  The virus SARS-CoV-2 has created a situation of global emergency all over the
world from the last few months. We are witnessing a helpless situation due to
COVID-19 as no vaccine or drug is effective against the disease. In the present
study, we have tested the applicability of some combination drugs against
COVID-19. We have tried to understand the mechanism of action of some
repurposed drugs: Favipiravir (F), Hydroxychloroquine (H) and Oseltamivir (O).
The ADME analysis have suggested strong inhibitory possibility of F, H, O
combination towards receptor protein of $3CL^{pro}$ of SARS-CoV-2 virus. The
strong binding affinity, number of hydrogen bond interaction between inhibitor,
receptor and lower inhibition constant computed from molecular docking
validated the better complexation possibility of F+H+O: $3CL^{pro}$
combination. Various thermodynamical output from Molecular dynamics (MD)
simulations like potential energy ($E_g$), temperature (T), density, pressure,
SASA energy, interaction energies, Gibbs free energy ($\Delta G_{bind}$) etc.,
also favored the complexation between F+H+O and CoV-2 protease. Our In-Silico
results have recommended the strong candidature of combination drugs
Favipiravir, Hydroxychloroquine and Oseltamivir as a potential lead inhibitor
for targeting SARS-CoV-2 infections.
