Development and validation of a highly sensitive LC-MS/MS method for simultaneous quantitation of ethionamide and ethionamide sulfoxide in human plasma: Application to a human pharmacokinetic study

Abstract

A highly sensitive and specific LC-MS/MS method has been developed for simultaneous quantification of ethionamide and ethionamide sulfoxide in human plasma (300μL) using prothionamide as an internal standard (IS). Solid-phase extraction was used to extract ethionamide, ethionamide sulfoxide and IS from human plasma. The chromatographic separation of ethionamide, ethionamide sulfoxide and IS was achieved with a mobile phase consisting of 0.1% acetic acid:acetonitrile (20:80, v/v) at a flow rate of 0.50mL/min on a Peerless Basic C18 column. The total run time was 3.5min and the elution of ethionamide, ethionamide sulfoxide and IS occurred at 2.50, 2.18 and 2.68min, respectively. A linear response function was established for the range of concentrations 25.7-6120ng/mL (r > 0.998) for ethionamide and 50.5-3030ng/mL (r > 0.998) for ethionamide sulfoxide. The intra- and inter-day precision values for ethionamide and ethionamide sulfoxide met the acceptance as per FDA guidelines. Ethionamide and ethionamide sulfoxide were stable in battery of stability studies, viz. bench-top, autosampler and freeze-thaw cycles. The developed assay was applied to a pharmacokinetic study in humans. © 2011 John Wiley & Sons, Ltd.