On the basis of the systematic review of published evidence, the different pharmacological interventions explored for the therapeutic management of patients with COVID–19 were chloroquine/hydroxychloroquine, remdesivir, arbidol, lopinavir, ritonavir, glucocorticoids, immune modulators, immunoglobulin/plasma therapy, tissue plasminogen activator, recombinant erythropoietin, tocilizumab, baricitinib, ivermectin, tetracyclines, statins, homoharringtonine, and metronidazole. All the drugs that have been explored as therapeutic options were previously used for the treatment of other clinical conditions. Hence, the evidence base does not follow the conventional preclinical-early clinical (phases I and II)-phase III studies. But, on the contrary, the drugs are repurposed and the main aims of later-stage clinical trials are to reposition the drug for COVID–19 (repositioning clinical trials) .
Chloroquine and Hydroxychloroquine:
Chloroquine is a 9-aminoquinoline, which is a weak base and facilitates antimicrobial effect by increasing the pH of acidic vesicles. It has been safely used for the treatment of malaria, amoebiasis, Human Immune Virus, and autoimmune diseases . The first evidence of its activity against CoV was provided by Vincent et al. in Vero E6 cells against SARS-CoV. They confirmed the prophylactic effect of chloroquine in Vero E6 cells that were pretreated with 10 μM of chloroquine, which reduced the infectivity by 100% in comparison with the control. Similarly, the addition of 0.1 to 1 μM of chloroquine after infection reduced the infection by 50%, suggesting the probable therapeutic effect of chloroquine in SARS-CoV infection . The anti-SARS-CoV–2 activity of chloroquine was assessed by Wang et al. in Vero E6 cell line. The time-of-addition assay suggested a probable role of chloroquine at the entry and post-entry stages of SARS-CoV–2 infection. The effective concentration (EC90) was found to be 6.90 μM, which is clinically achievable with the administration of 500-mg chloroquine . In further physiologically based pharmacokineticmodeling studies, hydroxychloroquine, which is an analog of chloroquine, was found to be more potent than chloroquine with better safety profile .
The first clinical evidence of efficacy was reported by Gautret et al. from a cohort of French patients who were treated with 600 mg of hydroxychloroquine. The study included 42 patients (26 patients treated with hydroxychloroquine and 16 patients in the control group) who were confirmed to be positive for SARS-CoV–2 by RT-PCR. Of the 20 patients treated with hydroxychloroquine available for efficacy assessment, 14 (70%) patients experienced virological cure after 6 days of treatment, whereas only 2 (12.5%) patients in the control group were negative for SARS-CoV–2 after 6 days of treatment. A subgroup of patients in the hydroxychloroquine group were also treated with azithromycin (6 patients), and all of them experienced virological cure, suggesting a better efficacy for hydroxychloroquine in combination with azithromycin than hydroxychloroquine alone (100% vs. 57%, respectively) .
The first evidence of the efficacy of hydroxychloroquine from an RCT was published recently in the preprint server MedRxiv. The study recruited 62 patients positive for SARS-CoV–2 and randomly divided them into the test (hydroxychloroquine) and control (placebo) groups. Comparison of radiologic findings revealed that 61.3% of the patients in the hydroxychloroquine group showed significant improvement, whereas only 16.1% of those in the control group had significant improvement. The body temperature recovery time was also significantly reduced in the hydroxychloroquine group (2.2 [0.4] days) in comparison with the control group (3.2 [1.3] days). Similarly, cough remission time was also significantly reduced in the hydroxychloroquine group .
