Lori D. Payne, Katie J. Amrhein, and Melissa M. Kiser*
Bioanalytical Systems, Inc. McMinnville, OR
BASi® has analyzed thousands of samples for paclitaxel with a limit of quantification of 0.1 ng/mL and lower. This assay is performed using LCMS/MS to detect paclitaxel and a high-purity isotopically-substituted 13C6-paclitaxel as the internal standard.
This study was conducted to verify non-interference of common HIV and over-the-counter drugs in the sensitive LC-MS/MS method for paclitaxel in human plasma. Also, the study investigated the stability of paclitaxel to heat treatment to deactivate the HIV virus.
The method of analysis used for these tests was previously reported1. In short, a 0.400 mL plasma sample is fortified with a stable-label internal standard, extracted into MTBE, evaporated and reconstituted. The HPLC conditions consist of a 2.1 x 50 mm SB-C18 column maintained at 50C with a flow rate of 0.2 mL/min. The pseudo-molecular ions of thirteen HIV drugs (amprenavir, delavirdine, efavirene, indinavir, lopiravir, naltiravir, nevirapine, saquinavir, D4T, 3TC, abacavir, zidovudine, and tipranavir) and a panel of OTC drugs or their major metabolites (acetaminophen, caffeine, cotinine, nicotine, salicylic acid, ibuprofen, ketoprofen and naproxen) were monitored under the conditions of the assay. Additionally, plasma samples containing 0, 0.3 or 100 ng/mL paclitaxel were heat-treated at 56ÂºC for 30 min prior to being extracted. This procedure has been reported to inactivate the HIV virus.
1 Alexander, M.S., Kiser M.M., Culley T., Kern J.R., Dolan J.W., McChesney J.D, Zygmunt J., Bannister S.J. (2002). Measurement of paclitaxel in biological matricies: high-throughput liquid chromatographic-tandem mass spectrometric quantification of paclitaxel and metabolites in human and dog plasma. Journal of Chromatography B (785, 253-261).
Mass spectrometric analysis was performed on a MicroMass Quattro Ultima triple quadrupole mass spectrometer using an electrospray interface. The MS was operated in positive ion mode. Detection was by multiple reaction monitoring observing the following transitions:
Paclitaxel 854 > 286 amu
13C6Paclitaxel 860 > 292 amu
None of the HIV or OTC drugs tested eluted at the retention time of interest. No interferences were seen in the analyte or internal standard mass spectral channels. Heat treatment of the plasma resulted in no interferences in the blanks and acceptable accuracy (deviation from nominal <6%) and precision (CV<10%).
The presence of physiologically relevant concentrations of HIV or OTC drugs did not interfere with a sensitive LC-MS/MS assay for paclitaxel in human plasma. The assay has a validated LLOQ of 0.1 ng/mL. Treatment of samples with heat to inactivate the HIV virus prior to sample analysis also did not interfere with the quantification of paclitaxel in these samples. This method has been used to analyze samples from clinical studies.