Drug Analysis of Favipiravir for COVID-19 Treatment Based on Lipinski's Rule of Five: Application of Quantum Mechanics in Drug Design

Abstract

Favipiravir a pyrazine carboxamide derivative, is an antiviral agent that specifically inhibits RNA-dependent RNA polymerase (RdRp), essential for viral replication. Its molecular structure, characterized by the presence of amine (NH₂), carbonyl (C=O), and fluorine (F) functional groups, significantly influences its biological activity. Favipiravir meets most of Lipinski's Rule of Five criteria, including a molecular weight of 157.1 g/mol (<500), an optimal log P value, two hydrogen bond donors, and an appropriate number of hydrogen bond acceptors, indicating its potential as an orally bioavailable drug. The carbonyl group plays a crucial role in forming hydrogen bonds with active residues of RdRp, while the fluorine group enhances the molecule's lipophilicity, facilitating membrane penetration. Quantum mechanical analysis, such as Density Functional Theory (DFT), highlights Favipiravir's optimal HOMO-LUMO energy gap, suggesting favorable chemical reactivity and stability in physiological conditions. Clinically, Favipiravir has demonstrated effectiveness in accelerating RT-PCR negative conversion in mild-to-moderate COVID-19 cases, shortening recovery times for symptoms like fever and cough. Its efficacy in severe cases requires further investigation. Structural challenges, including low bioavailability under extreme pH and limited metabolic stability, remain critical issues. Structural optimization via quantum mechanical approaches may enhance stability, improve RdRp affinity, and minimize side effects, enabling the development of better analogs for therapeutic use.