Multicenter, Open-Label, 2-Arm, Pilot Trial for Safe Reduction of Basal Insulin Dose Combined with SGLT2 Inhibitor in Type 1 Diabetes Mellitus: Study Protocol for a RISING-STAR Trial

Background: The safe method of instructing insulin dose reduction in combination with SGLT2 inhibitors, dapagliflozin for patients with type 1 diabetes mellitus has not been clarified. In this study, we conducted a stratified, 2-arm, parallel comparative study with the primary endpoint of decreasing the frequency of hypoglycemia by instructing basal insulin dose reduction. Methods: The study has a multicenter, open-label, 2-arm design; 60 type 1 diabetes mellitus patients are being recruited from 7 hospitals. Study subjects have been stratified into 2 groups based on the ratio of basal insulin daily dose (Basal) to total daily insulin dose (TDD). The subjects whose Basal/TDD ratio is <0.4 are instructed not to reduce Basal but to reduce bolus insulin dose by 10% (group A), and subjects with a Basal/TDD ratio >0.4 will be instructed to reduce Basal by 10% (group B). The primary outcome is the daily frequency of hypoglycemia during the intervention period (SGLT2 inhibitor administration), as determined by self-monitoring of blood glucose. We aimed to confirm a greater reduction in frequency of hypoglycemia in group B (reduced Basal), than in group A (non-reduction of Basal and reduced insulin effect levels by 10%). Baseline hypoglycemia was set at 7 +/- 6 times/month. The minimum sample size required to achieve a significance of .05 for a 1-sided t-test with a statistical power at 80% is determined. When the sample size is 26 patients in 1 group, the percentage increase in hypoglycemia exceeds 60%, and the sample size is considered sufficient. Discussion: In this pilot study, we assumed that, given a sufficient Basal, hypoglycemia would be more frequent in patients with type 1 diabetes when combined with SGLT2 inhibitors, provided the Basal was not reduced.