Quantification of plasma remdesivir and its metabolite GS-441524 using liquid chromatography coupled to tandem mass spectrometry. Application to a Covid-19 treated patient

Objectives: A method based on liquid chromatography coupled to triple quadrupole mass spectrometry detection using 50 mu L of plasma was developed and fully validated for quantification of remdesivir and its active metabolites GS-441524. Methods: A simple protein precipitation was carried out using 75 mu L of methanol containing the internal standard (IS) remdesivir-C-13(6) and 5 mu L ZnSO4 1 M. After separation on Kinetex (R) 2.6 mu m Polar C18 100A LC column (100 x 2.1 mm i.d.), both compounds were detected by a mass spectrometer with electrospray ionization in positive mode. The ion transitions used were m/z 603.3 -> m/z 200.0 and m/z 229.0 for remdesivir, m/z 292.2 -> m/z 173.1 and m/z 147.1 for GS-441524 and m/z 609.3 -> m/z 206.0 for remdesivir-C-13(6). Results: Calibration curves were linear in the 1-5000 mu g/L range for remdesivir and 5-2500 for GS-441524, with limit of detection set at 0.5 and 2 mu g/L and limit of quantification at 1 and 5 mu g/L, respectively. Precisions evaluated at 2.5, 400 and 4000 mu g/L for remdesivir and 12.5, 125, 2000 mu g/L for GS441524 were lower than 14.7% and accuracy was in the [89.6-110.2%] range. A slight matrix effect was observed, compensated by IS. Higher stability of remdesivir and metabolite was observed on NaF-plasma. After 200 mg IV single administration, remdesivir concentration decrease rapidly with a half-life less than 1 h while GS-441524 appeared rapidly and decreased slowly until H-24 with a half-life around 12 h. Conclusions: This method would be useful for therapeutic drug monitoring of these compounds in Covid-19 pandemic.