Tezacaftor and ivacaftor for the treatment of cystic fibrosis.

: Cystic fibrosis (CF) is a complex, multi-system, genetic disease affecting over 70,000 people worldwide. The underlying defect is a mutation in the CFTR gene. Dysfunctional CFTR protein results in abnormal anion movement across epithelial membranes in affected organs.

Sweat chloride is not a useful marker of clinical response to Ivacaftor.

Clinical trials have revealed that Ivacaftor significantly reduces sweat chloride in patients with cystic fibrosis who carry the G551D mutation. This finding has been incorporated into the commissioning guidelines in the UK with a sweat chloride reduction of 30% or below 60 mmol/L, specified as the main criteria for continued funding of Ivacaftor for individual patients. In a cohort of 24 adults who were prescribed Ivacaftor, there was no correlation between absolute or relative reductions in sweat chloride and improvements in lung function.