It aims to lower the risks of disease progression and hospitalization for worsening PAH, and enhance exercise ability.
The approval followed a study in which the Letairis/tadalafil combination achieved better results instead of using either drug individually.
Letairis was first approved for PAH treatment in 2007.
It claims to reduce the risk of disease progression by about 50% compared to either therapy individually in the study of 605 PAH patients with WHO Functional Class II-III symptoms.
The double-blind, multicenter AMBITION study was cosponsored by Gilead and GlaxoSmithKline (GSK).
Eli Lilly and Company has also provided funding and tadalafil drug supply for the trial.
Gilead commercializes ambrisentan under the tradename Letairis in the US and GSK commercializes it under the tradename Volibris in territories outside of the US.
University of California, Los Angeles professor Ronal Oudiz: "The evidence to support the use of [Letairis] and tadalafil in PAH is well-established, however an outstanding question has been whether combining these two medications up front may further delay the progression of this disease over the long term for patients who are newly starting PAH therapy."
PAH is characterized by constriction of the blood vessels in the lungs, resulting in high pulmonary arterial pressures, which make it difficult for the heart to pump blood via the lungs to be oxygenated.
Patients with PAH suffer from shortness of breath. It can occur with no known underlying cause, or secondary to diseases like connective tissue, congenital heart defects, cirrhosis of the liver and HIV infection.