Simultaneous quantification of fexofenadine and pseudoephedrine in human plasma by liquid chromatography/tandem mass spectrometry with electrospray ionization: method development, validation and application to a clinical study

To support the pharmacokinetic and bioavailability study of a once‐daily fexofenadine/pseudoephedrine combination, a high‐performance liquid chromatography/positive ion electrospray tandem mass spectrometry (HPLC/ESI‐MS/MS) method for the simultaneous quantification of fexofenadine and pseudoephedrine was developed and validated with 500 µL human plasma using mosapride as an internal standard (IS). Following solid‐phase extraction, the analytes were separated using an isocratic mobile phase on a reversed‐phase column and analyzed by MS/MS in the multiple reaction monitoring mode using the respective [M+H]+ ions, m/z 502/466 for fexofenadine, m/z 166/148 for pseuoephedrine and m/z 422/198 for the IS. The method exhibited linear dynamic ranges of 1–500 ng/mL and 2–1000 ng/mL for fexofenadine and pseudoephedrine, respectively, in human plasma. The lower limits of quantification were 1 and 2 ng/mL with a relative standard deviation of less than 10% for fexofenadine and pseudoephedrine, respectively. Acceptable precision and accuracy were obtained for concentrations over the standard curve range. The total chromatographic run time was 2 min and more than 400 human plasma samples could be analyzed in one day by running the system overnight. The method is precise and sensitive enough for its intended purpose. Copyright © 2006 John Wiley & Sons, Ltd.