Simultaneous determination of ebastine and its three metabolites in plasma using liquid chromatography-tandem mass spectrometry

We developed a method for determining ebastine, a new generation of antihistamines, and its three metabolites (hydroxyebastine, carebastine and desalkylebastine) in plasma simultaneously using LC/MS/MS. Four compounds and terfenadine. an internal standard, were extracted from plasma using a mixture of diethylether and dichloromethane in the presence of I M HCl After drying the organic layer, the residue was reconstituted in mobile phase (acetonitrile:5 mM ammonium acetate, 50:50, v/v) and injected onto a reversed-phase C-18 column. The isocratic mobile phase was eluted at 0.2 ml/min. The ion transitions monitored in multiple reaction-monitoring mode were InIz. 470.7 --> 167.1, 486.7 --> 167.1, 500.6 --> 167.1, 268.4 --> 167.1 and 472.7 --> 436.0 for ebastine, hydroxyebastine, carebastine, desalkylebastine and terfenadine, respectively. The coefficient of variation of the assay precision was less than 12.5%, and the accuracy exceeded 88%. The limit of detection was 0.5 ng/ml for desalkylebastine; 0.2 ng/ml for ebastine, hydroxyebastine and carebastine, respectively. This method was used to measure the plasma concentration of ebastine and its three metabolites from healthy subjects after a single 20 mg oral dose of ebastine. This analytic method is a very simple, sensitive, and accurate to determine the pharmacokinetic profiles of ebastine including its metabolites. (C) 2004 Elsevier B.V. All rights reserved.