FDA rejects expanded use of Vertex cystic fibrosis drug

The U.S. Food and Drug Administration has denied the expanded use of Vertex Pharmaceutical Inc's bestseller, Kalydeco, in certain cystic fibrosis patients, the company said on Friday.

The regulator rejected the company's application for using the drug in cystic fibrosis patients aged 2 or older, who have one of 23 residual function mutations.

Cystic fibrosis is caused by defects in the CFTR gene that disrupts the function of the lungs and digestive system, producing a build-up of thick, sticky mucus leading to inflammation and recurrent bacterial infections. Most patients die in their mid-20s.

Kalydeco, which brought in revenue of $632 million in 2015, is already approved to treat CF patients aged 2 and older with 10 different mutations in the CFTR gene.

The company was exploring the use of the drug in the group of 23 residual function mutations, also known to carry the CFTR protein.

Vertex said it had filed for an application based on studies of these mutations in preclincal trials and an exploratory mid-stage study.

The FDA informed Vertex that it cannot approve the application in its present form. The company said it would meet with the regulator to determine the path forward.

Vertex's shares were down 2 percent at $90 in premarket trading.

(Reporting by Amrutha Penumudi in Bengaluru; Editing by Maju Samuel)