Nov 25 (Reuters) - Merck ( MRK ) said on Monday its

drug, Winrevair, helped significantly reduce the risk of death

in patients with a rare condition which causes high blood

pressure in the lungs, months after it secured approval in the

United States.

Winrevair was approved to treat pulmonary arterial

hypertension (PAH), a progressive disorder caused by a

constriction of arteries in the lungs, leading to symptoms such

as shortness of breath, chest pain and dizziness.

Merck ( MRK ) said its drug met the main goal of significantly

reducing the time to disease worsening, lung transplantation or

death in a late-stage study of 172 patients with advanced stages

of the condition, already receiving background treatment.

The condition affects about 40,000 people in the United

States.

An independent data monitoring committee has recommended the

study be stopped early but participants would be able to

continue receiving the treatment, Merck ( MRK ) said.

Winrevair, which costs around $238,000 annually, was the

first treatment to secure approval from the U.S. Food and Drug

Administration from a class of drugs, which target a type of

protein called activin.

The drug brought in sales of $149 million for Merck ( MRK ) in the

third quarter amid concerns around bleeding risks in patients.

"We think Winrevair's efficacy outweighs safety risks in

severe patients - whom it is likely going to be limited to,"

Oppenheimer analysts said in a note earlier this month.