Preparation of standard and quality control (QC) samples
Stock standard solutions of Favipiravir were prepared in methanol at a concentration of 5 mg/mL. Working solutions in the concentration range of 1.6-600 µg/mL were prepared by diluting with methanol. The working IS was prepared in methanol at a concentration of 10 µg/mL. Stock solutions of Favipiravir and IS were stored at -20 °C.
Calibration standards were prepared by spiking the appropriate amounts of standard solutions into blank plasma to obtain final concentration levels of 80, 160, 1000, 5000, 10000, 20000, 27000, 30000 ng/mL. The quality control samples were prepared similarly, at concentrations of 80, 240, 1500, 12000 and 24000 ng/mL. The lower limit of quantification (LLOQ), using 100 μL human plasma, was 80 ng/mL. Calibration standards and QC samples were stored at -70◦C freezer until analysis.