Plasma quantitation of warfarin and warfarin alcohol by gas chromatography chemical ionization mass spectrometry in patients on warfarin maintenance therapy.

A quantitative method has been developed to measure plasma concentrations of warfarin and warfarin alcohol. The analytical procedure uses deuterated analogues as internal standards, and the technique of selected ion monitoring following gas chromatography methane chemical ionization mass spectrometry of the 4'-methyl ethers of warfarin and warfarin alcohol. Concentrations of warfarin and warfarin alcohol have been measured in plasma samples from 43 patients maintained on chronic warfarin therapy and compared with the 'apparent warfarin' concentration as measured by a fluorometric procedure. The study demonstrated a high degree of correlation between the gas chromatography mass spectrometric derived sum of the individual concentrations of warfarin and warfarin alcohol, and the 'apparent warfarin' concentration determined from a spectrofluorometric assay.