Application of a rapid and selective method for the simultaneous determination of carebastine and pseudoephedrine in human plasma by liquid chromatography-electrospray mass spectrometry for bioequivalence study in Korean subjects

We describe a simple, rapid and sensitive high-performance liquid chromatography - electrospray ionization tandem mass spectrometric method that was developed for the simultaneous determination of carebastine and pseudoephedrine in human plasma using cisapride as an internal standard. Acquisition was performed in multiple-reaction monitoring mode by monitoring the transitions: m/z 500.43 > 167.09 for carebastine and m/z 166.04 > 147.88 for pseudoephedrine. The devised method involves a simple single-step liquid - liquid extraction with ethyl acetate. Chromatographic separation was performed on a C₁₈ reversed-phase chromatographic column at 0.2 mL/min by isocratic elution with 10 mM ammonium formate buffer - acetonitrile (30:70, v/v; adjusted to pH 3.3 with formic acid). The devised method was validated over 0.5 - 100 ng/ mL of carebastine and 5 - 1000 ng/mL of pseudoephedrine with acceptable accuracy and precision, and was successfully applied to a bioequivalence study involving a single oral dose (10 mg of ebastine plus 120 mg of pseudoephedrine complex) to healthy Korean volunteers.