The efficacy of hydroxychloroquine in combination with azithromycin was also reported in a retrospective study involving French patients. A total of 1061 SARS-CoV–2-positive patients treated with hydroxychloroquine (200 mg 3 times a day) in combination with azithromycin were included in the study (500 mg on day 1 followed by 250 mg daily for the next 4 days). Virological cure and clinical outcomes were assessed. Approximately 92% of the patients experienced virological cure (viral culture and RT-PCR) and 95% of the patients reported alleviation of clinical symptoms. Multivariate analysis revealed older age (Odds ratio (OR): 1.11, 95% confidence interval (CI) 1.07 to 1.15), selective beta-blocking agents (OR: 4.16, 95% CI 1.19 to 14.55), angiotensin II receptor blockers (OR: 18.40, 95% CI 6.28 to 53.90), and medium and high National Early Warning Score (NEWS; OR: 9.48, 95% CI 3.25 to 27.66; OR = 10.05, 95% CI 3.16 to 32.02, respectively) were significantly associated with poor clinical outcome. Cardiac toxicity was not reported in the study . Although cardiac toxicity was not reported in any of the studies, a study by Chorin et al. reported an extension in QT interval in SARS-CoV–2-positive patients treated with hydroxychloroquine, suggesting a risk of arrhythmia .
Despite the positive results favoring the usage of hydroxychloroquine with and without azithromycin in SARS-CoV–2-positive patients, a prospectively randomized study by Jun et al reported a lack of significantly different virological cure rates in patients treated with hydroxychloroquine in comparison with placebo. Other clinical end points such as time to body temperature normalization was also similar among the groups . In another prospective single-arm study conducted by Molina et al., 11 consecutive SARS-CoV–2-positive patients treated with hydroxychloroquine were followed up for the assessment of virological and clinical outcomes. After 6 days of treatment, 80% of the patients remained virologically positive for SARS-CoV–2 by qualitative PCR, which was in contrast to the earlier studies (18, 22). This was further reiterated in a recent study with a propensity-score-matched cohort of patients treated with either hydroxychloroquine alone or in combination with azithromycin or placebo. The rates of death were lower in those treated with placebo (11.4%) compared with those treated with hydroxychloroquine alone (27.8%) and those treated with hydroxychloroquine and azithromycin (22.1%). The risk of ventilation was similar in all the groups. Virological cure and improvement in clinical outcomes were not assessed in this study .
In a recent RCT, the efficacy of hydroxychloroquine was compared with standard of care. The study recruited 150 patients confirmed to be positive for SARS-CoV–2 and randomly treated with hydroxychloroquine plus standard of care (75 patients) and standard of care alone (75 patients). The primary end point was virological cure after 28 days of treatment. Virological cure probability by 28 days in hydroxychloroquine plus standard of care was 85.4% (95% confidence interval [CI], 73.8% to 93.8%), which was similar to that in the standard-of-care alone group (81.3%; 95% CI, 71.2% to 89.6%) . A summary of the available evidences for hydroxychloroquine is provided in (Table 1).
Currently available early clinical evidence provides contradictory findings on the efficacy of hydroxychloroquine in SARS-CoV–2 positive patients. There are currently 125 clinical trials registered in the WHO International Clinical Trials Registry Platform (ICTRP; https://clinicaltrials.gov/ct2/who_table) and 192 studies registered in clinicaltrials.gov. The results of the ongoing studies will provide conclusive evidence on the efficacy of hydroxychloroquine in the treatment of SARS-CoV–2.
Remdesivir is a nucleoside analog with proven activity against RNA viruses causing lethal hemorrhagic fever (Nipah and Ebola). It is an RNA-dependent RNA polymerase inhibitor capable of inhibiting multiple CoVs . In a mouse SARS virus experimental model, the administration of remdesivir 1 day after the infection reduced the virus titer in the lungs. Similar findings were also observed with a rhesus monkey model of MERV-CoV (26, 27). The preclinical efficacy of remdesivir was confirmed in in vitro studies with Vero E6 cell lines .
The probable therapeutic effect of remdesivir in a patient with SARS-CoV–2 was initially reported in a case report wherein remdesivir was used on compassionate grounds. Although virological improvement and clinical cure were observed in the patient, remdesivir was used only on the sixth day of admission, and the continuous viral load testing revealed that a reduction in viral load had begun before the administration of the drug. Hence, the observed clinical effect might be due to immunity and supportive treatment . A larger prospective cohort of patients treated with remdesivir on compassionate grounds were recently reported by Grein et al. . Of the 61 patients who received at least 1 dose of remdesivir, 53 patients were available for follow-up. After a median follow-up of 18 days, 36 patients (68%) had an improvement in oxygen-support class, including 17 of 30 patients (57%) receiving mechanical ventilation. A total of 25 patients (47%) were discharged, and 7 patients (13%) died with a mortality was 18% (6 of 34) among patients receiving invasive ventilation and 5% (1 of 19) among those not receiving invasive ventilation .
