Trace-level quantitation of iralukast in human plasma by microbore liquid chromatography/tandem mass spectrometry

Iralukast (CGP 45715A) is a potent peptido-leukotriene antagonist that is a ctive in various in vitro and animal models for the treatment of asthma. An analytical challenge was to develop a sensitive liquid chromatography/tand em mass spectrometry (LC/MS/MS) method with a lower limit of quantitation ( LLOQ) of 10 pg/mL for the analysis of iralukast when administered at low do ses during clinical trials. Several issues had to be addressed in order to devise a LC/MS/MS assay for the above compound. First, iralukast appeared t o be light sensitive and unstable at room temperature under acidic conditio ns. Second, a LLOQ of 10 pg/mL was needed to support several clinical trial s. Third, positive electrospray ionization of iralukast did not yield the n ecessary sensitivity required for studies in humans. Consequently, LC/MS/MS conditions were optimized for the negative ion mode of detection. Fourth, sample preparation steps proved to be critical to reduce the possibility of microbore HPLC column (50 mm x 1.0 mm i.d,) obstruction, chromatographic d eterioration, and matrix-mediated electrospray ion suppression. While our v alidated method addressed the above challenges, its major drawback was limi ted sample throughput capability, Nonetheless, plasma concentration-time pr ofiles for patients with moderate asthma after oral administration of 200, 500, 1000, and 5000 mu g/kg/day of iralukast were successfully obtained. Co pyright (C) 2000 John Wiley & Sons, Ltd.