Determination of mephenytoin stereoselective oxidative metabolism in urine by chiral liquid chromatography employing beta-cyclodextrin as a mobile phase additive.

A direct high-performance liquid chromatographic assay was developed for the separation and determination of S- and R-mephenytion enantiomers in human urine. Separation was achieved on a Supelcosil LC-8 column with methanol-0.1 M acetate buffer as the mobile phase and beta-cyclodextrin as a mobile phase additive. The urinary S/R enantiomeric ratio of mephenytoin was measured in a 32-h urine sample (as phenotypic traits) for determination of the ability of normal subjects to hydroxylate racemice mephenytoin after oral administration of the drug.