Several studies have shown that FPG variability is associated with diabetic complications, severe hypoglycemia, or death [
7,
8], suggesting that stabilization of FPG should be a therapeutic target for individuals with diabetes. Moreover, administered basal insulin can greatly influence FPG variability, especially in C-peptide-negative individuals with type 1 diabetes treated with basal-bolus insulin injection. We previously compared IDeg and IGlar U100 with regard to their effects on FPG variability in such patients and found that IDeg yielded a lower FPG level and smaller day-to-day variability in FPG at a lower daily dose compared with IGlar U100 [
12]. The longer and more stable action of IDeg is due both to its slower absorption from the injection site into the circulation as a result of its formation of soluble multihexameric chains and to its prolonged retention in the circulation as a result of its binding to albumin in blood [
13]. On the other hand, IGlar U300 is a newly developed ultra-long-acting basal insulin that is superior to IGlar U100 in terms of its longer action and more even effect [
3,
4]. As a result of its threefold more concentrated formulation, the microprecipitates of subcutaneously injected IGlar U300 have a longer residence time at physiological pH compared with IGlar U100 [
3]. Although both IDeg and IGlar U300 are now available in clinical practice, differences in the effects of these ultra-long-acting basal insulins have not been established. The results of euglycemic glucose clamp studies to compare the stability of the glucose-lowering effects of injected IDeg and IGlar U300 have not been consistent [
14‐
16]. Recently, the efficacy and safety of IDeg and IGlar U300 were compared in a head-to-head randomized controlled clinical trial in type 2 diabetes (BRIGHT Trial) [
17]. The trial revealed that the two basal insulins have similar effects on HbA
1c improvement (in primary outcome), and less occurrence of hypoglycemia in IGlar U300 than in IDeg (in secondary outcome) if target FPG level was set as 80–100 mg/dl. The information on the difference of fasting glycemic variability has still not been reported to date.
The current study is the first randomized controlled trial to directly compare the two ultra-long-acting basal insulins with regard to their effects on day-to-day glycemic variability in C-peptide-negative patients with type 1 diabetes. The results of our study should prove informative for selection of the best basal insulin for the treatment of type 1 diabetes in the clinical setting.