The absolute oral bioavailability and population-based pharmacokinetic modelling of a novel dipeptidylpeptidase-IV inhibitor, vildagliptin, in healthy volunteers

Background and objective: Vildagliptin is a potent, selective, orally active inhibitor of dipeptidylpeptidase-TV being developed for the treatment of type 2 diabetes mellitus. The objective of this study was to assess the absolute oral bioavailability of vildagliptin by comparing the systemic exposure after oral and intravenous administration in healthy volunteers. Methods: This was an open-label, randomised, two-period, two-treatment, crossover study in 11 healthy volunteers. Subjects received vildagliptin 50mg orally or 25mg as a 30-minute intravenous infusion on two occasions separated by a 72-hour washout period. Vildagliptin concentrations were determined by a specific assay in urine (lower limit of quantification [LLQ] = 5 ng/mL) and serial plasma samples (LLQ = 2 ng/mL) obtained up to 24 hours after dosing. Noncompartmental analysis and population pharmacokinetic modelling were performed. Results: Both noncompartmental analysis and population pharmacokinetic modelling estimated the absolute oral bioavailability of vildagliptin to be 85%. Renal elimination of unchanged vildagliptin accounted for 33% and 21 % of the administered dose 24 hours after intravenous and oral administration, respectively. Renal clearance (13 L/h) was approximately one-third of the total systemic clearance (41 L/h). Two peaks were observed in plasma concentrations at I and 3 hours after oral administration in nine of I I subjects. Modelling based on the population approach identified two absorption sites with lag-times of 0.225 and 2.46 hours. Both absorption rate constants were slower than the elimination rate constant, indicating 'flip-flop' kinetics after oral administration. Bodyweight was identified as a factor with an impact on the volume of distribution of the peripheral compartment. Clearance was 24% greater in males (44.6 L/h) than in females (36.1 L/h). Conclusions: Vildagliptin is rapidly and well absorbed with an estimated absolute bioavailability of 85%. Two possible sites of absorption were identified, and the absorption rates were slower than the elimination rate, indicating a flip-flop phenomenon after oral dosing.