Simultaneous quantification of 19 analytes in breast milk by liquid chromatography-tandem mass spectrometry (LC-MS/MS)

A bioanalytical method by high performance liquid chromatography coupled to mass spectrometry (HPLC-MS/MS) for the simultaneous quantification of 17 drugs and 2 major active metabolites in breast milk was developed and validated. Breast milk samples (100 μL) were submitted to a simple protein precipitation for the extraction of the analytes after the addition of deuterated internal standards (10 μL). A Kinetex C8 column was used for the separation of analytes with mobile phases composed of acetonitrile with 0.1 % formic acid and water with 0.1 % formic acid in gradient elution mode. Analytes were detected using an AB/SCIEX 4000 QTRAP instrument with positive electrospray ionization and operating in scheduled multiple reaction monitoring mode. Validation covered a large range of concentrations (0.5-500 ng/mL) for most of the analytes except bisoprolol, lacosamide, vilazodone (1-500 ng/mL), acid mycophenolic, letrozole, clomiphene (2-500 ng/mL) and hydroxy-melatonin (10-500 ng/mL). Within-run and between-run accuracy and precision for 4 levels of quality controls (QC) spiked at the lower limit of quantification (LLOQ), at 3 times the LLOQ, 50 % of the upper limit of quantification (ULOQ) and 80 % of the ULOQ were in agreement with the criteria from international guidelines. Matrix effect and extraction recovery ranged from 40.7 to 106.5 % and 87.3 to 110.8 %, respectively with relative standard deviations less than 15 %. Furthermore, all analytes were stable in breast milk at room temperature for 24 h, at -20 °C for two weeks, at -80 °C for 1 month, and after 3 freeze-thaw cycles. Finally, the method was successfully applied to nursing women samples collected from an ongoing feasibility study on drug quantification in breast milk.