Pharmacokinetic Study of Midazolam-A Cytochrome P450 3A Activity Probe / 中药新药与临床药理

ABSTRACT

Objective To develop a high performance liquid chromatography-ultraviolet detection(HPLC-UV) method for the determination of midazolam in rat plasma,and to study the pharmacokinetics of midazolam in single dose intravascular administration in rats.These results can provide a methodological reference for evaluating cytochrome P450 3A(CYP3A) activity.Methods Firstly,common carotid artery(CCA) intubate was set in rats,Midazolam was injected into rat vena caudalis and plasma samples were collected in different time.Then,the sample was extracted using dichlormethane and evaporated to dry thoroughly with N2 soft stream at 37 ℃.Finally,the residues were reconstituted with 150 ?L 30 %methanol and further analyzed by HPLC.A Phenomenex C18 column(4.6?150 mm i.d,5 ?m)was employed at 20 ℃.The mobile phase consisted of(A) methanol-acetonitrile-0.03 %phosphate solution(pH 2.85) in the proportion of 51085(V/V/V) and(B) methanol-acetonitrile-0.03 %phosphate solution(pH 2.85) in the proportion of 51085(V/V/V),using a linear gradient elution of 0 %B～100 %B at 0～18 minutes,then retaining for 5 minutes and returning to A.The flow rate was set at 0.5 mL/min and the ultraviolet detector was operated at 240 nm.Results Midazolam and internal standard were isolated on baseline in plasma apart from all other material.The the linear range was from 0.025～2.0 ?g/mL,and the detection limit was 2.5 ng/mL.The standard addition recoveries were from 99.98 %to 105.71 %and the extraction rates were from 91.29 %to 92.58 %.All of the intraday and interday variations were less then 14 %.The primary pharmacokinetics parameters of rat single dose intravascular administration were as followst1/2?was 0.582 h,Vd was 0.214 L,Cl was 0.584 L/h and AUC0→t was 0.419 ?g?h-1?mL-1.Conclusion Midazolam single dose intravascular administration has the characteristics of rapid distribution and elimination in blood and quick transport from blood to tissue.The method is sensitive,simple and suitable for the research of pharmacokinetie parameters of midazolam and description of possible pharmacological interactions of rat CYP3A1/2 or human CYP3A4/5 enzymes.