A randomized, double-blind Phase III study of Vertex’s Kalydeco in 69 cystic fibrosis patients ages 6 and up with at least one R117H mutation has failed to meet its primary endpoint, the drugmaker said Thursday.

A subset of trial patients 18 and older, however, showed statistically significant improvements in lung function and secondary endpoints such as respiratory health, Vertex added.

Based on that result, the company believes Kalydeco (ivacaftor) provides a clinical benefit for this patient group and will meet with the FDA early next year to discuss an sNDA for this indication.

For four percent of the world’s cystic fibrosis patients, Kalydeco is a wonder drug. Approved by the FDA in 2012 for patients ages 6 and older with at least one copy of the G551D mutation, Kalydeco is the first drug to treat the underlying cause of cystic fibrosis: defects in the mechanisms by which salt and water are moved in and out of the cell that cause a thick, sticky mucus to build up in organs such as the lungs and pancreas.

The drug won breakthrough therapy designation in the U.S. in January. Vertex continues to test the drug in two Phase III studies of patients homozygous for F508del, as well as in patients with other residual function mutations. Data from these studies are expected in mid-2014.

Kalydeco is also available in the UK, Australia, Canada and New Zealand. — Lena Freund