Objective: To investigate inhibition of baicalin on activity of cytochrome P450 (CYP450) enzyme in rat and human liver microsomes

and then compare species difference between them.In addition

possibility of drug interaction with baicalin was evaluated. Method: Liver microsomes combine with specific probe substrates were used in vitro and metabolites of substrates were determined by LC-MS/MS.The mass spectrometer was operated with electrospray ionization (ESI) and selective reaction monitoring (SRM) scan mode.Chromatographic separation was performed on a ZORBAX Eclipse-plus C18 column with mobile phase of methanol-water (containing 0.1% formic acid) by gradient elution.Hemi-inhibitory concentration (IC50) was calculated to assess inhibition of baicalin on CYP450. Result: In rat liver microsomes

baicalin showed no inhibition on CYP1A2

CYP2B6

CYP2C9

CYP2C19

CYP2D6

CYP2E1 and CYP3A4.However

in human liver microsomes

CYP1A2

CYP2C19 and CYP2E1 were inhibited weakly by baicalin

IC50 of them were 39.72

40.91

32.83 μmol·L-1. Conclusion: Species difference exists in inhibition of baicalin on CYP450

baicalin is a weak inhibitor for CYP1A2

CYP2C19 and CYP2E1.Drug interaction caused by inhibition of CYP450 enzymes should be paid attention

when baicalin is used intravenously in clinic.