Development of a high-performance liquid chromatographic method for the determination of mifepristone in human plasma using norethisterone as an internal standard: application to pharmacokinetic study

ObjectiveThe objective of this study was to develop a simple, sensitive, stable and validated HPLC method for the determination of mifepristone levels in human plasma.MethodsSolid-phase extraction cartridges were used to extract plasma samples. Separation was carried out on a C18 column maintained at 20°C with acetonitrile–water (80:20, v/v) as mobile phase at a flow rate of 0.6 mL/min. Norethisterone was employed as the internal standard. Dual wavelength mode was used, with mifepristone monitored at UV 302 nm and norethisterone at 240 nm.ResultsThe calibration curve was linear in the concentration range of 5–10 000 ng/mL, with linear correlation coefficient r being 0.9999. The limit of detection for the assay was 3 ng/mL. The inter-day accuracy ranged from 92.4% to 98.4% and precision 3.6% to 11.4%. The intra-day accuracy ranged from 92.1% to 100.6% and precision 4.7% to 12.2%. The absolute recovery was 91.7–100.1%. Plasma samples were stable for at least 1 month if stored at −20°C. This validated HPLC method was successfully applied to pharmacokinetic study of mifepristone in human plasma samples collected from volunteers after oral administration of 10 mg mifepristone.ConclusionThe simple, accurate and stable method allows the sensitive determination of mifepristone in human plasma at the nanogram level. It could be applied to assess the plasma level of mifepristone in women up to 5 days after oral administration of 10 mg mifepristone.