Shares in Belgium's Solvay have fallen this morning on the news that partner Wyeth has terminated the firm’s collaboration on the investigational schizophrenia drug bifeprunox.

Solvay's shares were down 3.3% to 81.51 euros at 10.05am after it was confirmed that Wyeth is pulling out of the agreement signed in 2004 that also covered two early-stage compounds, SLV313 and SLV314, as well as bifeprunox. Claus Steinborn, executive vice president of global R&D at Solvay, said that the firm “of course respects Wyeth’s decision’, claiming that “this successful collaboration brought the compounds to their current stage of development”. He added that “we will add the compounds again to Solvay’s portfolio and analyse all options”.

Wyeth was a bit more forthcoming about its reasons for pulling out of the agreement. It said that the decision had been taken “after assessing the opportunity for bifeprunox and determining it would not have sufficient commercial value for the two companies to share". All development and commercialisation rights in North America will now revert to Solvay.

There had been concerns about bifeprunox since August last year when Solvay and Wyeth received a non-approvable letter from the US Food and Drug Administration which ruled that the compound was not approvable. The Belgian firm subsequently said it believed it would have to carry out a new trial that would probably take two years.

Solvay has also been planning to seek approval for the drug in Europe with Denmark's Lundbeck as its partner but observers are now worried that bifeprunox may be dropped altogether. The company had hoped that the drug would be a major growth driver in the future.