First detection/quantification of roxadustat in hair with a new liquid chromatography with tandem mass spectrometry method: Application to a treated patient.

Roxadustat is an oral inhibitor of hypoxia-inducible factor prolyl hydroxylase which increases erythropoiesis. It can therefore be used as a doping agent. No data are available on how to measure roxadustat in hair and on the concentration found in treated patients. The aim of this study was to develop a liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for the quantification of roxadustat in hair and to apply it to a chronically treated patient. After decontamination with dichloromethane, testosterone-D3 used as an internal standard and phosphate buffer pH 5.0 were added to 20 mg of hair and incubated for 10 min at 95 °C. Four ml of dichloromethane were used for extraction and reconstituted into the mobile phase, 10 µL were injected into the chromatographic system. The method was linear in the range 0.5-200 pg/mg, accurate and precise (evaluated at 3 levels) and was successfully applied to measure roxadustat in a brown-haired patient treated pharmacologically with 100-120 mg 3 days a week. Results were stable between 41 and 57 pg/mg in the 6 proximal 1 cm segments. This first method describing the measurement of roxadustat in hair appears to be suitable for the quantification of this compound in clinical or doping control cases.