The Effects of Elexacaftor, Tezacaftor, and Ivacaftor (ETI) on Blood Glucose in Patients With Cystic Fibrosis: A Systematic Review

Cystic fibrosis (CF) is an autosomal recessive genetic disorder resulting from defects in the cystic fibrosis transmembrane conductance regulator (CFTR) protein, which in turn results in a multi-systemic disorder. There are numerous known CF alleles associated with different mutations of the CFTR gene, with the most common CF allele being a three-base-pair deletion known as Delta F508. One common manifestation of CF is glycemic dysregulation associated with decreased insulin secretion, often progressing into a distinct form of diabetes known as cystic fibrosis-related diabetes (CFRD). In the past decade, a class of drugs known as CFTR modulators has entered clinical practice. These drugs interact with the CFTR protein to restore its function, with different modulators (or combinations of modulators) suitable for patients with different CFTR mutations. Previous research has established that the modulator ivacaftor is effective in decreasing blood glucose and sometimes resolving CFRD in patients with certain CFTR mutations (class III mutations). However, early modulator therapies for individuals with the common Delta F508 mutation (e.g., a combination of the modulators lumacaftor and ivacaftor) have largely proven ineffective in improving glucose regulation. More recently, a combination therapy of three modulators, namely elexacaftor, tezacaftor, and ivacaftor (ETI), has entered clinical practice for patients with the Delta F508 mutation. However, it is not clear whether this therapy is effective in treating dysglycemia. We searched for studies of any design that examined the effects of ETI on measures of blood glucose. All available studies were observational studies comparing patients before and after initiating ETI therapy. Measures of daily-life blood glucose (those obtained with continuous glucose monitoring systems or by measuring glycated hemoglobin (HbA1c)) and post-prandial glucose spikes from oral glucose tolerance tests showed significant improvements in at least some studies. The majority of studies showed significant improvements from pre- to post-ETI in one or more blood glucose measures. While the interpretation of this evidence is complicated by the lack of randomized controlled trials, it appears that ETI therapy is associated with improved glucose regulation for at least some patients with the Delta F508 mutation.