An accurate and sensitive LC-MS/MS method for determining thalidomide, 5-hydroxy thalidomide and 5'-hydroxy thalidomide in human plasma was developed and validated using umbelliferone as an internal standard. The analytes were extracted from plasma (100 μL) by liquid-liquid extraction with ethyl acetate and then separated on a BETASIL C18 column (4.6 × 150 mm, 5 μm) with mobile phase composed of methanol-water containing 0.1% formic acid (70:30, v/v) in isocratic mode at a flow rate of 0.5 mL/min. The detection was performed using an API triple quadrupole mass spectrometer in atmospheric pressure chemical ionization mode. The precursor-to-product ion transitions m/z 259.1 → 186.1 for thalidomide, m/z 273.2 → 161.3 for 5-hydroxy thalidomide, m/z 273.2 → 146.1 for 5'-hydroxy thalidomide and m/z 163.1 → 107.1 for umbelliferone (internal standard, IS) were used for quantification. The calibration curves were obtained in the concentrations of 10.0-2000.0 ng/mL for thalidomide, 0.2-50.0 ng/mL for 5-hydroxy thalidomide and 1.0-200.0 ng/mL for 5'-hydroxy thalidomide. The method was validated with respect to linear, within- and between-batch precision and accuracy, extraction recovery, matrix effect and stability. Then it was successfully applied to estimate the concentration of thalidomide, 5-hydroxy thalidomide and 5'-hydroxy thalidomide in plasma samples collected from Crohn's disease patients after a single oral administration of thalidomide 100 mg.
Keywords: LC-MS/MS; metabolites; pharmacokinetics; thalidomide.
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