A new high-performance liquid chromatography-tandem mass spectrometry method for the determination of paclitaxel and 6[alpha]-hydroxy-paclitaxel in human plasma: Development, validation and application in a clinical pharmacokinetic study

Paclitaxel belongs to the taxanes family and it is used, alone or in multidrug regimens, for the therapy of several solid tumours, such as breast-, lung-, head and neck-, and ovarian cancer. Standard dosing of chemotherapy does not take into account the many inter-patient differences that make drug exposure highly variable, thus leading to the insurgence of severe toxicity. This is particularly true for paclitaxel considering that a relationship between haematological toxicity and plasma exposure was found. Therefore, in order to treat patients with the correct dose of paclitaxel, improving the overall benefit-risk ratio, Therapeutic Drug Monitoring is necessary. In order to quantify paclitaxel and its main metabolite, 6[alpha]-hydroxy-paclitaxel, in patients' plasma, we developed a new, sensitive and specific HPLC-MS/MS method applicable to all paclitaxel dosages used in clinical routine. The developed method used a small volume of plasma sample and is based on quick protein precipitation. The chromatographic separation of the analytes was achieved with a SunFire.sup.[TM] C18 column (3.5 [mu]M, 92 Å, 2,1 x 150 mm); the mobile phases were 0.1% formic acid/bidistilled water and 0.1% formic acid/acetonitrile. The electrospray ionization source worked in positive ion mode and the mass spectrometer operated in selected reaction monitoring mode. Our bioanalytical method was successfully validated according to the FDA-EMA guidelines on bioanalytical method validation. The calibration curves resulted linear (R.sup.2 [greater than or equal to]0.9948) over the concentration ranges (1-10000 ng/mL for paclitaxel and 1-1000 ng/mL for 6[alpha]-hydroxy-paclitaxel) and were characterized by a good accuracy and precision. The intra- and inter-day precision and accuracy were determined on three quality control concentrations for paclitaxel and 6[alpha]-hydroxy-paclitaxel and resulted respectively