COVID-19 (coronavirus disease 2019) has been pandemic around the world by WHO, with millions of people infected currently and causes 5–10% of patients’ deaths. COVID-19 was first reported in December 2019, and the pathogen was firstly isolated on January 7^th, 2020 and then named SARS-CoV-2 by International Committee on Taxonomy of Viruses (ICTV), as it shares great similarity in genomics with the previous emerged SARS-CoV. Chloroquine (CQ) was firstly found to be effective in vitro and then showed promising activity against SARS-CoV-2 infection (2019). Basically, CQ is a classic anti-malarial drug with an immunosuppressive effect as well. Due to the long half-life, it is more prone to be accumulated in vivo and cause various side effects, which may hinder the treatment of COVID-19. Here, we aim to provide rational suggestions to busy clinicians to avoid potential side effects that CQ or its analogs if prescribed to treat COVID-19.

CQ and its analogs were used as anti-malarial agents for decades, and they were derivatives of 4-quinoline, whose origin is quinine. Actually, the anti-malarial agents of quinine were found as early as 1639, and researchers successfully extracted and separated in 1820 (Figure 1). Currently, CQ and hydroxychloroquine (HCQ) were used widely in anti-malarial and in the fields of SLE treatment. The differences between CQ and HCQ were the presence of a hydroxyl group in the side chain in HCQ (Figure 2). Though the lack of large-scale clinical trials, the efficacy and the safety were approximately identical for CQ and HCQ. It is reported that CQ was prone to be more often associated with retinopathy, especially in SLE patients, who were believed to go on a longer course of HCQ treatment (Clotilde et al., 2018). It is noteworthy that CQ and HCQ were reported to have the antiviral activity inagainst SARS [severe acute respiratory syndrome (SARS)] and MERS [Middle East respiratory syndrome (MERS)] in vitro, and clinical research in MERS coronavirus (MERS-CoV) confirmed the efficacy (Al-Bari, 2015; Cortegiani et al., 2020; Hoffmann et al., 2020; Wang et al., 2020). As COVID-19 is pandemic around the world, it is of great importance to explore the promising drugs and nconfirm the efficacy. As SARS-CoV-2 shares a similar structure and target of SARS-CoV, CQ’s antiviral activity has been confirmed quickly in vitro models by Chinese scientists, and multiple clinical trials were still going on. On March 20th 2020, FDA has approved CQ as sympathetic medication for COVID-19 patients (Bulloch, 2020; Coronavirus Task Force, 2020). However, besides their striking activity, CQ and its analogs had many side effects, which should be taken into consideration in clinical practice. The FDA cautions against use of HCQ/CQ for COVID-19 outside of the hospital setting or a clinical trial due to risk of heart rhythm problems (Bulloch, 2020). Here, we summarized the latest developments and pharmacological concerns for CQ and its analogs in order to provide rational consideration for their rational clinical application.

Basically, CQ is the first 4-aminoquinolones reported to be effective in treating coronavirus infection in vitro. The infection of SARS-CoV-2 to target cells is mediated through the interaction of angiotensinconverting enzyme 2 (ACE2) and the viral spike protein (Al-Bari, 2015; Hoffmann et al., 2020). As shown in Figure 3, CQ could elevate the endosomal pH and interfere with terminal glycosylation of ACE2, which thus negatively affect the virus-receptor binding and abrogate the infection. When it comes to SARS-CoV-2, CQ could on the one hand block the interaction between virus “S” protein and host ACE2 protein through influence ACE2 terminal glycosylation and also increase the cytoplasmic PH, which thus inhibit the virus entry and replication (Figure 3) (Al-Bari, 2015; Clotilde et al., 2018; Hoffmann et al., 2020). CQ restriked public hope as the in vitro studies showed its EC50 for SARS-CoV-2 is 1.13 µM, half-cytotoxic concentration CC50 > 100 µM, with the selectivity index of 88.50, the result of which show high SI of CQ when treat COVID-19 and indicate desired safety (Wang et al., 2020). A preliminary clinical trial enrolled over 100 COVID-19 patients proved the efficacy and safety of CQ, and the seventh edition of Chinese Clinical Guidance for COVID-19 recommended the dosage of CQ as follows: 18–65 kg adults with a body weight of >50 kg, 500 mg orally twice daily, continuing for 7 days; body weight of <50 kg patients, taken 500 mg of CQ twice daily for the first 2 days and then followed by 500 mg once daily for the other 5 days (Cortegiani et al., 2020).

