Simultaneous quantification of 22R and 22S epimers of budesonide in human plasma by ultra-high-performance liquid chromatography–tandem mass spectrometry: Application in a stereoselective pharmacokinetic study

Budesonide (BUD) is used as a mixture of 22R and 22S epimers for the topical treatment of asthma, rhinitis, and inflammatory bowel disease. To study stereoselectivity in the pharmacokinetics of each epimer, we developed a stereoselective and sensitive ultra-high-performance liquid chromatography–tandem mass spectrometry method for the quantitative determination of 22R and 22S epimers of BUD in human plasma. The epimers of BUD were extracted from plasma using n-hexane/dichloromethane/isopropanol (2:1:0.1, v/v/v) under alkaline conditions. Baseline separation was obtained within 7 min on an Acquity UPLC BEH C18 (50 mm × 2.1 mm, 1.7 μm) column using an isocratic mobile phase consisting of acetonitrile/5 mM ammonium acetate/acetic acid (29:71:0.142, v/v/v) at a flow rate of 0.7 mL/min. Mass spectrometric detection was performed in a multiple reaction monitoring mode using the m/z 489 → 357 transition for BUD epimers and the m/z 497 → 357 transition for the internal standard d8-BUD epimers. Calibration curves were linear over the concentration ranges of 5.0–500 and 5.0–3000 pg/mL for 22R-BUD and 22S-BUD, respectively. The lower limit of quantification was 5.0 pg/mL for both epimers. The method was successfully applied in a pharmacokinetic study of BUD controlled-release capsules in humans. Consistent differences in the pharmacokinetics of the 22R and 22S epimers were observed, the AUC(0–∞) of 22S-BUD was approximately six times higher than that of 22R-BUD, and the 22S-/22R-BUD ratio of total body clearance was 0.17.