Actelion says it will not return to growth until 2014, guidance which has unnerved some investors, while targeting lower costs and building on the promise shown by its new pulmonary arterial hypertension drug macitentan.

Last week, Actelion shares soared on very positive Phase III data from the landmark SERAPHIN morbidity/mortality study with macitentan in patients suffering from PAH. The drug, a dual endothelin receptor antagonist, is seen as the successor to the firm's flagship drug Tracleer (bosentan), which brings in around 1.5 billion Swiss francs a year.

Tracleer goes off-patent from 2015 and is already struggling to hold market share against Gilead Sciences' rival drug Letairis (ambrisentan). Therefore, Actelion management, addressing analysts at a meeting in London,  predicted stable earnings in 2013, followed by a return to growth in 2014.

However, Actelion believes it will enjoy double-digit growth in 2015 thanks to macitentan and another PAH drug, selexipag, which is in a Phase III morbidity/mortality study. The firm also noted that its current clinical pipeline in immunomodulation and antibiotics gives it "an opportunity to build a second specialty business franchise, thus accelerating revenue growth and diversifying Actelion's risk profile".

This refocusing is expected to result in "lower and more targeted R&D spending, as well as lower overhead costs", in addition to its ongoing savings programme. Chief executive Jean-Paul Clozel said that "the strength of our pipeline and our renewed efforts to optimise profitability will produce a bright future for Actelion".

Investors were a little concerned by the tough couple of years ahead and Actelion's shares fell 3.8% to 38.47 francs.