A Novel Polarity Switching LC-MS/MS Method for Simultaneous Quantification of Drospirenone and Estetrol: Application to Pharmacokinetic Studies in Human Plasma.

A sensitive, selective, and rapid liquid chromatography-tandem mass spectrometry (LC-MS/MS) method using a polarity switch technique was developed and validated for the simultaneous determination of drospirenone (DSP) and estetrol (E4) in human plasma for the first time. Solid phase extraction (SPE) with Bond Elut PLEXA cartridges was performed. Chromatographic separation was obtained on Eclipse XDB-C8 (150 mm × 4.6 mm, 3.5 μm) column using 2-mM ammonium bicarbonate solution:methanol (30:70, v/v) as the mobile phase at a flow rate of 0.750 mL/min. A polarity switching method was performed in a triple quadrupole mass spectrometer using multiple reaction monitoring (MRM). MRM was performed in positive mode for DSP transitions m/z 367.2 → 171.1 and DSP-D4 transitions m/z 371.2 → 171.1, and in negative mode for E4 transitions m/z 303.1 → 241.2, 273.0 and E4-d3 transitions m/z 306.2 → 243.2, 275.0. Calibration curves were linear over the concentration ranges of 0.351-100.446 and 0.351-50.134 ng/mL for DSP and E4, respectively. The accuracy measured for both analytes ranged from -2.74% to 4.21%. Both the analytes showed consistent recoveries ranged from 77.25% to 81.34% with no significant matrix effect. The method was successfully applied in a pharmacokinetic study of DSP and E4 tablets (3 mg + 14.2 mg).