Comparison of the pharmacokinetics, pharmacodynamics and tolerability of tezosentan between caucasian and Japanese subjects

Aim To investigate the pharmacokinetics, pharmacodynamics and tolerability of the dual endothelin receptor antagonist tezosentan in caucasian and Japanese subjects. Methods Twelve subjects of each ethnic origin were treated in a double-blind, randomized design with sequential 3-h infusions of 2.5, 5.0, 12.5 and 25 mg h(-1), or placebo. Vital signs, ECG and adverse events were recorded and blood samples collected for determination of plasma concentrations of tezosentan and endothelin-1 (ET-1). Results Tezosentan was well tolerated in both ethnic groups with no clinically significant differences in laboratory measurements, ECG parameters and vital signs. The plasma concentration-time profiles of tezosentan were described by a three-compartment model with half-lives of approximately 5 min, 41 min and 3.6 h. Mean clearance and volume of distribution were approximately 35 l h(-1) and 20 l, respectively. Differences in the means (95% confidence intervals) between ethnic groups in these two parameters were 6.0 l h(-1) (-1.3, 13.3) and 4.3 l (-1.3, 9.9), respectively. Baseline ET-1 concentrations were similar but increases in response to tezosentan were greater in caucasian than in Japanese subjects. An indirect response model described the relationship between tezosentan and ET-1 plasma concentrations. The mean concentrations inhibiting 50% of ET-1 clearance (IC50) in caucasian and Japanese subjects were 243 and 227 ng ml(-1), respectively, with a difference in the means of 28.6 ng ml(-1) (-52.7, 110). Conclusions The data in healthy subjects suggest that caucasian and Japanese patients can be treated with a similar dosing regimen of tezosentan.