Pharmacokinetics and Pharmacodynamics of Oral Tolvaptan Administered in 15- to 60-mg Single Doses To Healthy Korean Men

Abstract

Tolvaptan is a selective arginine vasopressin V2-receptor antagonist that is used as an aquaretic agent. This trial investigated the pharmacokinetics and pharmacodynamics of 15- to 60-mg single oral doses of tolvaptan in healthy Korean men. A dose block-randomized, placebo-controlled, double-blind, single ascending dose trial was conducted with 46 subjects receiving tolvaptan (15, 30, or 60 mg) or placebo. To determine pharmacokinetics and pharmacodynamics, blood and urine samples were collected at baseline and up to 48 hours after drug administration. Urine volume and fluid intake were measured for 24 hours starting the day before dosing (day -1) as baseline, and on the day of drug administration (day 1). Tolvaptan showed dose-linear pharmacokinetic characteristics regarding area under the concentration-time curve. Changes from baseline in 24-hour urine volume and 24-hour fluid balance correlated significantly with area under the concentration-time curve from time 0 to the last measurable time. Dose-dependent increases were observed in serum osmolality, serum sodium concentration, and free water clearance in the 4- to 8-hour interval after dosing, and these increases were maintained for at least 24 hours. Single 15- to 60-mg doses of tolvaptan exhibited linear pharmacokinetics and resulted in substantial, dose-dependent aquaresis in healthy Korean men.