Liquid chromatography–tandem mass spectrometry for the determination of paclitaxel in rat plasma after intravenous administration of poly(l-glutamic acid)-alanine-paclitaxel conjugate

A specific and sensitive liquid chromatography–tandem mass spectrometric method for quantitative determination of paclitaxel in rat plasma was developed and validated using docetaxel as an internal standard. Liquid-liquid extraction using tert-butyl methyl ether was used to extract the drug and the internal standard from plasma. The separation of paclitaxel was performed on a C18 column with a mobile phase of acetonitrile:water:formic acid (65:35:0.1, v/v/v) over 5 min. The assay was based on the selected reaction monitoring transitions at m/z of the precursor-product ion transitions m/z 854.2 → 286.1 for paclitaxel and 808.3 → 527.2 for internal standard. The lower limit of quantification was 0.5 ng/mL based on 100 μL of plasma. Intra- and inter-day assay variations were less than 15%, and the accuracy values were between 95.4 and 105.4%. The extraction recoveries ranged from 96.7 to 103.7% across the calibration curve range. The method was successfully applied to measurement of low concentrations of paclitaxel or regenerated paclitaxel in plasma after intravenous administration of a single dose (10 mg/kg) of a poly(l-glutamic acid)-alanine-paclitaxel conjugate to rats.