Plasma half-lives, plasma metabolites and anticoagulant efficacies of the enantiomers of warfarin in man

Abstract

S-(-)-Warfarin was found to be a more potent anticoagulant than R-(+)-warfarin in man. However, S-warfarin was cleared more rapidly from the plasma; respective mean plasma half-lives (from four subjects) for R and S-warfarin were 45ṁ4 and 33ṁ0h. Unlike the assay of Lewis, Ilnicki & Carlstrom (1970), the assay of Corn & Berberich (1967) for measuring plasma warfarin gave spuriously long half-life values, particularly with R-warfarin. The apparent volumes of distribution of the enantiomers were not significantly different. A major plasma metabolite detected was warfarin alcohol1, which was seen in much greater quantities after giving R-warfarin than after S-warfarin. The corresponding diastereoisomer, warfarin alcohol2, was seen in trace amounts after S-warfarin only.