A rapid and specific assay, based on liquid chromatography—atmospheric pressure chemical ionization mass spectrometry, for the determination of MK-434 (a 5α-reductase inhibitor) and its metabolites in plasma

MK-434 is a new 5α-reductase inhibitor. A sensitive and specific assay based on combined liquid chromatography—mass spectrometry (LC—MS) has been developed for the determination of this compound in plasma. The analyte was isolated from plasma by solid-phase extraction on a C18 cartridge. A related substance, L-654,066, was used as the internal standard. Extracts were separated on a 5-cm C18-reversed-phase high performance liquid chromatography column interfaced via the heated nebulizer probe to a corona discharge chemical ionization source. The mass spectrometer was operated in the positive ion MS—MS mode. The method had sufficient sensitivity, precision, accuracy, and selectivity for the analysis of clinical samples containing MK-434 and its two principal metabolites at concentrations in the range 0.5–50 ng ml−1. The chromatographic run time was <5 min.