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Pivmecillinam, the ester of biologically active antibiotic mecillinam, is an effective oral preparation to treat urinary tract infections. To study pharmacokinetics in humans, LC‐MS/MS methods were developed to quantify pivmecillinam and mecillinam in human plasma, respectively. Considering cephalexin as internal standard, analytes were separated on UltimateXB‐C18 columns after protein precipitation by acetonitrile. The mobile phase was composed of water containing 0.1% formic acid and methanol. The multiple reactions monitoring transitions of m/z 440.2→167.1, 326.1→167.1, and 348.1→158.1 were selected to inspect pivmecillinam, mecillinam, and the internal standard in positive ion mode. No apparent matrix effect was perceived. Linearities were obtained over calibration ranges of 0.0500–12.0 and 10.0–15,000 ng/mL, respectively. The intraday precisions were below 5.5%, the interday precisions were below 6.1%, and accuracies were within –8.1 to 13.0%. Stability tests were conducted and an acidification step was explored to enhance the stability of pivmecillinam and mecillinam. Further stability was validated under various storage and processing conditions. Both methods were applied to a pharmacokinetic study of pivmecillinam and mecillinam after oral administration of 400 mg pivmecillinam hydrochloride tablets in healthy Chinese subjects. [ABSTRACT FROM AUTHOR]

Regadenoson, the first selective adenosine A2A receptor agonist, is used to perform exercise stress test during radionuclide myocardial perfusion imaging. To detect the concentration of regadenoson in human plasma, a simple, fast, and sensitive tandem mass spectrometry method was established herein. Acetonitrile was used as a protein precipitation agent. Chromatographic separation was completed in 6.5 min using a BEH HILIC column (50 × 2.1 mm, 1.7 μm). The mobile phase consisted of 10 mmol/L ammonium acetate/acetonitrile (gradient elution). To quantify regadenoson and regadenoson‐d3, an API 4000 mass spectrometry in multiple reaction monitoring mode with transitions of 391.3→259.2 and 394.3→262.2, respectively, was utilized. The calibration curve was linear in the range of 0.100–50.0 μg/L, and the intrabatch and interbatch precisions were <9.7% and <13.0%, respectively, and the accuracy was 2.0–6.9%. There was no apparent matrix effect for regadenoson or regadenoson‐d3. The developed method was used to study the pharmacokinetic characteristics of regadenoson in healthy Chinese subjects. [ABSTRACT FROM AUTHOR]

Proton pump inhibitors, including omeprazole, rabeprazole, lansoprazole, and pantoprazole, achieved simultaneous enantioselective determination in the human plasma by chiral liquid chromatography–tandem mass spectrometry. The four corresponding stable isotope‐labeled proton pump inhibitors were adopted as the internal standards. Each enantiomer and the internal standards were extracted with acetonitrile containing 0.1% ammonia, then separated with a Chiralpak IC column (5 µm, 4.6 mm × 150 mm) within 10 min. The mobile phase was composed of acetonitrile–ammonium acetate (10 mM) containing 0.2% acetic acid (50:50, v/v). To quantify all enantiomers, an API 4000 tandem mass spectrometer was used, and multiple reaction monitoring transitions were performed on m/z 360.1→242.1, 384.1→200.1, 370.1→252.1, and 346.1→198.1, respectively. No significant matrix effect was observed for all analytes. The calibration curve for all enantiomers were linear from 1.25 to 2500 ng/mL. The precisions for intra‐ and inter‐run were < 14.2%, and the accuracy fell in the interval of –5.3 to 8.1%. Stability of samples was confirmed under the storage and processing conditions. The developed method was also suitable for separation and determination of ilaprazole enantiomers. The validated method combining the equilibrium dialysis method was applied to the protein binding ratio studies of four pairs proton pump inhibitor enantiomers in human plasma. [ABSTRACT FROM AUTHOR]