Considering that there is still no specific treatment for COVID-19, the identification of effective antiviral agents to foster healing of the disease is urgently needed. An efficient approach would be to testing existing antiviral drugs. Some of these drugs, such as ribavirin, and lopinavir-ritonavir have been used in patients with SARS or MERS, but their effectiveness remains uncertain 20.
Chloroquine has long been used in the treatment of malaria and amoebiasis. However, Plasmodium falciparum has acquired resistance to it and with the emergence of new antimalarials, it is nowadays mostly used for the prophylaxis of the disease. Besides, chloroquine overdose can cause cardiac arrhythmia and death 21. In China, in recent years, chloroquine production has been dramatically reduced due to its low use in clinical practice 22.
Hydroxychloroquine sulfate was synthesized in 1946 by the introduction of a hydroxyl group in chloroquine. In animals, HCQ is less toxic when compared to chloroquine 23. This medication is used to treat systemic autoimmune diseases, such as systemic lupus erythematosus and rheumatoid arthritis. Chloroquine and HCQ have similar chemical structures and mechanisms of action, and because of their anti-viral activity, both could be promising candidates for the treatment of SARS-CoV-2 infection. Hence, several studies have investigated this hypothesis in in vitro experiments.
Wang et al. 11 evaluated the antiviral efficiency of five FDA-approved drugs, including ribavirin, penciclovir, nitazoxanide, nafamostat, chloroquine and two broad- spectrum antiviral drugs, remdesivir and favipiravir. Recently the 2019-nCoV clinical isolate (Vero E6 cells infected with SARS-CoV-2) was used in experiments. Remdesivir and chloroquine were highly effective in reducing viral replication. However, because it is an experimental medication, remdesivir is not available on large scale. Chloroquine showed satisfactory results with an effective concentration (EC) of 6.90 μM, which can be achieved with standard oral doses in humans due to its favorable penetration into tissues, including the lung. The authors demonstrated that chloroquine increases the endosomal pH, interfering within the glycosylation of the SARS-CoV cell receptor and consequently blocking the infection by the virus. The authors also suggest its evaluation in patients affected by the coronavirus, considering the possibility that the immunomodulatory effect of the drug may increase the antiviral effect in vivo.
Yao et al. 15 tested the pharmacological activity of chloroquine and HCQ in Vero E6 cells infected with SARS-Cov-2. Pharmacokinetic models for both drugs were tested separately, mimicking the pulmonary environment, aiming to investigate the most effective regimen according to the drug's safety profile. They concluded that HCQ is more potent than chloroquine to inhibit SARS-CoV-2 in vitro and recommended the oral administration of 400 mg of HCQ twice daily and a maintenance dose of 200 mg twice daily for 4 days.
Liu et al. 22 also evaluated the antiviral effect of HCQ against SARS-CoV-2 infection compared to chloroquine in vitro. The tests were carried out on Vero E6 cells assessing viral activity. The authors found that HCQ inhibited virus penetration into the cell and suggested that clinical trials should be performed.
The in vitro studies mentioned above reported better performance of HCQ when compared to chloroquine for the treatment of SARS-CoV-2. In accordance, the randomized clinical trials conducted by Chen et al. and Gautret et al. 17,18 included in this meta-analysis also found satisfactory results of this drug for the treatment for COVID-19. In contrast, Jun et al. 17 found no benefit in the treatment with HCQ. Of note, none of the three studies analyzed here reported the occurrence of serious adverse effects in patients treated with HCQ.
Like chloroquine, we can affirm that the risk-benefit of using HCQ is favorable to the treatment of COVID-19 since it has satisfactory clinical safety and low risk of interaction with other drugs 9,14. To date, 195 countries have reported cases of the disease, and the low cost of this medication would be of great benefit to health systems, especially for low- and middle-income countries 24.
A consensus of experts recently published by a multi-centric collaborative group from China recommended the use of chloroquine phosphate (500 mg, twice daily and for ten days) for patients diagnosed with mild, moderate and severe SARS-CoV-2 pneumonia, as long as they have no contraindications for the drug use. Other precautions were also recommended, including routine blood exams, electrocardiography and avoiding simultaneous administration of other medications 25.
