A liquid chromatography–mass spectrometry assay for simultaneous determination of two antimalarial thiazolium compounds in human and rat matrices

A new class of antimalarial drugs targeting phospholipid metabolism of the malarial parasite is now in development. In the strategy of this development, two mono-thiazolium salts, T1 and T2, need to be monitored. A liquid chromatography–mass spectrometry (LC–MS) method has been developed and validated according to FDA guidelines for simultaneous determination of T1 and T2 in plasma, whole blood and red blood cells (RBCs) from human and rat. The sample-pre-treatment procedure involved solid phase extraction after protein precipitation. Chromatography was carried out on a Zorbax eclipse XDB C8 column and mass spectrometric analysis was performed using an Agilent 1100 quadrupole mass spectrometer working with an electrospray ionization source. LC–MS data were acquired in single ion monitoring mode at m/z 312, 326 and 227 for T1, T2 and the internal standard (T3), respectively. The drug/internal standard peak area ratios were linked via a quadratic relationship to concentrations (human and rat plasma: 2.25–900 μg/l; human blood and rat RBCs: 4.5–900 μg/kg). Precision was below 14.5% for T1 and below 13% for T2. Accuracy was 92.6–111% for T1 and 95.6–108% for T2. Extraction recoveries were ≥85% in plasma and ≥53% in blood and RBCs. For T1 and T2, the lower limits of quantitation were 2.25 μg/l in plasma, and 4.5 μg/kg in whole blood and RBCs. Stability tests under various conditions were also investigated. This highly specific and sensitive method was useful to analyse samples from pharmacokinetic studies carried out in rat and would also be useful in clinical trials at a later stage.