A single LC–tandem mass spectrometry method for the simultaneous determination of four H2 antagonists in human plasma

A sensitive and universal LC–MS/MS method for the simultaneous determination of famotidine, cimetidine, ranitidine and lafutidine in human plasma was presented. This is the first single LC–MS/MS method reported for the simultaneous analysis of these four H2 antagonists in human plasma. Following liquid–liquid extraction with ethyl acetate, the separation was performed on an Agilent Zorbax SB-CN (150 mm × 2.1 mm I.D., 5 μm) column using a mobile phase consisted of methanol:20 mM ammonium acetate (55:45, v/v). The total run time was 7 min per sample. Quantification was performed by electrospray ionization–triple quadrupole mass spectrometry by selected reaction monitoring (SRM) detection in the positive mode. All calibration curves showed good linear regression (r2 > 0.99) from 0.5 to 1000 ng/mL for famotidine and lafutidine, and 5–20,000 ng/mL for cimetidine and ranitidine. The method showed good precision and accuracy with overall intra- and inter-day variations of 1.37–9.29% and 3.51–9.40%, respectively. The assay was successfully applied to a bioequivalence study using ranitidine as the model compound.