Liquid chromatographic assay of nifedipine in human plasma and its application to pharmacokinetic studies

A highly sensitive, selective and reproducible reversed-phase high-performa nce liquid chromatographic method has been developed for the determination of nifedipine iii human plasma with minimum sample preparation. The method is sensitive to 3 ng/ml in plasma, with acceptable within- and between-day reproducibilities and linearity (r(2) > 0.99) over a concentration range fr om 10-200 ng/ml. Acidified plasma samples were extracted using diethyether containing diazepam as internal standard and chromatographic separation was accomplished on C-18 column using a mobile phase consisting of acetonitril e, methanol and water (35:17:48, v/v). The within-day precision ranged from 2.22 to 4.64% and accuracy ranged from 102.4-106.4%. The day-to-day precis ion ranged from 2.34-7.07% and accuracy from 95.1-100.1%. The relative reco veries of nifedipine from plasma ranged from 91.0-107.3% whereas extraction recoveries were 88.6-93.3%. Following eight 6-week freeze-thaw cycles, nif edipine in plasma samples proved to be stable with accuracy ranging from 0. 64 to 3.0% and precision ranging from 3.6 to 4.15%. Nifedipine was also fou nd to be photostable for at least 120 min in plasma, 30 min in blood and fo r 60 min in aqueous solutions after exposure to light. The method is sensit ive and reliable for pharmacokinetic studies and therapeutic drug monitorin g of nifedipine in humans after the oral administration of immediate-releas e capsules and sustained-release tablets to five healthy subjects. (C) 2000 Elsevier Science B.V. All rights reserved.