The FDA approved Gilead’s (GILD) drug Letairis (ambrisentan) for pulmonary hypertension.

The disease: Narrowing and thickening of pulmonary (lung) arteries cause an elevation of the patients’ blood pressure. Among the symptoms are shortness of breath and exhaustion, which makes patients unable to exercise, or walk distances. The disease could cause heart failure and could be fatal if not treated.

The drug: Letairis belongs to a class of drugs called ERAs, or endothelin receptor antagonists. It relaxes the arteries, lowering blood pressure, hence, decreasing the extra load on the heart and lungs. In experimentation, the drug improved patients’ capacity to exercise. The drug is indicated as a once-daily treatment of pulmonary arterial hypertension (WHO Group 1) in patients with WHO Functional Class II or III symptoms to improve exercise capacity and delay clinical worsening. Letairis will be available in the United States early next week. Because of the risks of liver injury and birth defects, the product will be available through the Letairis Education and Access Program (LEAP), a restricted distribution program designed to help patients learn about the risks of Letairis.

The drug’s label will carry strong cautionary language in a black box, as do other drugs of its class. Gilead says its studies show that incidence of liver damage is less with Letairis than with other products in this class. The company said Letairis will be available only through a special restricted program to educate patients and doctors about safe usage.

Price: Gilead said it has priced the drug at $3,940 a month, comparable with other oral drugs for the disease. Gilead said it established a program to ensure greater access to patients who are underinsured or face high co-payment requirements.

Incidence: Gilead said it estimates about 75,000 to 90,000 people in the US suffer from PAH, and 200,000 people worldwide, although fewer than half of them are currently believed to be diagnosed. The condition is often misdiagnosed as exercise-induced asthma or other respiratory ailments.

Marketing: Gilead in the US and GlaxoSmithKline PLC outside the U.S. Currently the drug is under regulatory review in Europe and Canada, and GlaxoSmithKline is doing studies in Japan aimed at getting approval there.

The Bad News

A drug developed by Encysive Pharmaceuticals (ENCY) for the same disease, i.e., pulmonary arterial hypertension, did not satisfy the requirements of the FDA for final approval. The agency issued its third approvable letter for the drug called Thelin, stating that Encysive’s development program did not demonstrate the evidence of effectiveness needed for approval.

Encysive said the FDA “encouraged the company to conduct an additional study” documenting that the drug improves exercise tolerance.

It is, indeed, bad news, especially, that in the same day, Gilead’s product was granted approval for the same disease.