Liquid chromatographic determination of nifedipine in plasma and of its main metabolite in urine.

A high-performance liquid chromatographic method was developed for the assay of nifedipine in plasma and its main metabolite (M-I) in urine. After liquid-liquid extraction nifedipine was chromatographed in a reversed-phase system with ultraviolet detection at 238 nm. The method was sensitive to 2 ng nifedipine per ml plasma and the standard curve was linear to at least 400 ng/ml. Standard deviations did not exceed 8.5%. There was no interference with photodecomposition products or metabolites. M-I was determined in urine after liquid-liquid extraction by ion-pair chromatography with ultraviolet detection at 290 nm. The method was sensitive to 0.02 micrograms M-I per ml urine and the standard curve was linear to at least 5 micrograms/ml. Standard deviations did not exceed 5.0%. The methods were used to study nifedipine disposition in healthy volunteers.