Determination of paclitaxel in mouse plasma and brain tissue by liquid chromatography–mass spectrometry

Paclitaxel is an anticancer agent extracted from the bark of the yew tree and is widely used in chemotherapy for solid tumors, including non-small cell lung cancer and ovarian carcinoma. Most assays to measure paclitaxel in plasma require a large amount of sample (0.4–1 ml) to achieve the necessary sensitivity, and are not suitable when only small sample sizes are available. To circumvent this latter limitation, we developed a sensitive liquid chromatography–mass spectrometry (LC–MS) method for the determination of paclitaxel in plasma based on the use of small sample volumes (50 μl plasma). A solid phase extraction procedure was employed that enabled the eluent to be directly injected onto a reversed phase chromatographic HPLC system using positive electrospray ionization followed by mass spectrometric detection. The extraction recoveries of paclitaxel were 98 and 83% from plasma and brain tissues, respectively. The mobile phase consisted of 50% acetonitrile in 0.1% formic acid that was pumped at 0.2 ml/min to yield a retention time for paclitaxel of 6.2 and 5.4 min for cephalomannine, the internal standard. The method has been validated at paclitaxel plasma concentrations from 0.036 to 9.9 μg/ml, and from 0.054 to 1.96 μg/ml in brain homogenates. A sensitive and specific assay for paclitaxel has been developed that has the advantages of using small sample sizes, and a single extraction step without solvent evaporation.