* Macitentan company's big hope as Tracleer nears end of patent
* Drug improved walking distance by 23 metres
* Reduced the risk of all-cause mortality by 36 pct
* Halved risk of death and hospitalisation due to PAH
ZURICH, Oct 24 (Reuters) - Actelion's experimental lung drug macitentan prolonged overall survival by more than a third according to detailed study data, which the company hopes will convince investors it has a viable follow-up product to secure its commercial future.
Europe's largest standalone biotech company wants the drug, which treats pulmonary arterial hypertension -- a disease that causes high blood pressure in the arteries of the lungs -- to replace blockbuster Tracleer.
Tracleer currently makes up 87 percent of sales but loses patent protection in 2015 and has also seen its market share eroded by Gilead's Letairis.
The latest data presented at a meeting of the American College of Chest Physicians in Atlanta late on Tuesday showed that a 10 miligram dose of the drug reduced the risk of all-cause mortality by 36 percent.
Actelion said this week it had filed macitentan - which it plans to sell under the brand name Opsumit - for U.S. regulatory approval. If the Food and Drug Administration grants the drug a priority review, a decision could be reached within eight months, spokesman Roland Haefeli said.
Analysts at Jefferies said a trend towards overall survival should be viewed as "sufficiently meaningful" for payers such as health insurers.
"Overall the detailed data at the very least underscore our confidence in macitentan's regulatory approvals and commercial future, together we believe with providing ample ammo to convince payers on favourable reimbursement/pricing," they said.
Jeffereies forecasts peak macitentan sales of $1.25 billion assuming a 40 percent patient share.
Pulmonary arterial hypertension (PAH) is a progressively worsening condition in which the arteries carrying blood to the lungs narrow, overburdening the heart and raising blood pressure. The cause is unknown and the disease has no cure.
The FDA this week rejected a potential rival PAH drug, telling United Therapeutics Corp that it was not sure if another clinical study would alter its impressions but it gave some guidance on what to do if the company decided to go ahead with one.
In the Actelion study, doctors were also scrutinising data which measures how far participants can walk in six minutes - a commonly used benchmark in trials for drugs of PAH that enables comparison with other therapies.
Patients on macitentan who took the 10 mg dose improved their walking distance by 23 metres.
Taking the drug halved the risk of death or hospitalisation due to PAH for those on a 10 mg dose and cut it by a third for those on 3 mg - a significant reduction as hard-pressed healthcare systems seek to cut costs by keeping patients out of hospital beds.
Actelion said in April that the drug decreased the risk of morbidity and mortality in comparison to a placebo by 45 percent in those patients given 10 milligrams of the drug and by 30 percent in those on 3 mg.
The company also plans to file macitentan for approval in the European Union in the fourth quarter. (Editing by Edwina Gibbs)