2. Clinical evidence of antiviral agents
A large number of antiviral agents, many of which are used for the treatment of other diseases, are currently undervaluation for COVID-19. The figure 2 shows the main drugs evaluated for COVID-19 and their mechanisms of action. We reported below those for which clinical evidence on their safety and efficacy is available.
Remdesivir is an antiviral drug effective against a broad spectrum of RNA viruses (including MERS-CoV and and SARS-CoV) (Agostini et al., 2018; de Wit et al., 2020; Sheahan et al., 2020). It is a nucleotide analogue that inhibits the RNA-dependent RNA polymerase (RdRp) essential for viral replication. A randomised, double-blind, placebo-controlled, multicenter trial, conducted on adults (aged ≥18 years) admitted to hospital with laboratory-confirmed SARS-CoV-2 infection, showed no difference for the time to clinical improvement between the remdesivir group and the placebo group (Wang et al., 2020b). A randomized, open-label trial, evaluating the efficacy of 5 or 10 days of remdesivir treatment compared to the standard care in hospitalized patients with confirmed severe acute respiratory syndrome and moderate COVID-19 pneumonia (pulmonary infiltrates and room-air oxygen saturation >94%), showed that patients treated with 10-day course of remdesivir had no statistically significant difference in clinical status (at 11 days) compared to standard care. On the contrary, those treated with 5-day course of remdesivir had a statistically significant difference in clinical status, but the difference was defined as uncertain for clinical importance (Spinner et al., 2020). A double-blind, randomized, placebo-controlled trial (NIAID-ACTT-1) of intravenous remdesivir administered to adults hospitalized for COVID-19 showed that remdesivir was superior to placebo in shortening the time to recovery. Specifically, patients receiving remdesivir had a median recovery time of 10 days (95% confidence interval [CI], 9 to 11) compared with 15 days of patients receiving placebo (95% CI, 13 to 18) (Beigel et al., 2020). Finally, a randomized, open-label, phase 3 trial on hospitalized patients with severe COVID-19 not requiring mechanical ventilation, which were randomized to receive intravenous remdesivir for 5 or 10 days, showed no difference in terms of clinical status between the two groups (Goldman et al., 2020). A meta-analysis of aforementioned clinical trials showed that the treatment with remdesivir for 10 days increased the recovery rate at day 14 in severe COVID-19 patients (RR=1.5, 95%CI 1.33-1.7) and at day 28 in moderate and severe COVID-19 patients (RR=1.14, 95%CI 1.06-1.22). Additionally, in all patients, remdesivir decreased the mortality rate at day 14, but not at day 28. The best response to remdesivir for both recovery and mortality rates was observed in nonmechanically ventilated COVID‐19 patients at day 14 (Elsawah et al., 2020). Among observational data, a study conducted on patients under mechanical ventilation with confirmed COVID-19 showed a significant beneficial effect of remdesivir on survival (Pasquini et al., 2020). Moreover, a clinical improvement was also observed in hospitalized patients with severe COVID-19 who were treated with compassionate-use remdesivir (Grein et al., 2020). Based on the results of the NIAID-ACTT-1 trial, the European Medicine Agency (EMA) has granted a conditional marketing authorisation to remdesivir (Veklury©) for the treatment of adults and adolescents from 12 years of age with COVID-19 pneumonia who require supplemental oxygen. Remdesivir is the first medicine that was recommended for COVID-19 in Europe with data evaluated in a short timeframe through a rolling review procedure, which is an approach used during public health emergencies to rapidly evaluate data. However, on November 20th, 2020 the World Health Organization (WHO) has issued a conditional recommendation against the use of remdesivir in hospitalized patients with COVID-19, regardless of disease severity, as there is no evidence demonstrating an improvement of survival or other outcomes during its use in these patients. This recommendation is based on the interim results of the open-label WHO Solidarity Trial and from data of 3 other