Table 2. Mechanism of Action of Drug Candidates on SARS-CoV-2 Infection.

Drugs	Types	Mechanism of action
Chloroquine and hydroxychloroquine	4-aminoquinoline	The post-translation alteration of newly synthesized proteins via glycosylation inhibition [52].
Lopinavir/ritonavir	Protease inhibitors	Blocks viral cellular entry [53].
Umifenovir	Fusion inhibitor	Viral fusion inhibition with the targeted membrane, which blocks virus entry into the cell [54].
Favipiravir	RNA polymerase inhibitors	Favipiravir is a prodrug that is ribosylated and phosphorylated intracellularly to form the active metabolite favipiravir ibofuranosyl-5’-triphosphate (T-705-RTP). T-705-RTP competes with purine nucleosides and interferes with viral replication by incorporation into the virus RNA and thus, potentially inhibiting the RNA-dependent RNA polymerase (RdRP) of RNA viruses [31].
Methylprednisolone	Corticosteroids	Prolongs the survival time and prevents complication of clinical cases through its anti-inflammatory and immunomodulatory action [55].
Thalidomide	Immunomodulators	It has an anti-inflammatory action due to its ability to speed up the degradation of messenger RNA in blood cells and thus reduce tumor necrosis factor-α (TNF-α). Furthermore, thalidomide can increase the secretion of interleukins (IL), such as IL-12, and activate natural killer cells [56].
Remdesivir	Adenosine nucleotide analogues	Remdesivir’s ability is to metabolize into an active form known as GS-441524 which is an adenosine nucleotide analog. The GS-441524 interferes with the action of viral RdRP and evades proofreading by viral exoribonuclease (ExoN). This decreases viral RNA production [37].
Interferon	Low molecular weight protein	The expression of the interferon-stimulated genes (ISGs) is induced by interferon, in the infected as well as in neighboring cells. These lead to development of an antiviral environment, thus inhibiting further viral replication. The interferons augment the immune system in various ways, resulting in different antiviral, antiproliferative and immunomodulatory activities [48-50].

SARS-CoV-2: severe acute respiratory syndrome coronavirus 2.