which were conducted to further establish its clinical profile, "including the tolerability profile". However the partners say they "remain committed to conducting further research to better understand the potential of orexin receptor antagonism in sleep disorders and other indications". 

News of the termination is a particular blow for Actelion which is looking to reduce its reliance on the pulmonary arterial hypertension blockbuster Tracleer (bosentan). The drug accounts for the vast majority of the Swiss biotech's revenues but will start losing patent protection in 2015.

However the end of almorexant has not led to a slump in Actelion's share price. Long regarded as a takeover target, despite chief executive  Jean-Paul Clozel's repeated statements that the firm prefers to remain independent, analysts believe that Actelion's value lies in its PAH  franchise.