The efficacy of remdesivir was recently evaluated in an RCT involving Chinese patients in comparison with placebo. The study enrolled 237 patients (158 to remdesivir and 79 to placebo) and evaluated the clinical improvement up to day 28. The results of the study revealed a lack of significant difference in time to clinical improvement in patients treated with remdesivir in comparison with placebo (hazard ratio, 1.23 [95% CI, 0.87 to 1.75]). In patients with symptoms for ≤10 days, remdesivir showed better efficacy, (HR, 1.52 [95% CI, 0.95 to 2.43]), albeit without statistical significance .
The early clinical evidence for the efficacy of remdesivir is inconclusive with only marginal efficacy. But owing to the differences in the end points considered in the studies, the precise role of remdesivir may require larger studies with the assessment of both virological and clinical outcomes. At present, there are 22 trials registered in clinicaltrials.gov and 13 studies registered in the WHO-ICTRP.
Corticosteroids are immune modulators that suppress the inflammatory response, thereby minimizing tissue damage. The early observational evidence for the effective use of corticosteroids stems from the lower prevalence of SARS-CoV–2 infection in patients with chronic respiratory disease, suggesting a role for the drugs given for chronic respiratory disease in reducing the prevalence of SARS-CoV–2 infections in such patients . The early preclinical evidence provided by Matsuyama et al. reported effective antiviral activity of ciclesonide in inhibiting the replication of SARS-CoV–2 in epithelial cell lines with an effective concentration of 6.3 µM . Despite the anti-inflammatory effect provided by corticosteroids, they also cause immune suppression, delaying viral clearance .
A recent prospective cohort study conducted by Zha et al. recruited 31 SARS-CoV–2-positive patients treated with corticosteroids (11 patients) or supportive care. The study found no statistically significant association between treatment with corticosteroids and virus clearance time (Hazards ratio (HR), 1.26; 95% CI, 0.58 to 2.74), hospital length of stay (HR, 0.77; 95% CI, 0.33 to 1.78), or duration of symptoms (HR, 0.86; 95% CI, 0.40 to 1.83) . A recent meta-analysis also suggested a higher relative risk for mortality and longer length of stay in patients with SARS-CoV and MERS-CoV treated with corticosteroids .
In a retrospective cohort study conducted by Wang et al., 46 SARS-CoV–2-positive patients treated with either corticosteroids (26) or supportive care (20) were analyzed for clinical outcomes. The mean duration for body temperature back to the normal range was significantly shorter in patients treated with corticosteroids compared with those without the administration of corticosteroids (2.06 ± 0.28 vs. 5.29 ± 0.70; P = 0.010). The patients included in the study had severe pneumonia and were treated early with low dose of corticosteroid, suggesting favorable effect of early, low-dose treatment . On the contrary, another observational study conducted by Lu et al. reported limited effect of adjuvant treatment with corticosteroids in critically ill patients .
The early clinical evidence for the treatment with corticosteroid remains inconclusive. There are 72 RCTs currently under progress to evaluate the efficacy of different corticosteroids at different stages of SARS-CoV–2 infection (clinicaltrials.gov).
Immunotherapy With Convalescent Plasma
The early evidence of the efficacy of convalescent sera was provided by 2 case series from China. In the first study, 5 critically ill patients with acute respiratory distress syndrome (ARDS) were administered convalescent plasma containing neutralizing IgG antibody at a titer of >1:1000 that had been obtained from 5 patients previously recovered from SARS-CoV–2. All the patients were on mechanical ventilation at the time of treatment and previously treated with antiviral agents and methylprednisolone. After the treatment with convalescent sera, body temperature normalized after 3 days in 4 of the 5 patients, and viral loads also became negative after 12 days of treatment. ARDS was resolved in 4 patients after 12 days of treatment, and 3 patients were discharged . In another prospective case series, 10 patients were treated with convalescent sera with a neutralizing antibody titer of >1:640. The radiological examination revealed the resolution of lung lesions after 7 days and virological cure in 7 patients . These findings were also substantiated by a case report of 2 elderly patients treated with convalescent sera from South Korea. Both the patients were previously treated with hydroxychloroquine and lopinavir/ritonavir. Both the patients experienced virological cure after 3 days of treatment with convalescent plasma. The resolution of lung lesions was also observed along with alleviation of other clinical symptoms . Although, the evidence base for immunotherapy with convalescence plasma is supported by only weak quality evidence, it holds promise for future management strategies.
