The coronavirus disease 2019 (COVID-19) pandemic, due to the novel severe acute respiratory
syndrome coronavirus 2 (SARS-CoV-2), emerged in December 2019 and has rapidly
spread globally. As the confirmed number of cases has reached 83 million worldwide, the potential
severity and the deadly complications of the disease requires urgent development of effective drugs
for prevention and treatment. No proven effective treatment for this virus currently exists. Most of
the antiviral discovery efforts are focused on the repurposing of approved or clinical stage drugs.
This review highlights the small-molecule repurposed antiviral agents that are currently under investigation
in clinical trials for COVID-19. These include viral polymerase and protease inhibitors
remdesivir, galidesivir, favipiravir, ribavirin, sofosbuvir, tenofovir/emtricitabine, baloxavir marboxil,
EIDD-2801, lopinavir/ritonavir; virus-/host-directed viral entry and fusion inhibitors arbidol
chloroquine/hydroxychloroquine, chlorpromazine, camostat mesylate, nafamostat mesylate,
bromhexine and agents with diverse/unclear mechanism of actions as oseltamivir, triazavirin,
ivermectin, nitazoxanide, niclosamide and BLD-2660. The published preclinical and clinical data
to date on these drugs as well as the mechanisms of action are reviewed.