randomized controlled trials, considering data from over 7000 patients across the 4 trials (World Health Organization). Currently, the Committee for Medicinal Products for Human Use (CHMP) of EMA is evaluating data on mortality at day 28 derived from the NIAID-ACTT-1 trial. Moreover, the EMA has requested the full Solidarity data from WHO and the marketing authorisation holder in order to assess, together with any other relevant available data, if any changes are needed to the marketing authorisation of remdesivir. In terms of safety, the EMA is also evaluating a signal for kidney toxicity, a condition that could have other causes in COVID-19 patients (European Medicine Agency).Lopinavir/ritonavir is a combination composed by lopinavir, a protease inhibitor with high specificity for HIV-1 and HIV-2, and ritonavir, an inhibitor of cytochrome P450 that allows to increase lopinavir plasma concentration (Scavone et al., 2020). First results from a randomized trials conducted in patients with SARS-CoV-2 infection did not show any benefit for this combination compared to the standard care alone (Cao et al., 2020; Li et al., 2020d), even though the triple antiviral therapy (lopinavir/ritonavir, ribavirin, and interferon beta-1b) was safer and more effective than lopinavir/ritonavir alone (Hung et al., 2020).In addition, the RECOVERY trial that aimed to compare a range of possible treatments with usual care in patients hospitalized for COVID-19 showed no reductions in 28-day mortality, duration of hospital stay, or risk of progressing to invasive mechanical ventilation or death for the lopinavir/ritonavir group (Horby et al., 2020b). A recent meta-analysis, comparing the treatment with lopinavir/ritonavir with the standard of care/control or any other antiviral agent/combinations, showed no difference between the lopinavir/ritonavir combination and the standard of care in terms of progression to more severe state, mortality, and virological cure on days 7-10. Moreover, no difference in efficacy was observed with lopinavir/ritonavir compared to umifenovir or hydroxychloroquine (Bhattacharyya et al., 2020). Another meta-analysis demonstrated no significant difference in terms of negative polymerase chain reaction (PCR) results between patients treated with lopinavir/ritonavir and those treated with the standard care (Wang et al., 2020a). Data from observational studies revealed no differences between lopinavir/ritonavir and hydroxychloroquine administered in patients with severe or mild-moderate COVID-19 (Choi et al., 2020; Karolyi et al., 2020; Lecronier et al., 2020). A retrospective study, conducted instead in non-severe patients with COVID-19, also showed no improvement in the prognosis or shortening of clinical course with lopinavir/ritonavir treatment (Gao et al., 2020). On the contrary, a retrospective cohort study showed that the combined antiviral therapy (lopinavir/ritonavir plus umifenovir) is more effective than lopinavir/ritonavir monotherapy (Deng et al., 2020). Based on the available evidence, the regular use of lopinavir/ritonavir in the treatment of COVID-19 cannot be supported. Some evidences suggest its use as a combination therapy but further clinical trials are needed to evaluate lopinavir/ritonavir’s efficacy and safety in COVID-19 patients.
Favipiravir is a drug authorized for the treatment of influenza virus infections in Japan. It is a prodrug converted by intracellular phosphoribosylation into the active form able to inhibit the RdRp. Preliminary data suggested its safety and efficacy in shortening the time to recovery and in reducing pneumonia symptoms (Scavone et al., 2020; WATANABE et al., 2020). A randomized clinical trial, comparing the efficacy and safety of favipiravir vs umifenovir in hospitalized patients with COVID-19, demonstrated a higher efficacy for favipiravir than umifenovir (p= 0.01). Regarding adverse events, liver enzyme abnormalities, psychiatric disorders, gastrointestinal symptoms, and serum uric acid elevations were those most commonly reported (Chen et al., 2020a). An open-label study, evaluating the effects of favipiravir versus lopinavir/ritonavir in patients with COVID-19 who were also treated with aerosol inhalation of interferon (IFN)-α, showed a faster