Liquid chromatography and tandem mass spectrometry for the quantitative determination of ixabepilone (BMS-247550, Ixempra) in human plasma: method validation, overcoming curve splitting issues and eliminating chromatographic interferences from degradants.

A sensitive method was developed and validated for the measurement of ixabepilone (BMS-247550, Ixempra) using a demethylated analogue of ixabepilone (BMS-212188) as an internal standard. A 0.050 mL portion of each plasma sample was extracted with 0.450 mL of acetonitrile containing the internal standard via protein precipitation. The supernatant was analyzed on a LC-MS/MS system. Chromatography was carried out on a 2.0 mm x 100 mm YMC ODS-AQ 3 microm column using an isocractic mobile phase consisting of acetonitrile:10 mM ammonium acetate, pH 5.0 (70:30, v/v) at a flow rate of 0.30 mL/min. The mass spectrometer was fitted with a TurboIonSpray source and operated in negative ionization mode. Detection of ixabepilone and BMS-212188 were accomplished using multiple reaction monitoring (MRM) of precursor>product ion pairs of m/z 505.2>405.2, and 492.1>392.1, respectively. The assay range was 2.00-500 ng/mL and was fitted to a 1/x(2) weighted quadratic regression model. Replicate sample analysis indicated that intra- and inter-day accuracy and precision are within +/-15.0%. The recovery of ixabepilone from 0.050 mL of plasma containing 5.00 and 400 ng/mL was greater than 94%. The method was demonstrated to be sensitive, selective and robust, and was successfully used to support clinical studies. This paper also discussed approaches used for resolving a curve splitting issue observed during quantitative analysis of ixabepilone in biological matrices. Finally, to adapt the methodology to pharmacokinetics of ixabepilone after oral administration, the potential interference of chemical degradants on the determination of ixabepilone was evaluated.