Vildagliptin is a potent and selective dipeptidyl peptidase-IV (DPP-4) inhibitor that improves glycemic control in patients with type 2 diabetes mellitus by increasing α- and β-cell responsiveness to glucose. This study investigated the pharmacokinetics of vildagliptin in patients with hepatic impairment compared with healthy subjects. This was an open-label, parallel-group study in patients with mild ( n = 6), moderate ( n = 6) or severe ( n = 4) hepatic impairment and healthy subjects ( n = 6). All subjects received a single 100-mg oral dose of vildagliptin, and plasma concentrations of vildagliptin and its main pharmacologically inactive metabolite LAY151 were measured up to 36 h post-dose. Exposure to vildagliptin (AUC0–∞ and Cmax) decreased non-significantly by 20 and 30%, respectively, in patients with mild hepatic impairment [geometric mean ratio (90% CI): AUC0–∞, 0.80 (0.60, 1.06), p = 0.192; Cmax, 0.70 (0.46, 1.05), p = 0.149]. Exposure to vildagliptin was also decreased non-significantly in patients with moderate hepatic impairment [−8% for AUC0–∞, geometric mean ratio (90% CI): 0.92 (0.69, 1.23), p = 0.630; −23% for Cmax, geometric mean ratio (90% CI): 0.77 (0.51, 1.17), p = 0.293]. In patients with severe hepatic impairment, Cmax was 6% lower than that in healthy subjects [geometric mean ratio (90% CI): 0.94 (0.59, 1.49), p = 0.285], whereas AUC0–∞ was increased by 22% [geometric mean ratio (90% CI): 1.22 (0.89, 1.68), p = 0.816). Across the hepatic impairment groups, LAY151 AUC0–∞ and Cmax were increased by 29–84% and 24–63%, respectively, compared with healthy subjects. The single 100-mg oral dose of vildagliptin was well tolerated by patients with hepatic impairment. There was no significant difference in exposure to vildagliptin in patients with mild, moderate or severe hepatic impairment; therefore, no dose adjustment of vildagliptin is necessary in patients with hepatic impairment. [ABSTRACT FROM AUTHOR]