viral clearance and a better chest computed tomography change for the favipiravir group. Additionally, fewer adverse events were observed in the favipiravir group than lopinavir/ritonavir group (Cai et al., 2020). On the contrary, the combination favipiravir and inhaled IFN beta-1b showed no difference for inflammatory biomarkers at hospital discharge and for the overall length of hospital stay when compared to hydroxychloroquine(Khamis et al., 2020). Another study, aiming to evaluate the clinical outcomes and plasma concentrations of baloxavir marboxil and favipiravir in COVID-19 patients, failed in demonstrating a virological effect and clinical benefits of these two drugs. Authors concluded that this result could be determined by the insufficient concentrations of these drugs relative to their antiviral activities (Lou et al., 2020). An adaptive, multicenter, open label, randomized, phase II/III clinical trial of favipiravir versus standard of care in hospitalized patients with moderate COVID-19 pneumonia demonstrated a rapid antiviral response with favipiravir (Ivashchenko et al., 2020). Based on these preliminary results, the Russian Ministry of Health granted, in May 2020, a fast-track marketing authorization to favipiravir for the treatment of COVID-19 patients. A meta-analysis of some aforementioned clinical trials showed a significant clinical and radiological improvement with favipiravir compared to the standard of care, but no significant difference with regards to viral clearance, oxygen support requirement, or side effects (Shrestha et al., 2020). Currently, two clinical trials are ongoing to evaluate the efficacy and safety of favipiravir alone (NCT04336904) or in combination with tocilizumab (NCT04310228) for the treatment of COVID-19. The promising effectiveness of favipiravir for COVID−19 was also showed in a retrospective observational study (Rattanaumpawan et al., 2020). Based on the available evidence, favipiravir is effective in alleviate symptoms and in the clinical improvement of COVID-19 patients but further studies are need to prove its benefit in terms of viral clearance, oxygen support requirement, and mortality.Darunavir/cobicistat is another agent considered as a potential treatment for SARS-CoV-2 infection. Darunavir is an inhibitor of dimerization and of the HIV-1 protease, while cobicistat is an inhibitor of cytochromes P450 that increases darunavir plasma concentration (Deeks, 2018). Today, there are conflicting in vitro data on the effect of darunavir in inhibiting SARS-CoV-2 viral replication (Alshaeri and Natto, 2020; De Meyer et al., 2020). Results from a single-center, randomized, and open-label trial of darunavir/cobicistat plus interferon alpha 2b vs interferon alpha 2b alone in COVID-19 patients showed no difference in the proportion of negative PCR results at day 7 between the two groups (Chen et al., 2020b). Nicolini et al reported the results on the real-life use of darunavir/cobicistat in severe COVID-19 patients. Their findings showed that, although well tolerated, this treatment did not reduce mortality in COVID-19 (Nicolini et al., 2020). On the contrary, a case-control study showed a lower mortality for darunavir/cobicistat group than the control group (Odds Ratio, OR 0.07, 95%CI 0.01-0.52, p=0.009) in critically ill patients with SARS-CoV-2 infection (Kim et al., 2020).Triazavirin , a guanosine nucleotide analogue that inhibits RNA synthesis, was compared to placebo in a pilot randomized controlled trial for the treatment of COVID-19. This study found no difference in the time to clinical improvement between groups in spite of a less frequent use of concomitant therapies for respiratory, cardiac, renal, hepatic, or coagulation supports in the triazavirin group (Wu et al., 2020). Currently, a randomized, phase 2/3 clinical trial is evaluating the effects of triazavirin vs. placebo in inpatients with mild-moderate COVID-19 (the study will end at December 31, 2021) (NCT04581915).Umifenovir is a membrane hemagglutinin fusion inhibitor that blocks the attachment of viral envelope protein to host cells (Liu et al., 2020a). As mentioned above, some clinical trials failed to prove a clinical benefit with umifenovir compared to supportive care (Li