The structure of CQ and its analogs was shown in Figure 2. HCQ has the identical structure of CQ, while piperaquine (PQ) possesses the bisquinolines, which is trapped in the acidic digestive vacuole because of their four positive charges (Reuter et al., 2015). Here, we summerized the pharmacology parameters and concerns for these drugs and provide rational consideration for the clinical practitioners.

In fact, the activity of CQ against coronavirus has been noticed as early as 2004, as CQ has been proved to be effective to SARS-CoV in vitro, whose disappearance resulted in limited further research. In vitro research confirmed the efficacy of CQ against SARS-CoV-2 as well as remdesivir. The two compounds remdesivir (EC50, 0.77 µM; CC50 > 100 µM; SI > 129.87) and chloroquine (EC50, 1.13 µM; CC50 > 100 µM; SI > 88.50) potently blocked virus infection at low-micromolar concentration and showed high SI (Wang et al., 2020). Shortly afterward, Chinese researchers confirmed the antiviral activity of HCQ against SARS-CoV-2 and established [physiologically based pharmacokinetic (PBPK) models] PBPK models to optimize the dosage regimen. Xueting Yao et al. found HCQ (EC50 = 0.72 µM) was more potent than chloroquine (EC50 = 5.47 µM) in vitro and simulated PBPK model based on the above in vitro studies (Yao et al., 2020). According to their results, a loading dose of 400 mg twice daily of HCQ orally, followed by a maintenance dose of 200 mg twice daily for 4 days was recommended for COVID-19 patients, as it reached three times the potency of CQ 500 mg twice daily. Till now, there have been 14 clinical trials registered and approved in China to further investigate and compare the efficacy and safety of CQ or HCQ against COVID-19 (Al-Bari, 2015; Yao et al., 2020) (Table 1).

We made database search and analyzed clinical study of HCQ treatment in COVID-19 worldwide and made a meta-analysis up to 4^th May, 2020. Supplementary Figure 1 showed our study selection process. Finally, six papers included in our meta-analysis study. Characteristics of HCQ studies included in our meta-analysis were presented in Table 2 (Chen et al., 2020a; Chen et al., 2020b; Tang et al., 2020; Gautret et al., 2020; Magagnoli et al., 2020; Yu et al., 2020). Meta-analysis was done by RevMan 5, and ramdom effect model was applied. As shown in Figure 4, CT scan indicated pulmonary improvement in 34/45 HCQ group, while there reported only 25/46 improvements in control group (P = 0.04). Additionally, there showed no significant differences in virology conversion rates when COVID-19 patients administered HCQ (P = 0.62) (Figure 5). Nevertheless, HCQ group had a higher risk ratio in inducing adverse reaction, which may due to the pharmacokinetic characteristics of HCQ (P = 0.002) (Figure 6). When it comes to mortality, the results of the two included study seemed to be opposite (Figure 7). Bo Yu et al. suggest that 400 mg of HCQ administered orally daily for 7–10 days could decrease the mortality, especially in critically ill patients, while the research work done by Joseph et al. did not tell the detailed regimen in experimental group. Since there was large heterogeneity in present clinical research, especially in virology conversion comparison and mortality, further high-quality, large-scale clinical study should be made to investigate the efficacy and safety in different subgroups. Above all, HCQ treatment could help alleviate pulmonary disease caused by COVID-19, and its higher incidence of ADRs should be warned in clinical applications. Wuhan Virology Institute warned the lethal dose of CQ was 3–5 g and 1g for adults and pediatrics, respectively (Bruno et al., 1988), and other side effects, such as liver and cardiac toxicity, is not uncommon among COVID-19 infected patients treated with CQ.

