Use of Vertex Pharmaceuticals’ cystic fibrosis drug Kalydeco has been expanded in the US to include some children under the age of two.

The US Food and Drug Administration is allowing the drug’s use in those aged under 24 months who carry at least one mutation in their cystic fibrosis transmembrane conductance regulator (CFTR) gene.

The approval came on the back of data from the ongoing Phase III open-label safety study (ARRIVAL) of 25 children with CF aged 12 to <24 months who have one of 10 mutations in the CFTR gene (G551D, G178R, S549N, S549R, G551S, G1244E, S1251N, S1255P, G1349D or R117H).

According to Vertex, the study showed a safety profile consistent with that observed in previous Phase III studies of older children and adults; “most adverse events were mild or moderate in severity, and no patient discontinued due to adverse events”.

Two patients had elevated liver enzymes greater than eight times the upper limit of normal, but continued to receive Kalydeco (ivacaftor) after a dose interruption, while the most common adverse events were cough (74 percent), pyrexia (37 percent), elevated aspartate aminotransferase (37 percent), elevated alanine aminotransferase (32 percent) and runny nose (32 percent). Four serious adverse events were observed in two patients.

Also, in the 10 subjects with paired sweat chloride samples (the concentration of chloride in sweat is elevated in individuals with CF) at baseline and week 24, there was a mean absolute change of -73.5 mmol/L.

“I’m very excited about the approval of ivacaftor in children ages 12 to less than 24 months as this is the first regulatory approval of a CFTR modulator in this age group,” said Margaret Rosenfeld, Seattle Children’s Research Institute and Department of Pediatrics, University of Washington School of Medicine.

“The premise of newborn screening for CF is to intervene very early in the course of disease with the goal of improving long term outcomes, so this is a significant milestone for parents and caregivers of young children with CF.”

CF is a rare, life-shortening genetic disease affecting approximately 75,000 people in North America, Europe and Australia.

Kalydeco is already approved for the treatment of CF in patients ages two and older who have one of 38 ivacaftor-responsive mutations in the CFTR; an application to expand the drug’s scope to include children aged under two is also currently under review in Europe, with a decision expected in the first half of next year.