A quality-by-design optimized LC method for navigating degradation kinetics and quantification of favipiravir in the presence of degradation products and manufacturing impurities

Abstract

Emergent viruses require effective treatment regimens, and the severe acute respiratory syndrome coronavirus-2 variants are still evolving. Favipiravir has emerged as an effective antiviral medication, especially after its popularity against COVID-2019. Despite its growing popularity, favipiravir has not yet been included in any pharmacopeia, and new dosage forms are being developed to improve its bioavailability for various infections. Therefore, studying its stability and developing methods capable of detecting its impurities and degradation products are essential. An isocratic high-performance liquid chromatography with photodiode array detection method was also designed using the Quality-by-Design approach and validated to determine favipiravir in presence of its hydrolytic degradation products, besides two major manufacturing impurities (namely, 3,6-dichloro pyrazine-2-carbonitrile and 6-fluoro-3-hydroxypyrazine-2-carbonitrile). The separation was achieved using a mobile phase of 25.0 mM phosphate buffer (pH 3.04): acetonitrile (92: 8, v/v) at a 1.0 mL min⁻¹ flow rate. A Hypersil C18-BDS column (5.0 μm, 250.0 × 4.6 mm) was employed at room temperature and detection at 323.0 nm. The method had a linear range (5.0–100.0 µg mL⁻¹) with a limit of detection and quantification of 0.51 and 1.54 µg mL⁻¹. The drug's stability after forced degradation and at different pH levels was explored. Key results proved that FAV is most stable at pH 5.0, with calculated activation energies for the acidic and alkaline degradation processes being 53492.276 and 61896.899 kJ/mole, respectively. Moreover, the analysis of expired favipiravir tablets revealed the presence of the alkaline degradate, thereby demonstrating the efficacy of the method. The proposed method was evaluated for its greenness and blueness to demonstrate its ecological safety and practicality, scoring 0.65 in the Analytical Greenness (AGREE) metric and 85.00 on the Blue Applicability Grade Index (BAGI). It is the first sustainable method developed using the Quality-by-Design to profile favipiravir together with its degradation products and impurities simultaneously.