Remdesivir, depicted in
Figure 6, stands as the first authorized drug specifically developed for the treatment of Ebola. [
176,
197] Ebola, being a single-strand RNA virus, faces inhibition from Remdesivir, which acts as an adenosine analogue. This inhibition targets the viral RNA-dependent RNA polymerase (RdRp), leading to either premature or delayed RNA chain termination. [
20,
177,
178,
179] Notably, Remdesivir has demonstrated antiviral activity against respiratory viral infections, including SARS-CoV-2, in in vitro settings. [
180] In vivo experiments involving SARS-CoV and MERS-CoV-infected animals revealed reduced airway inflammation and improved lung function, showcasing similar protective effects. The efficacy of post-exposure therapy is contingent on the timing of Remdesivir administration. [
20] Furthermore, the licensing of nucleoside analogues for treating both DNA and RNA viruses is crucial in comprehending the mechanism of action underlying Remdesivir. However, several nucleoside analogue inhibitors have been observed to be ineffective against CoVs. [
181,
182] Remdesivir, a nucleoside analogue, works as an RdRp inhibitor by concentrating on the viral genome involved in viral replication. In the RdRp process, it thereby inhibits the protein complex of CoVs. The host breaks down Remdesivir to its active metabolite nortriptyline (NTP), which is then conjugated to ATP and incorporated into the developing RNA strand. Inclusion of a new strand stops the RNA synthesis and the expansion of the RNA strand once nucleotides are added. All CoVs include a proofreading process that detects and removes other nucleoside analoge activity, keeping antiviral activity. Surprisingly, it has been discovered that the mutant Murine hepatitis virus (MHV) lacked proofreading capabilities and was hence highly vulnerable to Remdesivir. It is also likely that mutations that enhance proofreading or base-pairing precision will result in Remdesivir resistance. Some data suggested that Remdesivir might work via a different mechanism, permitting partial antiviral vitality to endure despite viral changes. [
182] WHO has authorized/approved the emergency use of Remdesivir. WHO revised its conditional advice against Remdesivir in hospitalised patients in November 2020 and is not recommended in this situation under any circumstances. [
183] Phase III clinical research on Remdesivir is crucial for obtaining the more potent antiviral drug to combat this outbreak. [
184] Clinical trials in 36 of 53 patients show appropriate data in 61 hospitalised patients taking Remdesivir off-label. However, without a placebo group, these findings are difficult to comprehend. An initial randomised controlled trial was flawed, favouring Remdesivir with a non-significant trend toward shorter time to clinical changes. This trial was insufficient, however it did show that patients treated with Remdesivir had better healing as an average recovery time of 11 days vs. placebo of 15 days. In addition, there were improvements for better survival on day 14. The research indicated disadvantages in individuals with high-flow oxygen, and invasive or non-invasive ventilation, indicating that antivirals like Remdesivir might have a poor impact in late diseases where the phenotype is likely to be inflammatory. The analysis was published before the full results could be obtained via follow-up research. [
20] Remdesivir is now the subject of several clinical research studies regarding COVID-19 prevention. An initial dose of 200 mg of intravenous Remdesivir is given to participants in this double-blinded, placebo-controlled study on the first day, followed by a controlled dose of 100 mg per day and up to a maximum of 10 cumulative days of treatment before release. The initial trial result is expressed as the percentage of patients in each group, employing a seven-category clinical severity scale, up to the fifteenth day following the initiation of therapy, as indicated by the United States National Library of Medicine clinical trials registry.Gilead Sciences is also supporting a Remdesivir study in patients with severe COVID-19 that will combine a primary outcome test of fever with an outcome test of oxygen normalization. In Hubei Province, China, two double-blind placebo-controlled trials included patients: one for hospitalized individuals with mild-to-moderate COVID-19 and the other for severe cases. [
178] In the mild-to-moderate study, key success criteria include the normalization of body temperature, oxygen consumption, breathing rate, and cough recovery for a minimum of 72 hours. Timing for health advancement is the key outcome in the extreme case study, which is presented using a six-category ratio scale from discharge to fatality. [
178] It is described that Remdesivir was also found to be effective against MERS-CoV, reducing viral loads in the infected mice and restoring normal lung-based function. [
185] Additionally, it is regarded as a treatment-assist agent for SARS-CoV-2. [
176] The viral load in oropharyngeal and nasopharyngeal swabs could be reduced by Remdesivir treatment for about 12 days, according to preliminary studies. [
87] The combination of Chloroquine, an anti-malarial drug, and Remdesivir, can successfully stop the growth of SARS-CoV-2 in Vero E6.86 cell lines in an in vitro studies. The potential effect of Remdesivir in COVID-19 is being studied in clinical trials in France, USA, and Norway. Remdesivir was used in treatment in Singapore and the USA and injected intravenously into the first patient who recovered there. [
186] In a different research, 584 participants received Remdesivir or continued receiving conventional therapy, and 533 (91%) of these patients finished the experiment. Patients in the 5-day Remdesivir group received an average of 5 days of treatment, while those in the 10-day Remdesivir group received an average of 6 days. Compared to patients getting standard therapy, patients in the 5-day Remdesivir group showed statistically noticeably higher probabilities of a better clinical status distribution on day 11. [
187] However, trial outcomes regarding safety, secondary outcomes, and viral load showed 22 of 158 Remdesivir patients died (14%), compared to ten of 78 placebo patients (13%), and there was no evidence that viral load declined differently over time in the placebo groups and Remdesivir. [
188] Remdesivir's limited oral bioavailability often limits its preventive use. Additional pharmacological measures are required to make the drug available to the outpatient population. Remdesivir inhalation Phase 1 trial and FDA approval were recently reported by the manufacturer. [
189] During clinical trials, Remdesivir was administered as a freeze-dried powder injection. The dosage technique employed is as follow; on the first day, an initial dose of 200 mg of Remdesivir is supplied via intravenous dripping. Then, for the next 9 days, 100 mg is supplied intravenously as a maintenance dose. [
129]