HPLC-DAD quantification of favipiravir in whole blood after extraction from volumetric absorptive microsampling devices

Favipiravir is a prodrug of T-1105 made by modifying the pyrazine group as a COVID-19 therapy. During the pandemic, a safe and comfortable biosampling technique is needed for the subject or patient. Volumetric Absorptive Microsampling (VAMS) is a biosampling technique with a small blood volume and minimum hematocrit effect. The aims of this study were to develop and validate an analytical method for quantifying favipiravir extracted from VAMS using High Performance Liquid Chromatography – Photodiode Array with remdesivir as an internal standard. Analysis of favipiravir was performed using a C(18) column (Waters, Sunfire™ 5 µm; 250 × 4.6 mm), with injection volume of 50 µL, flow rate of 0.8 mL/min, column temperature 30 ℃, and wavelength 300 nm. The separation was conducted under gradient elution with mobile phase consists of acetonitrile-0.2 % formic acid-20 mM sodium dihydrogen phosphate pH 3.5 and run time 12 min. Sample preparation was carried out using a protein precipitation method with 500 µL of methanol as precipitating agent. Samples were mixed on vortex for 30 s, sonicated for 15 min, and centrifuged at 10,000 rpm for 10 min. Lower Limit of Quantification (LLOQ) obtained was 0.5 µg/mL and the calibration curve ranged from 0.5 to 160 µg/mL. Sensitivity, linearity, selectivity, carry-over, accuracy, precision, recovery, and stability were validated by the guideline from Food and Drug Administration 2018. The method developed has successfully met the full validation requirements by FDA 2018 with the LLOQ obtained was 0.5 µg /mL.