Actelion has suffered a setback in its quest to expand the uses of Tracleer follow-up Opsumit, after a study assessing the drug in patients with pulmonary arterial hypertension (PAH) due to Eisenmenger Syndrome failed to meet its primary goal.

MAESTRO (MAcitentan in Eisenmenger Syndrome To RestOre exercise capacity) was a Phase III multi-center, double-blind, randomised, placebo-controlled, parallel-group study to evaluate the effects of Opsumit (macitentan) on exercise capacity in patients with the condition.

Results showed that, after 16 weeks of treatment, the mean change in six-minute walk distance (6-MWD) from baseline was an increase of 18.3m in the Opsumit group and 19.7m in the placebo group. While this signalled a treatment benefit, the difference was not significant.

However, Professor Nazzareno Galiè, head of the Pulmonary Hypertension Center at the Institute of Cardiology, University of Bologna, and Steering Committee member for the MAESTRO study,
said he believes the result was "influenced by an unexpected improvement in the placebo arm of the study, which is unusual in a predominantly untreated PAH population".

A full analysis of the results is needed to understand the data, he stressed.

While disappointing, analysts don't believe the trial's failure will interrupt any potential deal between Actelion and Johnson & Johnson. The two parties have been locked in "exclusive discussions" over a potential strategic transaction since December.