et al., 2020d) or favipiravir (Chen et al., 2020a) in COVID-19 patients. However, an observational study suggested its superiority to lopinavir/ritonavir in shortening the duration of positive RNA in COVID-19 patients (Zhu et al., 2020). Clinical trials are ongoing to evaluate the efficacy and safety of umifenovir (NCT04260594) or umifenovir, oseltamivir, and lopinavir/ritonavir (NCT04255017) for the treatment of COVID-19.Danoprevir is a hepatitis C virus NS3 protease inhibitor that was firstly evaluated compared to lopinavir/ritonavir in COVID-19 patients. The study found that the group treated with danoprevir had a shorter mean time to achieve both negative nucleic acid testing and hospital stays than lopinavir/ritonavir group (Zhang et al., 2020c). Two clinical trials are ongoing to evaluate the efficacy and safety of danoprevir in combination with ritonavir (NCT04345276) or ritonavir plus interferon (NCT04291729).Sofosbuvir and daclatasvir are direct-acting antivirals that represent potential candidates for the treatment of COVID-19. A trial, evaluating the effectiveness of sofosbuvir and daclatasvir compared to ribavirin in patients with severe COVID-19, showed a relative risk of death of 0.17 (95% CI 0.04-0.73, P = 0.02) for the sofosbuvir/daclatasvir group (Eslami et al., 2020). Similarly, an open-label, multicentre, randomized controlled clinical trial conducted in adults with moderate or severe COVID-19 showed that the group treated with sofosbuvir/daclatasvir plus standard care had a significant reduction of the duration of hospital stay compared with standard care alone (Sadeghi et al., 2020). A single-centre, randomized, controlled trial of adults with moderate COVID-19, comparing the treatment with sofosbuvir, daclatasvir, and ribavirin to the standard care, demonstrated instead no difference in terms of median duration of hospital stay, number of Intensive care Unit (ICU) admissions, and the number of deaths between groups, but the cumulative incidence of recovery was higher in the sofosbuvir/daclatasvir/ribavirin group (Abbaspour Kasgari et al., 2020). All studies highlight the need of further investigations in larger clinical trials.Nafamostat and camostat mesilate are inhibitors of TMPRSS211, a protease fundamental for the penetration of coronaviruses into the cell (Mascolo et al., 2020). First evidence showed a clinical improvement with the use of nafamostat and hydroxychloroquine, or nafamostat and favipiravir in severe COVID-19 patients (Doi et al., 2020; Iwasaka et al., 2020). Moreover, nafamostat was also effective in three cases of elderly patients with COVID-19 pneumonia. Both drugs are currently undervaluation in different clinical trials (www.clinicaltrials.gov).Ivermectin , a drug used for parasite infestations, has the ability to reduce, in vitro, the viral RNA of SARS-CoV-2 (Caly et al., 2020). Today, clinical observational data on the use of this medicine are conflicting. The ICON study, a chart review of consecutive patients hospitalized with confirmed COVID-19 treated with or without ivermectin (200 μg/kg at day 1 and at the discretion of the physician at day 7), showed a lower mortality in the ivermectin group, but no difference was found for the extubation rates or length of stay (Rajter et al., 2020). Another retrospective study conducted in hospitalized patients with COVID showed that a single dose of ivermectin (200 μg/kg) did not improve clinical and microbiological outcomes of patients with severe COVID-19. However, as Authors stated, the drug was given at late stages of infection (median 12 days after the start of symptoms) and at a standard single dose that could be lower than the half maximal inhibitory concentration (IC50) needed for SARS-CoV-2 infection (Camprubí et al., 2020). Ivermectin is also undervaluation in different clinical trials (www.clinicaltrials.gov). Preliminary results from a randomized, controlled, phase 3, clinical trials, evaluating the recovery from COVID-19, showed the efficacy of the combination ivermectin and doxycycline compared to placebo (NCT04523831). Finally, monoclonal antibodies (figure 2), such as meplazumab ,REGN-COV2 , and bamlanivimab , have been developed to prevent the viral attachment of SARS-CoV-2 to host cells.
