Ivacaftor, also known as VX-770, is a drug used to treat cystic fibrosis in people with certain mutations in the cystic fibrosis transmembrane conductance regulator (CFTR) gene, who account for 4–5% cases of cystic fibrosis, and is included in a combination drug, lumacaftor/ivacaftor, which is used to treat people with cystic fibrosis who have the F508del mutation in CFTR. Ivacaftor is a "potentiator" of CFTR, meaning it increases the probability that the defective channel will be open and allow chloride ions pass through the channel pore.