Determination of unbound warfarin enantiomers in human plasma and 7-hydroxywarfarin in human urine by chiral stationary-phase liquid chromatography with ultraviolet or fluorescence and on-line circular dichroism detection.
Enantiomers of warfarin and 7-hydroxywarfarin in human plasma and urine, respectively, were determined by high-performance liquid chromatography using a cellulose-derivative column with UV or fluorescent detection, and their absolute configuration was determined simultaneously by a circular dichroism spectropolarimeter connected in series. Enantiomers of warfarin and its major metabolites [i.e., (R)-6-hydroxywarfarin, (S)-7-hydroxywarfarin and (RS)-warfarin alcohol] were well resolved. The method was precise and sensitive: within- and between-day coefficients of variation were <9.6% for warfarin enantiomers in plasma and <7.1% for 7-hydroxywarfarin enantiomers in urine, respectively, and the lower detection limits were 20 ng/ml for (R)-warfarin, 40 ng/ml for (S)-warfarin, 2.5 ng/ml for (R)-7-hydroxywarfarin and 4.5 ng/ml for (S)-7-hydroxywarfarin in 0.5 ml of both plasma and urine. The ultrafiltration technique was used for determining unbound concentrations of warfarin enantiomers in plasma using [14C]warfarin enantiomers resolved by the present HPLC system. Clinical applicability of the method was evaluated by determining unbound concentrations of warfarin enantiomers in five consecutive plasma samples obtained from a patient exhibiting an unstable anticoagulant response to warfarin (4 mg/day, p.o.). Results indicated that the present method would be useful in clarifying factors responsible for a large intra- and inter-patient variability in warfarin effects with regard to unbound plasma enantiomer pharmacokinetics.
Takahashi
H
H
Department of Pharmacotherapy, Meiji College of Pharmacy, Tanashi, Tokyo, Japan.
Kashima
T
T
Kimura
S
S
Muramoto
N
N
Nakahata
H
H
Kubo
S
S
Shimoyama
Y
Y
Kajiwara
M
M
Echizen
H
H
D000925:Anticoagulants / Q000097:blood* / Q000378:metabolism / Q000493:pharmacokinetics; D001798:Blood Proteins / Q000378:metabolism; D002853:Chromatography, Liquid; D002942:Circular Dichroism; D006801:Humans; D011485:Protein Binding; D012680:Sensitivity and Specificity; D013050:Spectrometry, Fluorescence; D013056:Spectrophotometry, Ultraviolet; D013237:Stereoisomerism; D014859:Warfarin / Q000031:analogs & derivatives* / Q000097:blood* / Q000378:metabolism / Q000493:pharmacokinetics / Q000652:urine
D000925:Anticoagulants; D001798:Blood Proteins; D014859:Warfarin; C087837:7-hydroxywarfarin