High Performance Liquid Chromatographic Analysis of Cilostazol in Human Plasma with On‐Line Column Switching

An analytical method of cilostazol, antiplatelet agent, in human plasma was developed using a semi‐microbore HPLC equipped with an automated column switching system. After human plasma was diluted 1:2 with water and deproteinized, the fraction of analyte was injected onto a Capcell Pak MF Ph‐1 column (20 mm × 4 mm I.D.). The cilostazol fraction was transferred from the MF Ph‐1 column to an intermediate C18 column (35 mm × 2 mm I.D.) using 10% acetonitrile in water at a flow‐rate of 1 mL/min. The main separation was performed on a semi‐microbore C18 column (250 mm × 1.5 mm I.D.) using 40% acetonitrile in water at a flow‐rate of 150 µL/min. The retention time of cilostazol was about 19 min. The limit of quantitative analysis was 25 ng/mL. The accuracy of the assay was from 93.94% to 115.54%, while the intra‐ and inter‐day coefficient of variation (C.V.) of the same concentration range was less than 15%. The mean recovery was 98.9% and the responses were linear (r 2 > 0.999) over the concentration range of 25–2000 ng/mL. This analytical method showed excellent sensitivity, reproducibility, specificity, and speed using the plasma sample. This method could be suitable for the pharmacokinetic study of cilostazol in healthy volunteers, without time‐consuming sample preparation after oral administration.