Evaluation of add-on therapy of sitagliptin in Japanese patients with type 2 diabetes under insulin therapy

Objective To examine the impact of add-on sitagliptin therapy on glucose, endogenous insulin and glucagon concentrations in Japanese patients with type 2 diabetes under insulin therapy. Research design and methods Sixty-two patients (mean age 59.0 years) undergoing insulin therapy were treated with add-on sitagliptin, and various parameters including HbA 1c were compared before and 4 months after sitagliptin administration by the paired t -test. Multivariate analysis was performed to further identify factors independently associated with some outcomes of the therapy, including the reduction of HbA 1c and the desirable outcome (reduction of HbA 1c without increase in BW). Results There were significant decreases in mean HbA 1c (8.6–7.7 %), mean PG at 60 min and 120 min in the meal tolerance test (MTT) (242–212 and 228–196 mg/dL) ( p < 0.005), significant increases in mean C-peptide reactivity (CPR) at 0 and 60 min in the MTT (1.00–1.14 and 1.63–1.78 ng/mL) ( p < 0.05), and significant decreases in mean glucagon at 60 and 120 min in the MTT (88.2–81.5 and 85.4–78.8 pg/mL) ( p < 0.05). There was neither a significant change in mean BW nor serious adverse events including episodes of severe hypoglycemia. Multivariate regression analysis showed that baseline HbA 1c was the only factor related to the change in HbA 1c by sitagliptin add-on therapy. Multiple logistic regression analysis revealed that a bolus insulin dose of ≥15 units/day was significantly associated with the desirable outcome. Conclusions Add-on sitagliptin therapy may be a new therapeutic option in patients with type 2 diabetes who have inadequate glycemic control with insulin therapy, possibly using a bolus insulin dose of ≥15 units/day.