Aim/IntroductionInsulin glargine U100/lixisenatide and insulin degludec/liraglutide are fixed‐ratio combinations containing basal insulin and a glucagon‐like peptide‐1 receptor agonist capable of reducing both fasting and postprandial blood glucose levels with a single formulation. This study aimed to compare the time in range (TIR) and the time below range (TBR) level 1 using professional continuous glucose monitoring and to establish criteria for the differential use of the fixed‐ratio combinations.Materials and MethodsThirty‐six outpatients with type 2 diabetes mellitus (24 men and 12 women; average age, 62.1 years) were randomly assigned to the groups. At 0 and 18 weeks, a device was worn to compare the TIR and TBR level 1. The correlation between the C‐peptide index at baseline and TIR at 18 weeks was assessed.ResultsThe TIR and TBR level 1 showed no significant differences between the two groups. Both groups showed significant positive correlations between the C‐peptide index and the TIR (P = 0.002, r = 0.679; P = 0.002, r = 0.681, respectively). The changes in glycemic variability, therapeutic indices, and body mass index were not significantly different among the groups (P > 0.05). The receiver operating curve analysis revealed that the cut‐off values of the C‐peptide index to achieve TIR of >70% at 18 weeks were 1.258 (sensitivity, 77.8%; specificity, 100%) and 1.099 (sensitivity, 57.1%; specificity, 90.9%) in the insulin glargine U100/lixisenatide and insulin degludec/liraglutide groups, respectively.ConclusionsA TIR of >70% was achieved for both fixed‐ratio combinations without significant differences.