Rapid and simultaneous measurement of midazolam, 1'-hydroxymidazolam and digoxin by liquid chromatography/tandem mass spectrometry: application to an in vivo study to simultaneously measure P-glycoprotein and cytochrome P450 3A activity.

Author(s): Xue X, Huang M, Xiao H, Qin X, Huang L, Zhong G, Bi H

Affiliation(s): School of Pharmaceutical Sciences, Sun Yat-sen University, Guangzhou 510006, People's Republic of China.

Publication date & source: 2011-04-28, J Pharm Biomed Anal., 55(1):187-93. Epub 2011 Jan 22.

Publication type: Research Support, Non-U.S. Gov't; Validation Studies

In order to simultaneously determine in vivo P-glycoprotein (P-gp) and Cytochrome P450 3A (CYP3A) activity, a new, rapid and sensitive liquid chromatography/tandem mass spectrometry (LC-MS/MS) method has been developed and fully validated to simultaneously determine midazolam (MDZ, as CYP3A substrate), 1'-hydroxymidazolam (1'-OHMDZ) and digoxin (DG, as P-gp substrate) in rat plasma using digitoxin as the internal standard (IS). After a single step liquid-liquid extraction with tert-butyl methyl ether/dichloromethane (75:25, v/v), analytes were subjected to LC-MS/MS analysis using positive electro-spray ionization (ESI(+)) under selected reaction monitoring mode (SRM). Chromatographic separation was performed on an XTerra MS C18 column (50mmx2.1mm, i.d. 3.5mum). The MS/MS detection was conducted by monitoring the fragmentation of 326.05 --> 244.00 (m/z) for MDZ, 342.02 -->168.01 (m/z) for 1'-OHMDZ, 798.33 --> 651.36(m/z) for DG and 782.67 --> 635.24 (m/z) for IS. The method had a chromatographic running time of 3min and linear calibration curves over the concentrations of 2-400ng/mL for MDZ and 1'-OHMDZ and 0.5-100ng/mL for DG. The recoveries of the method were 86.8-96.3% for MDZ, 84.6-86.4% for 1'-OH MDZ, and 81.7-85.1% for DG. The lower limit of quantification (LLOQ) of the method was 2ng/mL for MDZ and 1'-OHMDZ and 0.5ng/mL for DG. The intra- and inter-batch precision were less than 15% for all quality control samples at concentrations of 5, 50 and 320ng/mL for MDZ and 1'-OHMDZ and 1, 10 and 80ng/mL for DG. The validated LC-MS/MS method has been successfully used to analyze the concentrations of MDZ, 1'-OH MDZ and DG in rat plasma for simultaneous measurement of in vivo P-gp and CYP 3A activity. Copyright (c) 2011 Elsevier B.V. All rights reserved.