Summary 
         
         This study investigated the safety, pharmacokinetics and pharmacodynamics of multiple
            oral doses of R1663, a factor Xa inhibitor, and explored the influence of age and
            gender on pharmacokinetics and pharmacodynamics of R1663. This was a single-blind,
            randomised, placebo-controlled, dose escalation study in 48 healthy male volunteers
            aged 18 to 44 years. R1663 doses up to 300 mg twice daily or 400 mg once daily were
            administered for seven days. The exploration of gender and age effect was carried
            out in separate cohorts of eight male and eight female volunteers aged 45 to 65 years.
            Multiple oral doses of R1663 were safe and well tolerated. Pharmacokinetics was linear
            and showed moderate variability. Plasma concentrations peaked at 3 hour. Terminal
            half-life at steady state was 3–5 hours. Accumulation of R1663 was minimal. R1663
            prolonged clotting times, inhibited thrombin generation (peak height and endogenous
            thrombin potential [ETP]) and anti-factor Xa activity in a concentration-dependent
            manner without increasing bleeding time. Pharmacodynamic parameters were strongly
            correlated to R1663 plasma concentrations. The inhibition was more pronounced on peak
            height (IC50  = 194 ng/ml) than on ETP (2790 ng/ml). Pharmacokinetics and pharmacodynamics of R1663
            appeared not to be substantially affected by age or gender but remained to be confirmed
            in larger clinical trials including older patients. Meanwhile, dose adjustments based
            on age and gender are not anticipated.
         Keywords Factor Xa inhibitor - multiple ascending dose study - healthy volunteers - gender
            and age effect