Improved detectability in pharmacokinetic study of tibolone by gas chromatography-high resolution mass spectrometry with selected ion monitoring.

A combination of high resolution mass spectrometry (HRMS) and gas chromatography has been used to improve sensitivity and selectivity in pharmacokinetic study of tibolone. The study was undertaken in 12 healthy volunteers after oral administration of 2.5mg tibolone tablet and plasma concentrations of two major metabolites, 3alpha-hydroxytibolone (3alphaOHT) and 3beta-hydroxytibolone (3betaOHT), were analyzed first by gas chromatography-mass spectrometry (GC-MS). Pharmacokinetic parameters AUC(0-12h) (13.70+/-4.01nghml(-1)), C(max) (3.89+/-1.00ngml(-1)), and T(max) (1.83+/-0.55h) for 3alphaOHT were initially measured by GC-MS. The AUC(0-12h) of 3betaOHT concentration was 5.5-folds higher than that of 3alphaOHT. Improved results in detectability were obtained by GC-HRMS analysis of two metabolites with the same samples. The previously undetected metabolites, 3alphaOHT and 3betaOHT, in samples collected at 15 and 24h in GC-MS system were successfully detected by GC-HRMS analysis and could be calculated pharmacokinetic parameters as well. But, no significant pharmacokinetic parameters were found in two analytical runs. The limit of quantification for HRMS analysis in selected ion monitoring mode of 3alphaOHT and 3betaOHT as trimethylsilyl derivatives down to 0.02ngml(-1), while their recovery rates varied in the range of 82.5-108.0%. This method demonstrated a good overall accuracy and precision as 90.1-102.3% and 1.6-11.4%, respectively. This method could potentially have implications for pharmacokinetic study or clinical trial of rapidly metabolized drugs.