Effects of a combination of sitagliptin plus metformin vs metformin monotherapy on glycemic control, β-cell function and insulin resistance in type 2 diabetic patients

Aims: To evaluate the impact on glycemic control, insulin resistance, and insulin secretion of sitagliptin. +. metformin compared to metformin in type 2 diabetic patients. Methods: Patients were instructed to take metformin for 8 ± 2 months, then they were randomly assigned to sitaglipin 100. mg or placebo for 12 months. We evaluated at 3, 6, 9, and 12 months: body mass index (BMI), glycemic control, fasting plasma insulin (FPI), HOMA-IR, HOMA-β, fasting plasma proinsulin (FPPr), proinsulin/fasting plasma insulin ratio (Pr/FPI ratio), C-peptide, glucagon, adiponectin (ADN), and high sensitivity-C reactive protein (Hs-CRP). Before, and after 12 months since the addition of sitagliptin, patients underwent a combined euglycemic hyperinsulinemic and hyperglycemic clamp, with subsequent arginine stimulation. Results: Both treatments similarly decreased body weight, and BMI; on the other hand, they both improved glycemic control, glucagon and HOMA-IR, but sitagliptin. +. metformin were more effective in reducing these parameters. Sitagliptin. +. metformin, but not placebo. +. metformin, decreased FPPr, FPPR/FPI ratio, and increased C-peptide values, even if no differences between the groups were recorded. Sitaglitin. +. metformin gave also a greater increase of HOMA-β, M value, C-peptide response to arginine and disposition index compared to placebo. +. metformin group. Conclusions: Other than improving glycemic control, sitagliptin. +. metformin also improved β-cell function better than metformin alone.