Highly sensitive liquid chromatography-electrospray mass spectrometry (LC-MS) method for the determination of etoposide levels in human serum and plasma.

Etoposide is one of the most commonly used antineoplastic agents. A highly sensitive liquid chromatography-electrospray mass spectrometry (LC-MS) method was developed for the determination of etoposide in human serum and plasma. Etoposide was extracted with chloroform and extracts were reconstituted in acetonitrile followed by the evaporation of chloroform with nitrogen gas. Etoposide was separated using Lichospher 100 RP-18 (5 microm) column (250 mmx4 mm) with the mobile phase of acetonitrile-water containing 0.1% acetic acid (45/55, v/v) at flow-rate of 0.5 ml/min. Selected-ion monitoring (SIM) mode was performed on m/z 589 (positive ion mode) using a fragmentor of 75 V. Good linearity (r>0.9965) was observed between concentrations of 0.0125-5 microM in 200 microl serum and 0.01-10 microM in 100 microl plasma. Intra- and inter-assay variabilities were less than 7% and the lowest detection limit of etoposide was 0.005 microM in both serum and plasma at a signal-to-noise ratio of approximately 4. The etoposide concentrations in four cancer patients treated with etoposide are also presented to demonstrate the clinical utility of this new method, which should aid the pharmacokinetically guided use of etoposide in clinical settings.