Objective: To investigate the influence of daily administration frequency of rhubarb on the antioxidant effect in vitro and to determine the rational frequency for rhubarb application. Method: Rhubarb extract was administrated to Wistar rats(G1

G2 and G3 group)in a dose of 3.6 g·kg-1 once a day

1.8 g·kg-1 twice a day

1.2 g·kg-1 three times a day

respectively. Blood sample was collected from orbital venous before the administration (0 h) and after the administration of 0.083

0.167

0.25

0.5

1

2

4

6

8

10

12

24 h. Blood sample was used for the experiments of antioxidant in vitro

such as scavenging effect of superoxide anion radical

diphenyl-generation bitterness acyl radical and hydroxyl radicals. And then antioxidant effect-time curve was obtained by fitting its compartment model and calculating parameters. Result: There was good correlation between daily administration frequency and antioxidant effects of rhubarb. Area under the curve of E-T (AUCE) of administration twice daily was significantly higher than those of administrated 1 or 3 times daily (P<0.05). Conclusion: It is more appropriate to administrate rhubarb twice daily when it is used as antioxidant.