Objective      To establish a method for evaluating the activity of cytochrome P450 2C9 (CYP2C9) using diclofenac as the probe compound in rat liver microsomes (RLMs) in vitro

and to investigate the impact of 20 active ingredients of traditional Chinese herbs on CYP2C9 activity.       Methods      Diclofenac and 20 active ingredients of traditi

onal Chinese herbs were incubated with RLMs for 15 min at 37 ℃

and the reaction was terminated by cold acetonitrile. The conversion ratio of 4′-hydroxydiclofenac was determined by HPLC. Finally

the effects of the 20 active ingredients of traditional Chinese herbs on CYP2C9 activities were evaluated by comparison of the conversion ratio with control group.       Results      4′-hydroxydiclofenac

diclofenac and coumarin were perfectly separated. After diclofenac incubation with 0.25 mg/mL RLM for 15 min

the kinetic parameters were revealed

V

max

0.145 6 nmol/(min·mg) and K

m

8.270 μmol/L. Among the 20 active ingredients

baicalein

cnidiadin

emodin

swertiamarin

icariin

and resveratrol displayed strong inhibition on CYP2C9 with the conversion ratio of 402.60±10.58

210.90±10.26

414.46±10.32

509.83±26.45

355.44±15.87

and 387.34±22.16 pmol/(min·mg)

respectively

which were significantly lower than that of control group 735.80±17.27 pmol/(min·mg) (P0.05).       Conclusion      The method for evaluating influences of active ingredients of traditional Chinese herbs on CYP2C9 activity in RLMs in vitro is successfully established. Baicalein

cnidiadin

emodin

swertiamarin

icariin

and resveratrol inhibit CYP2C9 activity in vitro

indicating that we should pay attention to drug-drug interactions of these active ingredients when they are used concomitantly with other drugs in clinical practice.