Europe's largest biotech company Actelion said it expects results of a key late-stage trial on heart and lung disease drug macitentan in the next few weeks after a strong Swiss franc and competition hit first-quarter profit.

Actelion is trying to cut its dependence on its main product Tracleer, which accounts for around 90% of group sales and is facing growing competition from Gilead's rival drug Letairis.

All eyes are on the results of the pivotal late-stage clinical trial of macitentan, billed as a Tracleer successor, which the company expects to be available in the next few weeks.

Its success is vital if Actelion is to protect its dominant position in the pulmonary arterial hypertension (PAH) market. Tracleer will lose patent protection from 2015.

"We continue to have high conviction in a positive outcome and expect a macitentan launch to allow Actelion to at least partially defend its PAH franchise from both competition from Gilead and from potential Tracleer generics over 2015-2017," Deutsche Bank analysts said in a note.

A successful trial could also boost shares in Actelion, which lost more than 35% of their value last year. Failure, however, could put the stock under further pressure as investors fret about competition to its franchise.

The company was embroiled in a boardroom battle last year with activist investor Elliott Advisors, who accused the Swiss biotech group of eroding shareholder value after a string of product setbacks.

Facing the headwinds

Analysts in a Reuters poll has forecast net profit to average 66.8 million Swiss francs. The miss was due in part to a $10 million payment to Auxilium Pharmaceuticals booked in the first quarter.

Last year's figures were also flattered by a 76.5 million franc payment in final recognition of deferred revenue from a GlaxoSmithKline collaboration.

First-quarter Tracleer sales slipped to 363.7 million Swiss francs from 402.8 million Swiss francs a year ago.

Top-selling Tracleer is under pressure as sales of rival drug Letairis pick up after U.S. health regulators removed warnings about potential liver damage last year.

"We are losing market share, but it's a very gradual loss. The wheels haven't fallen off the product," Chief Financial Officer Andrew Oakley told Reuters.

Actelion lifted its outlook, saying it now only expects sales in local currencies to decrease by a low single-digit percentage in 2012 after earlier guiding for a decline in the low-to-mid single digits.

The Basel-based firm was granted a reprieve from Japanese authorities, who left Tracleer pricing unchanged and also experienced a slightly better pricing environment in the United States.

Actelion said it remained on track for flat core earnings in 2012.