Selective and rapid liquid chromatography-tandem mass spectrometry assay of dutasteride in human plasma

A simple, rapid, sensitive and specific liquid chromatography-tandem mass spectrometry method was developed and validated for quantification of dutasteride (I), a potent and the first specific dual inhibitor of 5alpha-reductase, in human plasma. The analyte and internal standard (finasteride (II)) were extracted by liquid-liquid extraction with diethyl ether/dichloromethane (70/30, v/v) using a Glas-Col Multi-Pulse Vortexer. The chromatographic separation was performed on a reverse phase Xterra MS C18 column with a mobile phase of 10 mM ammonium formate/acetonitrile (15/85, v/v, pH adjusted to 3.0 with formic acid). The protonated analyte was quantitated in positive ionization by multiple reaction monitoring with a mass spectrometer. The mass transitions m/z 529.5 --> 461.5 and m/z 373.3 --> 317.4 were used to measure I and II, respectively. The assay exhibited a linear dynamic range of 0.1-25.0 ng/mL for dutasteride in human plasma. The lower limit of quantitation was 100 pg/mL with a relative standard deviation of less than 15%. Acceptable precision and accuracy were obtained for concentrations over the standard curve ranges. A run time of 1.2 min for each sample made it possible to analyze a throughput of more than 400 human plasma samples/day. The validated method has been successfully used to analyze human plasma samples for application in pharmacokinetic, bioavailability or bioequivalence studies.