Ivacaftor. Uncertain harm-benefit balance

Cystic fibrosis is a serious genetic disease due to mutations in the gene encoding CFTR (Cystic FibrosisTransmembrane conductance Regulator), a protein involved in cellular transmembrane transport, particularly of chloride ions. Ivacaftor is described as a selective potentiator of CFTR protein. It is now licensed for the treatment of cystic fibrosis patients 6 years of age and older who carry the CFTR G551D mutation, which is the case for about 4% to 5% of cystic fibrosis patients. Two randomised placebo-controlled trials of ivacaftor have been carried out in this setting, in a total of 213 patients. The frequency of pulmonary exacerbations fell in one of the two trials during the first 48 weeks of treatment, but there was no impact on the number of hospitalisations or the use of intravenous antibiotics. In both trials, addition of ivacaftor improved FEV1 by an average of about 10% at week 24 and increased body weight by an average of about 2.5 kg after 1 year. Upper respiratory tract infections occurred in the ivacaftor groups during these trials, with more cases of bacterial contamination and, possibly, more pulmonary exacerbations in the longer term. Ivacaftorcarries a risk of numerous pharmacokinetic interactions that can require dose adjustment, particularly for patients with hepatic impairment and those receiving cytochrome P450 isozyme 3A inhibitors or inducers. Given the absence of data, ivacaftor should be avoided during pregnancy. In practice, in 2013, it is not possible to determine the harm-benefit balance of ivacaftor due to the high risk of drug interactions, as well as a possible increased risk of infections and liver toxicity.