What Is Ambrisentan (Letairis)? Uses, Dosage, and What You Need to Know in 2026

Ambrisentan — sold under the brand name Letairis — is an FDA-approved medication for adults with pulmonary arterial hypertension (PAH). It belongs to a class of drugs called endothelin receptor antagonists (ERAs) and works by relaxing the blood vessels in the lungs to make it easier for your heart to pump blood. This guide covers everything you need to know about ambrisentan as a patient or caregiver in 2026.

What Is Ambrisentan Used For?

The FDA approved ambrisentan (as Letairis) in June 2007 for the treatment of pulmonary arterial hypertension (PAH, WHO Group 1) in adults. Specifically, it is indicated:

To improve your ability to exercise and delay clinical worsening of PAH when used alone

In combination with tadalafil (Adcirca) to reduce the risk of disease progression and hospitalization and to improve exercise capacity

PAH is a serious, progressive disease in which the arteries carrying blood from the heart to the lungs become narrowed, stiff, or blocked. This forces the right side of the heart to work much harder than normal. Ambrisentan does not cure PAH, but it helps slow its progression and improve quality of life.

What Are the Brand and Generic Names?

Generic name: ambrisentan

Brand name (U.S.): Letairis (manufactured by Gilead Sciences)

Generic manufacturers: Apotex, Cipla USA, Mylan, Sun Pharma, Teva, Zydus (all FDA-approved generic versions)

Drug class: Endothelin receptor antagonist (ERA), selective for the ETA receptor

Dosage: How Is Ambrisentan Taken?

Ambrisentan is taken by mouth as a tablet, once daily. It comes in two strengths: 5 mg (pale pink) and 10 mg (deep pink). Here is how dosing typically works:

Starting dose: 5 mg once daily

Dose increase: Your doctor may increase to 10 mg once daily after 4 weeks if the 5 mg dose is tolerated

Maximum dose: 10 mg per day

With food: Can be taken with or without food

Tablet handling: Swallow whole — do not crush, chew, or break. Pregnant women should also avoid handling broken tablets.

If you take cyclosporine, the maximum dose of ambrisentan is 5 mg once daily due to a drug interaction that roughly doubles ambrisentan exposure.

Who Should NOT Take Ambrisentan?

Ambrisentan is contraindicated (not safe to use) in the following situations:

Pregnancy — ambrisentan causes serious birth defects (boxed warning)

Idiopathic pulmonary fibrosis (IPF) — clinical trials showed it was harmful in this population

Known allergy to ambrisentan or any ingredient in the tablet

Moderate to severe hepatic (liver) impairment — ambrisentan is not recommended

What Does Ambrisentan Do for PAH?

In clinical trials (ARIES-1 and ARIES-2), patients taking ambrisentan walked 30 to 50 meters farther in a six-minute walk test compared to patients on placebo. They also experienced fewer PAH clinical worsening events. In the AMBITION trial combining ambrisentan plus tadalafil, the combination reduced the risk of clinical failure by 50% compared to either drug alone. These are meaningful improvements for people managing a life-limiting condition.

How Long Does It Take to Work?

Some patients begin to notice improvement in their ability to exercise within 1 month of starting ambrisentan. The greatest benefit in clinical studies was seen after 3 months of treatment. Ambrisentan is a long-term medication — most PAH patients take it indefinitely as part of their ongoing treatment plan.

What If I Miss a Dose?

If you miss a dose, take it as soon as you remember — unless it is nearly time for your next scheduled dose. In that case, skip the missed dose and resume your regular schedule. Do not take two doses at the same time to make up for a missed one.

If you ever have trouble filling your ambrisentan prescription, medfinder can contact pharmacies near you to find which ones have it in stock. To learn more about how ambrisentan works in the body, read our guide on ambrisentan's mechanism of action.