Meplazumab is listed among antiviral agents because, based on its mechanism of action, it can control the virus replication. In fact, it is an inhibitor of CD147, a glycoprotein involved in the viral entry of SARS-CoV-2 by interacting with the coronavirus S protein. CD147 also has a pro-inflammatory activity and regulates cytokine secretion and leukocytes chemotaxis during viral infections. Preliminary results showed that meplazumab compared to the control group was associated with a faster improvement of pneumonia (Bian et al., 2020). Two clinical trials are ongoing to evaluate the safety and efficacy of meplazumab in patients with COVID-19 (NCT04275245, NCT04586153).REGN-COV2 is a cocktail of two potent monoclonal antibodies (casirivimab and imdevimab) targeting the spike protein of SARS-CoV-2. First descriptive data showed that REGN-COV2 is able to reduce the viral load and the time to alleviate symptoms in non-hospitalized patients with COVID-19. Moreover, REGN-COV2 also showed positive trends in reducing medical visits (Regeneron Pharmaceuticals). Clinical trials are currently ongoing to evaluate its efficacy and safety for the treatment (NCT04425629, NCT04426695, NCT04381936) or prevention (NCT04452318) of COVID-19, and a clinical trial is ongoing to assess its safety, tolerability, pharmacokinetics, and immunogenicity in healthy adult volunteers (NCT04519437). On November 21st, 2020 The U.S. Food and Drug Administration (FDA) granted an emergency authorization for casirivimab and imdevimab for the treatment of mild to moderate COVID-19 in adults and paediatric patients (≥ 12 years and weighing at least 40 Kg) with positive results of direct SARS-CoV-2 viral testing and who are at high risk for progressing to severe COVID-19. This approval based on data from a clinical trial demonstrating a reduction of COVID-19-related hospitalization or emergency room visits within 28 days after treatment in patients at high risk for disease progression (Food and Drug Administration).Bamlanivimab is a recombinant, human IgG1 monoclonal antibody (mAb) directed against the spike protein of SARS-CoV-2. Recently, a Phase 1 study of bamlanivimab in hospitalized patients with COVID-19 was successfully completed (NCT04411628) (Eli Lilly and Company), and an interim analysis of an ongoing phase 2 clinical trial in outpatients with recently diagnosed mild or moderate COVID-19 (BLAZE-1, NCT04427501) showed that one of three doses of bamlanivimab accelerates the natural decline in viral load over time (Chen et al., 2020c). Moreover, bamlanivimab has demonstrated to reduce hospitalizations and symptoms compared to placebo, with the most pronounced effects observed in high-risk patients (Chen et al., 2020c). Based on these results, on November 9th, 2020 bamlanivimab was authorized by the U.S. FDA, as emergency use, for the treatment of mild to moderate COVID-19 in adults and paediatric patients (≥ 12 years), who are at high risk for progressing to severe COVID-19 or hospitalization. Bamlanivimab is recommended to be administered as soon as possible after a positive COVID-19 test and within 10 days of symptom onset (Eli Lilly and Company). Currently, bamlanivimab is being evaluated in a phase 3 clinical trial assessing the prevention of COVID-19 in residents and staff at long-term care facilities (BLAZE-2, NCT04497987), and in the National Institutes of Health-led ACTIV-2 study in ambulatory COVID-19 patients (Eli Lilly and Company). Both bamlanivimab and REGN-COV2 are not authorized for use in hospitalized patients or in patients requiring oxygen therapy due to COVID-19 as they resulted most effective when given to a patient shortly after diagnosis, and in patients who have high viral load or who have not yet mounted their own immune response. Other drugs potential therapeutics candidates for COVID-19, not mentioned above, for which we have less evidence are: azidovudine, galidesivir, tenofovir, lepidasvir, velpatasvir (Alshaeri and Natto, 2020; Scavone et al., 2020). In conclusion, the role of antiviral agents for COVID-19 is still being investigated and the few data available does not allow making any conclusion. Remdesivir is the only one recommended in Europe for COVID-19 but it was also recently questioned for efficacy and safety and it is currently undervaluation by the EMA. Regarding monoclonal antibodies, such as bamlanivimab, which is indicated in patients at high risk of hospitalization, a question should be raised: “how to define who might be at risk of hospitalization, since individuals who go to hospital are frequently difficult to predict?”. Moreover, the place in therapy of bamlanivimab and REGN-COV2 is tricky too; it would be interesting to understand which type of patients would benefit from these therapies.
Lastly, a new monoclonal antibody is currently under early stage of development in Italy at the MAD (Monoclonal Antibody Discovery) Lab of the Fondazione Toscana Life Sciences. This investigational therapy was obtained starting from convalescent plasma. At this moment, researchers found that the antibody is able to bind the spike protein and disable the virus. Thus, this therapy could serve both to prevent and treat Covid-19 (The Florentine, 2020).