Direct chiral LC-MS/MS analysis of fexofenadine enantiomers in plasma and urine with application in a maternal-fetal pharmacokinetic study.

This study shows the development and validation of two enantioselective LC-MS/MS methods for the determination of fexofenadine in biological matrices including the elution order determination. Plasma (200 µL) or urine (50 µL) aliquots were added to the internal standard solution [(S)-(-)-metoprolol] and extracted in the acid medium with chloroform. Resolution of the (R)-(+)- and (S)-(-)-fexofenadine enantiomers was performed in a Chirobiotic V column. The methods showed linearity at the range of 0.025-100 ng/mL plasma and 0.02-10 µg/mL urine for each fexofenadine enantiomer. These methods were applied to the maternal-fetal pharmacokinetics of fexofenadine enantiomers in plasma and urine of parturient women (n = 8) treated with a single oral 60 mg dose of racemic fexofenadine. Enantiomeric ratio in plasma (AUC0-∞(R)-(+)/(S)-(-)) was close to 1.5, nevertheless in urine was closed to unity. The transplacental transfer was approximately 18% for both fexofenadine enantiomers. The enantioselective methods can also be useful in future clinical studies of chiral discrimination of drug transporters.