Determination of betamethasone and betamethasone 17-monopropionate in human plasma by liquid chromatography–positive/negative electrospray ionization tandem mass spectrometry

This study presents a high-performance liquid chromatography–positive/negative electrospray ionization tandem mass spectrometric (LC–ESI(+/−)–MS–MS) method for the determination of betamethasone (BOH) and betamethasone 17-monopropionate (B17P) in human plasma using beclomethasone dipropionate as the internal standard (I.S.). Both compounds were extracted from human plasma with ether–cyclohexane (4:1, v/v) and were separated by HPLC on a Hanbon Lichrospher C18 column with a mobile phase of methanol–water (85:15, v/v) at a flow rate of 0.7 ml/min. Calibration curves were linear over the range of 0.10–50 ng/ml for BOH and 0.050–50 ng/ml for B17P. The inter-run relative standard deviations were less than 14.4% for BOH and 12.3% for B17P. The intra-run relative standard deviations were less than 9.3% for BOH and 7.9% for B17P. The mean plasma extraction recovery for BOH and B17P were in the ranges of 82.7–85.9% and 83.6–85.3%, respectively. The method was successfully applied to study the pharmacokinetics of a new formulation of betamethasone phosphate/betamethasone dipropionate injection in healthy Chinese volunteers.