Determination of S/R ratio of mephenytoin in human urine by chiral HPLC and ultraviolet detection and its comparison with gas chromatography.

AIM: To improve HPLC method for rapid determination of urinary S/R-ratio of mephenytoin, a widely used metabolic index for cytochrome P-450 2C19 (CYP2C19) activity.

METHODS

Aliquots of 0-8-h urine sample after dosing racemic mephenytoin 100 mg underwent one-step extraction with dichloromethane. Analysis was performed on a chiral column (250 mm x 4 mm, 5 microns) at lambda = 207 nm. The eluent was a mixture of acetronitrile and water containing both 0.1% glacial acetic acid and 0.2% triethylamine (14:86, vol/vol) at a flow-rate of 0.9 mL.min-1.

RESULTS

The enatiomers of mephenytoin in urine were well separated within 9 min. A linear correlation was observed between 50-5000 micrograms.L-1 with the detection limit of 12.5 micrograms.L-1 for both enantiomers of mephenytoin. This HPLC analysis was comparable to gas chromatography in accuracy and sensitivity, but with much shorter retention time and better resolution.

CONCLUSION

The present HPLC method is good for rapid determination of the ability of subjects to hydroxylate S-mephenytoin after oral administration of the racemic drug.