A stable isotope assay for pseudoracemic warfarin from human plasma samples.

A pseudoracemic technique utilizing a seable isotope in one enantiomer was employed for the simultaneous determination of (R) and (S)-warfarin from plasma of human subjects. The assay includes high performance liquid chromatographic clean-up prior to mass spectral analysis to eliminate ion interferences from either co-administered drugs or contamination of the source. The assay is reliable, accurate and precise to within 5% at the submicrogram level.