Simultaneous quantification of α-/β-diastereomers of arteether, sulphadoxine and pyrimethamine: A promising anti-relapse antimalarial therapeutic combination, by liquid chromatography tandem mass spectrometry

A rapid, sensitive, selective and specific HPLC/ESI-MS/MS assay method was developed and validated for the simultaneous quantitation of α-/β-diastereomers of arteether (AE), sulphadoxine (SDX) and pyrimethamine (PYR) in rat blood plasma using propyl ether analogue of β-arteether as internal standard. The method involved a single-step, liquid–liquid extraction with ethyl acetate and the analytes were chromatographed on a C18 chromatographic column by isocratic elution with methanol:ammonium acetate buffer (10 mM, pH 4) (90:10%, v/v) and analyzed by tandem mass spectrometry. The run time was 4.5 min and the weighted (1/x2) calibration curves were linear over a range of 0.78–400 ng ml−1. The method was validated fully and the lower limit of quantification (LLOQ) in plasma was 0.78 ng ml−1 for all the analytes. The intra- and inter-day precision and accuracy were found to be well within the acceptable limits (<15%) and the analytes were stable after three freeze–thaw (f–t) cycles. The absolute recoveries were consistent and reproducible. The assay method was applied to pre-clinical pharmacokinetic interaction studies of α-/β-AE, SDX and PYR in rats.