Validation and Application of an Online Extraction and Liquid Chromatography Tandem Mass Spectrometry Assay for the Analysis of Delamanid and Its DM-6705 Metabolite in Human Breast Milk

We developed and validated a bioanalytical assay to quantify delamanid and its key metabolite (DM-6705) in breast milk and aimed to quantify the secretion of these compounds in breast milk. Due to the hydrophobic nature of the analytes, special care was taken during sample preparation to prevent the formation of fatty deposits during protein precipitation. This was followed by online solid phase extraction and liquid chromatography with tandem mass spectrometry for detection. A Restek Viva BiPh C18 column (1.0mm×50mm, 5µm) was used for extraction while chromatographic separation was performed using a Waters Xterra MS C18 (2.1mm×100mm, 5 μm) analytical column with an isocratic mobile phase consisting of acetonitrile, methanol, and 5mM ammonium carbonate. The mass spectrometric detection of the analytes was performed using an AB Sciex 3200 mass spectrometer employing electrospray ionisation in the positive mode with multiple reaction motoring of the relevant precursor and product ions. Delamanid-d4 and OPC-14714 were used as internal standards. A quadratic (weighted 1/x concentration) regression was used to fit calibration curves for delamanid and DM-6705 over the concentration range of 10.0 – 1000ng/mL. The intra- and inter-day validation accuracies of the quality control samples were between 92.1% and 98.3% for delamanid, and 97.0% and 102.8% for DM-6705. The percentage coefficient of variation (precision) was less than 7.8%. To our knowledge, this is the first report describing the concentrations of delamanid and DM-6705 in the breast milk of patients treated for rifampicin-resistant tuberculosis.