Previous studies on MERV-CoV and SARS-CoV–1 have revealed the release of a plethora of cytokines, including IL–6, which was also confirmed in SARS-CoV–2 infection . Hence, tocilizumab, which is a monoclonal antibody targeting the IL–6, was explored as a treatment option in the treatment of cases with severe SARS-CoV–2 infection. The earliest evidence of its efficacy was provided from a case series by Xu et al. The study included 21 patients (17 severe and 4 critical) who were treated with tocilizumab. Irrespective of the disease severity, all the patients experienced normalization of body temperature 1 day after the treatment with tocilizumab. The oxygen saturation (SpO2) levels were also improved significantly and one-third of patients on ventilator support was put on a noninvasive ventilator a day after the treatment. The percentage of lymphocytes and C-reactive proteins also returned to normal in majority of the patients after 5 days of treatment .
In a subsequent case report, tocilizumab was also used successfully for treating a patient with sickle cell anemia . The patient was hospitalized and, on day 1, developed symptoms of SARS-CoV–2 infection, including fever (38.5°C) and SpO2 dropping to 91% with crackles at pulmonary auscultation. The patient was treated with antibiotics and hydroxychloroquine at a dosage of 200 mg orally every 8 hours while the results of RT-PCR were awaited. The patient was treated with 1 pulse of intravenous tocilizumab at a dosage of 8 mg/kg on day 2 after the deterioration of symptoms and had a positive result in RT-PCR for SARS-CoV–2 infection. The patient experienced clinical cure with an improvement in SpO2 and was discharged on day 5 . Further clinical studies are required to substantiate the utility of tocilizumab in the treatment of SARS-CoV–2 patients.
Other Antiviral Drugs
Among the antiviral drugs, lopinavir, ritonavir, and arbidol were explored in clinical studies involving SARS-CoV-positive patients. In a prospective cohort study conducted by Ye et al., 47 patients treated with either lopinavir/ritonavir or adjuvant treatment were analyzed for efficacy outcomes. The study reported favorable outcomes with respect to lowering body temperature in patients treated with lopinavir/ritonavir in comparison with adjuvant treatment alone .
In a recent RCT, 50 patients with laboratory-confirmed COVID–19 were treated either with lopinavir/ritonavir (34 cases) or arbidol (16 cases). All the patients had mild to moderate SARS-CoV–2 infection without ARDS. The reduction in viral load was the primary end point. After 14 days of treatment, virological cure was observed in all the patients treated with arbidol, but 15 (44.1%) patients treated with lopinavir/ritonavir still had detectable viral load. The study concluded the superior effect of arbidol over lopinavir/ritonavir in the treatment of cases with mild to moderate SARS-CoV infection . In another RCT, 86 patients with mild to moderate SARS-CoV–2 infection were randomly assigned to the lopinavir/ritonavir group (34) or the arbidol group (35) or the no antiviral drug group (17). The primary end point was virological cure. The study reported similar rates and duration of virological cure in all the 3 groups, suggesting lack of clinical efficacy of antiviral drugs in the treatment of cases with mild to moderate SARS-CoV–2 infection .
Preliminary Evidence and Treatment Guidelines
Despite the good-quality early evidence, multiple treatment options were recommended by different nodal agencies. Among the treatment options, hydroxychloroquine, convalescent plasma, and remdesivir are recommended by the Food and Drug Administration (FDA) for the treatment of SARS-CoV infection under specific scenarios . Hydroxychloroquine and chloroquine could be administered only for certain adolescent and adult patients hospitalized with COVID–19, as appropriate. Convalescent plasma and hyperimmune globulin could be used for the treatment based on the availability and accessibility. Remdesivir is provided with an emergency use authorization to treat suspected or laboratory-confirmed COVID–19 in adult and pediatric patients hospitalized with severe disease .
