A sensitive and specific stable isotope assay for warfarin and its metabolites

A capillary gas chromatographic mass spectrometric method for the quantification of warfarin and its known metabolites from microsomal incubations is described. Deuterium labelled 4', 6-, 7- and 8-hydroxy warfarins are used as internal standards and the method has detection limits of 1 ng ml-1 with 20 ng ml-1 being the lower limit for accurate quantification.