In vitro assessment of plasma protein binding of 20(R)-ginsenoside Rh2 by equilibrium dialysis and LC-MS analysis: A case of species differences

20(R)-Ginsenoside Rh2 is isolated from Chinese traditional ginsengs with main antitumor effects. To support its pharmacokinetic study which was essential for the pre-clinical research for new drug development, in this paper, 20(R)-Rh2 plasma protein binding was assessed in vitro at four concentration levels (50, 100, 200, 400 ng/ml) both in rat and human plasma using equilibrium dialysis and followed by LC-MS analysis. The method was optimized against some influencing factors during both experimental procedures. And it was validated to be specific, sensitive, accurate, precise and of satisfactory recovery. The results showed the binding fractions were about 70% for rats and 27% for human within four concentration levels. It exhibited a significant species difference between human and rats for the plasma protein binding of 20(R)-Rh2.