* Sees 2014 core earnings up by low single digit
* 2013 net profit 453 mln Sfr vs 361 mln in poll
* Says Opsumit "very well received" in U.S.
* To pay dividend of 1.20 Sfr per share
* Shares rise 1.8 percent
ZURICH, Feb 11 (Reuters) - Actelion, Europe's biggest biotech company, raised its 2014 earnings forecast on Tuesday, encouraged by a strong launch for its new heart and lung drug and better-than-expected profit for last year.
The Swiss company has seen its prospects brighten after regulators in Europe and the United States approved its big drug hope Opsumit, a treatment for pulmonary arterial hypertension (PAH), at the end of last year.
It is banking on Opsumit to cut its dependence on mainstay drug Tracleer, which makes up around 86 percent of sales, but loses patent protection from 2015 and has faced growing competition from Gilead's Letairis.
Actelion said it had 5 million Swiss francs ($5.6 million) in sales for Opsumit since the drug was launched on the U.S. market in mid-November.
"The launch of Opsumit was better than we expected and therefore we have decided to raise our guidance," Chief Executive Jean-Paul Clozel told Reuters in an interview.
Actelion now expects a low single digit percentage increase in core earnings at constant currencies this year, compared with a previous forecast for at least stable core earnings. It has also forecast single digit core earnings growth for 2015.
Alongside Opsumit's approval, a big dividend increase and a late-stage study into another promising lung drug, selexipag, have helped to endear Actelion shares to investors, sending the stock up over 70 percent last year.
The shares, which trade at 21.1 times forecast earnings compared with a peer medium of 15.1 times, were up 1.8 percent in early trade at 91.35 francs, against a flat European healthcare sector index.
Actelion has launched Opsumit at the same price as Tracleer in the United States, hoping to ramp up sales quickly by grabbing market share from rivals.
Actelion is confident that Opsumit will achieve higher peak sales than Tracleer: "In my mind it's not really if, but it's when," Clozel said.
Analysts at brokerage Jefferies forecast peak annual sales for Opsumit of $2.2 billion.
Sales of Tracleer shrugged off pricing pressure in Europe and strong competition in the United States to rise 5 percent at constant exchange rates to 1.53 billon Swiss francs last year.
Actelion said it had launched Opsumit in Germany, at a 7 percent premium to Tracleer, at the end of January and was in the process of rolling it out in Britain, Austria and Denmark.
Investors are now turning their attention to Phase III trial results for selexipag, another PAH drug, which are expected in mid 2014. Clozel said he expected to file the drug for approval at the end of this year and anticipates a launch in 2015.
The company is also developing an antibiotic for patients suffering from Clostridium difficile associated diarrhoea and is currently enrolling patients for a late-stage trial.
Actelion posted full-year product sales of 1.78 billion francs, generating net profit of 453 million. Analysts in a Reuters poll had forecast product sales of 1.76 billion and net profit of 361 million.
The firm proposed a 20 percent increase in its dividend to 1.20 francs per share, ahead of analyst forecasts for 1.05 francs.