**14. Baricitinib**

SARS-CoV-2 penetrates host cells by receptor-mediated endocytosis, just as other viruses. AP2-related protein kinase 1 controls the process of endocytosis (AAK1). As a result, disrupting AAK1 will prevent not just viral entrance but also intracellular viral assembly. Baricitinib is a Janus kinase (JAK) inhibitor that has a high affinity for AAK1 and can inhibit it. SARS-CoV-2 infection can be treated with baricitinib, which inhibits both viral entry and the inflammatory response [106]. JAK inhibitors such as ruxolitinib and fedratinib, which are linked to baricitinib, decreased clathrinmediated endocytosis at higher dosages, suggesting that they may not be effective at acceptable concentrations in lowering viral infectivity. Neutropenia, lymphocytopenia, and viral reactivation have all been linked to the use of baricitinib for therapeutic purposes. Because individuals infected with SARSCoV-2 had a lower absolute lymphocyte count, baricitinib may increase the risk of co-infection [107].

#### **15. Imatinib**

Blocking virus-host fusion is a promising target for the novel antiviral agents that inhibit the Abl kinase pathway [41]. In a study, imatinib, an Abl kinase inhibitor, was observed to block the replication of SARS and MERS viruses by blocking viral fusion in 2016 [108]. COVID-19 utilized the SARS-coronavirus receptor ACE2 as well as the cellular protease TMPRSS2 to get access to target cells; therefore, TMPRSS2, transmembrane serine protease 2, inhibiting medicines such imatinib might be evaluated as COVID-19 disease treatment alternatives [37].

#### **16. Camostat mesylate**

Another possible medicine that targets the fusion stage in viruses is camostat mesylate, a serine protease inhibitor. SARS-CoV-2 enters target host cells via ACE-2 receptors and/or TMPRSS2 receptors, with camostat mesylate acting as a TMPRSS2 inhibitor. It inhibits the virus's cellular entrance by downregulating the production of the SARS-CoV-2 spike (S) protein, which prevents surface fusion. SARS-CoV infection in human bronchial epithelial cells was inhibited by camostat mesylate [109]. In vitro testing

revealed that camostat mesylate and E-64d (a cysteine protease inhibitor) effectively blocked SARS-CoV-2 TMPRSS2 binding. Clinical studies are now underway to compare the efficacy of hydroxychloroquine and camostat mesylate vs. hydroxychloroquine alone. Another serine protease inhibitor, nafamostat mesylate, was shown to be 15 times more effective in preventing the SARS-CoV-2 virus from infecting host cells. As a result, nafamostat mesylate can be regarded a preferable option to camostat mesylate due to its more robust antiviral activity and acceptable safety profile [37]. Disseminated

**Figure 3.** *Chemical structure of antiviral drugs.*

intravascular coagulation is also treated with nafamostat mesylate (DIC). It will aid in the management of DIC, as seen by increased fibrinolysis in COVID-19 patients [110].

#### **16.1 Nitazoxanide**

In an in vitro research utilizing Vero E6 cells, nitazoxanide and its active component, tizoxanide, showed promise against MERS CoV and SARS CoV-2, with EC50 values of 0.92 and 2.12 μM, respectively [111]. In addition to coronaviruses, it exhibited action against norovirus, rotavirus, parainfluenza, respiratory syncytial virus, and influenza virus. This antiviral efficacy is due to the fact that the action mechanism is based on interfering with the virus's host-regulated reproduction pathways rather than the virus's particular pathways [112]. Nitazoxanide stimulates innate antiviral systems through amplification of cytoplasmic RNA sensing and type 1 IFN pathways. Nitazoxanide increases the expression of certain host systems that interfere with viral infection, allowing viruses to evade the host's cellular defenses [113]. The nitazoxanide used against influenza viruses blocks the maturation of viral hemagglutinin at the post-translational stage [112]. Even if the findings aren't promising, this medicine is used to treat some acute respiratory infections such as influenza. Although the in vitro activity of nitazoxanide against SARS-CoV-2 is promising, additional research is needed to understand its function in the management of COVID-19 (**Figure 3**).

#### **16.2 Other antiviral drugs**

Other various antiviral agents have been utilized to determine their impacts against SARS-CoV-2. Galidesivir is a nucleoside analog and a protease inhibitor [114]. This drug mechanism on COVID-19 is hypothesized to be similar to other antivirals, although its exact action mechanism is unknown. Another antiviral agent for COVID-19 is Tenofovir, which is known as an anti-influenza drug. It is an antiretroviral agent that targets DNA polymerase and inhibits virus replication [115, 116]. The action mechanism of this substance against COVID-19 requires further studies.
