EFFECTS OF INDIVIDUAL GINSENOSIDES, GINKGOLIDES AND FLAVONOIDS ON CYP2C19 AND CYP2D6 ACTIVITY IN HUMAN LIVER MICROSOMES

SUMMARY1 The effects of four individual ginsenosides (Rb1, Rb2, Rc and Rd), two ginkgolides (A and B) and one flavonoid (quercetin) on CYP2C19‐dependent S ‐mephenytoin 4¢‐hydroxylation and CYP2D6‐mediated bufuralol 1¢‐hydroxylation were evaluated in human liver microsomes. 2 Increasing concentrations of each test compound were added to microsomal incubation mixtures containing a well‐characterized marker substrate ( S ‐mephenytoin for CYP2C19 or bufuralol for CYP2D6) to determine their IC 50 values (compound concentration yielding 50% inhibition of a marker enzyme activity), which were estimated by graphical inspection. 3 For CYP2C19, the IC 50 values were 46, 46 and 62 mmol/L for ginsenoside Rd, quercetin and ginsenoside Rb2, respectively, whereas only ginsenoside Rd had an IC 50 value of 57 mmol/L for CYP2D6. 4 The data suggest that the tested compounds are not likely to inhibit the metabolism of the concurrent use of a given drug whose primary route of elimination is through CYP2C19 or CYP2D6.