A high-performance liquid chromatographic method for determination of mitragynine in serum and its application to a pharmacokinetic study in rats

A simple HPLC technique for determining mitragynine levels in serum was developed. The separation system consisted of a C18 column heated to 35°C, a methanol–water (80:20, v/v) mobile phase, a flow rate of 0.8 mL/min and detection in the ultraviolet at 225 nm. Mitragynine, with a retention time of 10.09 min, was well resolved from any interferences in human serum and the internal standard peak. The calibration curve was linear from 0.1 to 10 µg/mL (r = 0.9995). Extraction of mitragy‐nine from alkalinized serum using diethyl ether gave a high recovery (≥85%). The intra‐ and inter‐day precisions of the method were 4.29–5.88%RSD and 7.06–8.45%RSD, respectively. The accuracy ranged from −9.54 to +0.67%DEV. The limit of detection was 0.03 µg/mL and the lower limit of quantification was 0.1 µg/mL. Mitragynine in the stock solution was stable during 30 days of storage at 4°C. This method was successfully applied to determine the pharmacokinetic characteristics of mitragynine levels in the serum of rats after it was administered orally. Copyright © 2007 John Wiley & Sons, Ltd.