The Italian Society for Infectious and Tropical Diseases recommended the use of 500 mg of chloroquine twice daily or 200 mg of HCQ for 10 days. However, this treatment period can vary from 5 to 20 days, depending on the intensity of the symptoms presented. This recommendation can be applied for patients who have mild respiratory symptoms and for patients with severe respiratory failure 26.
In our search, we found 43 clinical studies in progress evaluating the use of chloroquine and HCQ to treat COVID-19, registered in the United States of America, China, Brazil and some European countries (Table 2). The world scientific community is committed to the urgent search for effective treatments against COVID-19. Problems to be told, the many trials being performed at the same time will result in a lot of variation regarding the study design, the severity of the symptoms in the included patients, the dosages of medication used and the duration of the treatment. This fact may preclude the comparison of their results, revealing the need to create guidelines for effective trial coordination.
In China, a guideline has been published to coordinate and regulate clinical trials that evaluate treatment alternatives for COVID-19 27. The World Health Organization (WHO) also published a generic protocol for randomized clinical trials that aim to investigate the clinical efficacy and safety of pharmacological treatments for patients with COVID-19 28.
This meta-analysis included the 3 clinical trials available so far. Two of them revealed that the use of HCQ could be efficient in reducing the symptoms presented by patients with COVID-19 and decrease viral detection in the PCR test. Overall, studies have not reported the occurrence of serious side effects during the treatment. In the treatment of lupus, hydroxychloroquine is considered to be a safe medication that has mild side effects. The occurrence of severe adverse effects is rare and is generally related to the cumulative result of the medication or overdose 29. Although these trials were carried out with few patients, it must be taken into account that the performance of clinical studies during the pandemic is hampered by the challenges brought by a new disease, especially concerning its course of development and symptoms presented by the patients.
Genetically, mutations in viral RNA also pose difficulties in establishing therapeutic strategies, such as the development of vaccines. In Brazil, the SARS-Cov-2 genome was sequenced at the Adolfo Lutz Institute and the analyzes indicated that the genome of the first Brazilian patient differs by three mutations from the reference strain in Wuhan, in China. Two of these changes are close to the German strain obtained in Munich, Bavaria 30. It is crutial that the genomic sequencing of the virus in different research centers continues to be performed. This information must be shared with the world scientific community to enhance the understanding of the virus propagation and to assist in the development of new therapies for the emerging strains.
Despite all the efforts that have been made in the search for an effective treatment, the most effective measures for containing the virus are the WHO recommendations, such as social isolation, broad testing and home quarantine 28. In a recent editorial, the Lancet pointed out that countries with a lethargic adoption of these recommendations at the initial phase were more drastically affected by the number of patients and deaths, as is the case of the United Kingdom, the United States and Sweden 31. Brazil is also cited in the editorial, highlighting the weak response of its current president facing the SARS-CoV-2 pandemic. The article emphasizes that countries with fragile health systems should be overburdened soon if the infection is not contained. Despite the existence of few published clinical trials included in our meta-analysis, we believe that the use of HCQ is of paramount importance to prevent patients harboring COVID-19 with moderate symptoms to progress to severe symptoms. Mitigating the intensity of the symptoms would benefit the health systems, reducing the need for intensive care and the use of ventilators.
According to the WHO, there are more than 40 studies of candidate vaccines against COVID-19, all in the development stage and being performed by teams from all over the world. As long as an effective vaccine is not developed, using existing drugs seems very attractive, since the development of a new drug can take years. HCQ is among these drugs, however, more clinical trials are still needed to validate its effectiveness for COVID-19. Designs of available clinical trials that have been included in this meta-analysis have important weaknesses that need to be considered. The studies did not perform tests of excellence as a randomized, multicenter, double-blind clinical trial. In addition, they do not meet the quality standards, especially with regard to patient screening. These deficiencies prevent its results from providing substantial evidence about the efficacy of hydroxychloroquine in the treatment of COVID-19. In spite of the result of this meta-analysis has suggested benefits for the use of hydroxychloroquine, the literature does not have studies that really demonstrate the superiority of this drug in controlling the pandemic. There are ongoing clinical studies, involving a large number of patients, which will provide more consistent evidence about the best treatment to use, which will help to establish individual treatment plans, where side effects are considered and the clinical status of each patient.