Objective:To establish a rapid and accurate method with omeprazole（OPZ） as a ’probe drug’ in order to evaluate or determine the activity of cytochrome（CYP2C19） by the high-performance liquid chromatography（HPLC）-UV detection（VWD）.Method: The analytical column was used in accordance with Agilent Extend-C18 column（4.6 mm ×100 mm

5 μm）

flow rate at 1.0 mL · min-1

UV detection at 290 nm

and column temperature at 40 ℃.In vivo study: 20 mg · kg-1 of OPZ was given to the rats via the tail vein.Blood samples were collected at designed time points post dose and plasma samples were obtained.OPZ and 5′-hydroxy omeprazole（5′-OHOPZ） were determined by an HPLC method.In vitro study:After incubation

the formation rate of 5′-OHOPZ was used to evaluate the function of CYP2C19.Result: In vivo: the internal standard

OPZ and 5′-OHOPZ retention times were 8.91

10.26

14.93 min.The linear range of OPZ was 0.28-18.0 mg · L-1

and the lower limit of quantitation（LLOQ） was 0.28 mg · L-1.Extraction recovery at low

medium and high concentrations were 91.13%

97.21% and 96.55%

respectively.The intra-and inter-day relative standard deviation（RSD） was less than 10%.The linear range of 5′-OHOPZ was 0.19-6.25 mg · L-1

and the lower limit of quantitation（LLOQ） was 0.19 mg · L-1.Extraction recovery at low

medium and high concentrations were 94.36%

97.57% and 90.64%

respectively.The intra-and inter-day relative standard deviation（RSD） was less than 10%.In vitro: The internal standard

OPZ and 5′-OHOPZ retention times were 8.91

10.26

14.93 min.The linear range of 5′-OHOPZ was 0.06-2.0 mg · L-1

and the lower limit of quantitation（LLOQ） was 0.06 mg · L-1.Extraction recovery at low

medium and high concentrations were 96.53%

99.40% and 98.00%

respectively.The intra-and inter-day relative standard deviation（RSD） was less than 10%.Conclusion: Other endogenous substances in the plasma and incubation system do not interfere with the determination.The method is rapid

stable and highly sensitive.It is suitable for determination of OPZ and its metabolites 5′-OHOPZ and can be used for in vivo and in vitro determination of CYP2C19 activity and research of enzyme kinetics.