Adults age 18 and older may use Letairis to treat pulmonary arterial hypertension (PAH). This prescription medicine is a type of endothelin receptor antagonist and works by blocking the action of certain proteins in the body that cause the blood vessels to constrict. Letairis helps to improve PAH symptoms and slow down the progression of the disease.
Letairis® (ambrisentan) is a prescription medication approved for the treatment of pulmonary arterial hypertension (PAH), a condition that affects the heart and lungs. It belongs to a group of medicines known as endothelin receptor antagonists.
People with PAH have abnormally high blood pressure in the pulmonary arteries. The pulmonary arteries are the blood vessels that carry deoxygenated blood (blood without oxygen) from the right side of the heart to the lungs. The blood picks up oxygen from the lungs, returns to the left side of the heart, and is then pumped to the rest of the body. The cells of the body use the oxygen for energy.
In PAH, the pulmonary arteries become narrowed, making it more difficult for blood to flow through them. As a result, pressure inside the arteries increases, and the heart is forced to work harder to pump the blood to the lungs. This puts strain on the heart. Over time, the strained heart enlarges, weakens, and eventually fails.
There are several different types of PAH, depending on the underlying cause of the condition. These types include:
- Idiopathic PAH, in which the cause is unknown
- Heritable PAH (also referred to as genetic PAH), which is passed through families and is related to certain abnormal genes
- Associated PAH, which is caused by other conditions, such as connective tissue disease, congenital heart disease, or liver disease.
People with PAH may not have any symptoms at first. Symptoms usually begin to occur when the heart is no longer able to pump enough blood to the body. As the disease progresses, the symptoms gradually become worse. Common symptoms of PAH include:
- Shortness of breath, especially when exercising
- Dizziness or fainting
- Chest pain
- Swelling in the legs, ankles, or abdomen (stomach)
- A fast heartbeat.
One way healthcare providers assess the severity of PAH is by determining how much the symptoms affect everyday activities. They then use this information to categorize a person into one of the following four groups:
- Class I -- No limitation on activity. A person in this class has no symptoms with exercise or at rest.
- Class II -- Slight limitations. In this class, ordinary activities cause some symptoms, but there are still no symptoms at rest.
- Class III -- Marked limitation. A person in this class will have symptoms with less-than-normal activity.
- Class IV -- Severe limitation. Symptoms occur with any activity and even at rest.
Because the system for classifying PAH severity was developed by the World Health Organization (WHO), the categories are often referred to as WHO Classes I through IV. Interestingly, the system was adapted from a similar system developed by the New York Heart Association (NYHA) for classifying heart-failure severity.
PAH is a progressive condition, which means it gets worse over time. Unfortunately, there is no cure for the condition. Treatment is aimed at slowing down the progression of the disease and controlling symptoms.
Letairis has been studied for use in people with functional Class II or III PAH symptoms. The majority of people in Letairis clinical studies had idiopathic PAH, heritable PAH, or PAH associated with connective tissue disease. In these studies, the medication was shown to improve exercise ability, which was assessed by determining how far a person could walk in six minutes. People taking the medication were also less likely to have their condition get worse.