Simultaneous determination of urinary free cortisol and 6beta-hydroxycortisol by liquid chromatography-atmospheric pressure chemical ionization tandem mass spectrometry and its application for estimating hepatic CYP3A induction.

A reversed-phase high-performance liquid chromatography coupled to atmospheric pressure chemical ionization tandem mass spectrometry (HPLC-APCI-MS-MS) assay was developed to simultaneously determine monkey urinary free cortisol (C) and 6beta-hydroxycortisol (6beta-OHC) in 8 min. Urine sample (0.5 ml) containing fludrocortisone acetate (F-C) as the internal standard was extracted with ethyl acetate for 5 min with an extraction efficiency of 90% and 75% for C and 6beta-OHC, respectively. A Perkin-Elmer Sciex API 3000 triple quadruple instrument was used for mass spectrometric detection and the column eluent was directed to a heated nebulizer probe. The assay was linear over the range 0.25-10 microM for each analyte. The intra- and inter-day relative standard deviation (RSD) over the entire concentration range for both analytes was less than 10%. Accuracy determined at three concentrations (0.8, 2.0 and 8.0 microM) ranged between 95.5 and 108%. The method described herein is suitable for the rapid and efficient measurement of 6beta-OHC/C ratio in Rhesus monkey urine following administration of known hepatic CYP3A inducers and can be used to estimate potential CYP3A induction by drug candidates in the process of early drug development.