Reply to the comment of Wilbrink et al. on Retrospective analysis of liraglutide and basal insulin combination therapy in Japanese type 2 diabetes: The association between remaining β-cell function and the achievement of the HbA1c target 1 year after initiation.

We have reported that the HbA1c-lowering effects of liraglutide/basal insulin combination rely on remaining β-cell function and that the cut-off value of the C-peptide immunoreactivity index (CPI), a β-cell function-related index frequently used in Japanese clinical settings, is 1.103 for the achievement of HbA1c <7.0% at 54 weeks after initiating the liraglutide/basal insulin combination. Wilbrink et al claimed that glucose-lowering effects of glucagon-like peptide-1 receptor agonist liraglutide depend of duration of type 2 diabetes; while our resent study published in the Journal of Diabetes Investigation failed to detect such dependency. This discrepancy might be due to several reasons including co-administration of basal insulin with liraglutide in our study; ethnic difference in T2D pathophysiology between the two study; and difference in sample size (The Usui study on liraglutide/basal insulin, n = 38; the Usui study on liraglutide monotherapy or SU combination, n=88; and the Wilbrink study, n = 69).