WARFARIN ENANTIOMER DISPOSITION - DETERMINATION BY STEREOSELECTIVE RADIOIMMUNOASSAY

Abstract

Immunoassay techniques offer promise for the selective analysis of enantiomeric substances without prior separation. In a demonstration of this selective analysis, radioimmunoassays were developed for R- and S-warfarin [anti-coagulant; WF]. The 4''-carboxyethyl analog of R,S-WF was resolved and the enantiomeric acids were coupled to bovine serum albumin. Immunization of rabbits with the conjugates led to formation of antisera which selectively bound the predicted enantiomer. Cross-reactions with various metabolites of WF were low (0.1-4%) except for 4''-hydroxy-WF, as were cross-reactions with the opposite enantiomer (0.3-3%). Assays were developed and used to determine enantiomer half-lives in rats dosed with racemic WF. Results were consistent with those found previously by administration of individual enantiomers, thus indicating the utility of the radioimmunoassay method.