As per the National institute of health (NIH) guidelines, remdesivir was recommended for the treatment of patients hospitalized with severe disease, defined as SpO2 ≤94% on ambient air (at sea level), requiring supplemental oxygen, mechanical ventilation, or extracorporeal membrane oxygenation. The guideline also recommends against high dose of chloroquine (600 mg twice a day) because of cardiac toxicities. The NIH guidelines also recommend against the use of convalescent sera outside the context of RCTs .
Similarly, the Infectious Diseases Society of America (IDSA) guideline also recommends hydroxychloroquine/chloroquine/azithromycin only in the context of clinical trials and not for routine use. Lopinavir/ritonavir and convalescent sera are also recommended only in the context of clinical trials, whereas corticosteroids are recommended only for ARDS in the context of clinical trials. Corticosteroids are not recommended for the treatment of patients with mild to moderate SARS-CoV–2.
A recent Chinese evidence-based guideline recommended the use of α-interferon atomization inhalation (5 million units per time for adults in sterile injection water, twice a day) and lopinavir/ritonavir orally, 2 capsules each time twice a day, based on weak evidences. It also recommended 40 to 80 mg/d methylprednisolone based on weak evidence . On the contrary, Indian National Guidelines for the management of SARS-CoV–2 infection recommends only short-term treatment with glucocorticoids for patients with progressive deterioration of oxygenation indicators (Table 3) . But evidence from real-world studies with Indian healthcare workers have confirmed the prophylactic effect of hydroxychloroquine in health care workers. Hydroxychloroquine is recommended by the Indian council of medical research as a prophylactic drug in high-risk population .
Perspectives on early clinical evidence
The normal workflow in the development of treatment options for any indication involves preclinical to early clinical to late stage clinical trials. But the normal workflow is hampered in case of pandemics. Based on the early evidence available, the therapeutic options available were drugs attenuating either the immunological response (anti-inflammatory drugs) or the viral load (anti-viral agents). Since the pathogenesis of SARS-CoV–2 involves mainly inflammatory responses, the most promising drugs are anti-inflammatory drugs. The inflammatory response is also related to the viral load which makes the selection of ideal endpoint difficult. Considering the fact that the other epidemics of the current century were similar respiratory viruses, a consensus on the most appropriate end point in different categories of patients will also go a long way in mounting faster response with good quality early clinical evidence for future pandemics.
A case in point is the issue with the real-world evidence on the efficacy of hydroxychloroquine. This was a multi-national registry-based study which was one of the earliest evidences in support of hydroxychloroquine for the treatment of SARS-CoV–2. But subsequent clinical trials provided contradictory results that led to the questioning of the results of the study and subsequent journal retraction. In our systematic literature review, this study was also considered as this was an early clinical evidence.
The availability of preprint servers also plays a huge role in dissemination of early stage evidences which is a milieu never faced in the past. Although this leads to faster dissemination, it can also lead to propagation of junk science. We have included evidence from preprint servers also to make a comprehensive appraisal of early stage evidence. Subsequent to the retraction of the Lancet study on hydroxychloroquine, the French study published in the preprint server MedRxiv was also withdrawn. Unlike the journal retractions, preprint retractions do not require substantial explanation on the reasons for retraction. This further complicated the quality of early evidence .
The early-stage evidence available does not convincingly supports in favor of or against a particular therapeutic regimen. This is mainly due to the heterogeneity with respect to the patients, pathogen variants, and the end points. Considering the fact that the last few pandemics were caused by respiratory viruses, drafting a consensus on the most appropriate end point will help in improving the quality of evidences in future pandemics. Furthermore, despite the availability of RCTs, they were of low quality because of the inherent bias (no data on blinding) and imprecision. Considering the fact that the field of evidence medicine is a dynamically evolving field, future studies, especially studies of importance in dealing with medical emergencies, should be appropriately designed to provide reliable and timely evidence. Although the availability of preprint servers facilitates faster dissemination of data, the non-peer-reviewed nature of content needs to be interpreted with caution.