SIMPLE AND EFFICIENT HPLC-UV QUANTITATION OF ETOPOSIDE AND ITS CIS-ISOMER IN RAT MICRO-VOLUME PLASMA AND TISSUE SAMPLES: APPLICATION TO PHARMACOKINETIC AND BIODISTRIBUTION STUDIES

Abstract

The present study was aimed at developing a validated HPLC method to quantify the sufficiently low concentrations of etoposide and its cis-isomer in plasma and tissue samples with emphasize on (1) employing a conventional UV detector, (2) using a low biological sample size and a minimized organic solvent volume, and (3) providing precise information about the conversion of etoposide to its cis-isomer in biological samples. The analysis was carried out on a monolithic C₁₈ column using a mixture of methanol, acetonitrile, and phosphate buffer (18:19:63, v/v/v) containing 0.007% triethylamine as the mobile phase. The analytes were detected using UV absorption at 285 nm. The sample preparation procedure involved the liquid-liquid extraction of analytes and IS from 100 µL plasma or 200 µL of tissue homogenates in 0.5–1 mL mixture of chloroform and n-hexane (80:20, v/v). The limit of detection of etoposide and its cis-isomer in plasma and tissue samples, with considering a signal-to-noise ratio of 3:1, was 20 ng/mL. Stability studies at room temperature indicated that etoposide in plasma samples was stable for only two hr, after which the trans-isomer was converted to the cis-isomer. The described method was successfully applied toward etoposide pharmacokinetic and tissue distribution studies in rats.

Keywords:

• etoposide
• HPLC-UV
• monolithic column
• pharmacokinetics
• rat plasma
• tissue distribution

ACKNOWLEDGMENTS

This research was supported by a grant from Shaheed Beheshti University of Medical Sciences, Tehran, Iran. The authors wish to thank Mrs. Zahra Abbasian for her technical help.

Notes

^a Percent of initial concentration (at zero time).

^a Percent of initial concentration (at zero time).

Data presented as mean ± SD.