Basically, the approved uses of CQ is prophylaxis and treatment of malaria, non-intestinal amebic infection and sarcoidosis (Centers for Disease Control and Prevention (CDC), 2013; Product Information, 2017). 1000-mg initial dose was recommended and followed by 500 mg orally at 6, 24, and 48 h, the entire course of malaria treatment last no more than 2 days. For malaria prophylaxis, 500 mg orally once weekly was recommended 2 weeks prior to travel to the malarious area and continue for 4–8 weeks after leaving (Wang et al., 2020). When it comes to non-intestinal amebic infection and sarcoidosis, the dosage regimen and duration increased up to 3 weeks to 6 months, with maximum daily dosage of 500 mg. In the treatment of COVID-19, it is recommended to take 500 mg twice daily, continuing for 7 days for those weight above 50 kg for adults (18–65 years old) and for those weight below 50 kg for adults, it is recommended to take 500 mg twice daily for the first and second day and 500mg once daily for the next 5 days (2020).

HCQ has raised attention as it shares the identical parent structure of CQ and, most importantly, was reported to be less toxic. In the previous SARS outbreak, HCQ was reported to have anti-SARS-CoV activity in vitro as well (Coronavirus Task Force, 2020). The latest in vitro studies showed that HCQ is more potent for the treatment of COVID-19 than CQ (EC50 = 1.13 µM) as the EC50 of HCQ is 0.72 µM. PBPK modeling revealed that labeled dosage regimen (a loading dose of 400 mg twice daily of HCQ sulfate given orally, followed by a maintenance dose of 200 mg given twice daily for 4 days) could reach three times the potency of CQ phosphate when an HCQ sulfate of 500 mg is twice daily for 5 days in advance (Yao et al., 2020).

Though there is not a yet direct evidence for dihydroartemisinin-PQ (DHA/PQ) in antiviral therapy, we could predict it would have an identical activity as CQ, since PQ is the most active representative of bisquinolines, which used to overcome CQ resistance in malaria therapy (Kaur et al., 2010). Due to the four positive charges, PQ, which shares the bisquinolines structure, may be more efficiently trapped in the acidic digestive vacuole and thus inhibit coronavirus entry and replication (2020). Both population pharmacokinetic modeling and clinical practice demonstrate that DHA/PQ has better cardiac safety than CQ (Chotsiri et al., 2017; Vanachayangkul et al., 2017). Dihydroartemisinin also showed potent anti-virus activity (Gong et al., 2018). The dosage recommended for falciparum malaria treatment is based on weight, basically, 960 mg of PQ/120 mg of DHA orally once daily for 3 days for 36–75 kg adults (Product Information, 2012). Above all, DHA/PQ may serve as a rationale candidate in COVID-19 treatment.

Orally taking CQ is rapidly and almost completely absorbed from the gastrointestinal tract (Dattani and Rajput, 2010; Lee et al., 2012). Plasma protein binding of CQ is approximately 55%. After absorption, CQ is extensively distributed in body tissues and fluids. Besides, it could cross the placenta barrier and secrete into breast milk, which may be a risk for pregnancies and breast-feeding babies. It is mainly metabolized in the liver by CYP2C8, CYP3A4, and CYP2D6 with the metabolized product retained activity (Ducharme and Farinotti, 1996). The elimination half-life is as long as 108–291 h, with ~55% eliminated through the kidneys (Ducharme and Farinotti, 1996; Dattani and Rajput, 2010; Lee et al., 2012; Product Information, 2012). As HCQ has an identical structure of CQ, it possessed the same PK characteristics (high accumulation in cells and prolonged elimination half-life). Thus, a high loading dose and low maintenance dose was recommended to avoid adverse effects (Yao et al., 2020).

Additionally, there was also a clinical trial registered in China considering the application of DHA/PQ against COVID-19, though canceled due to lack of patients in the end (ChiCTR2000030082). Identical with CQ, DHA/PQ is mainly absorbed after taken orally, with peak plasma concentrations reached within 3–6 h for PQ and 1–3 h for DHA. PQ is then extensively distributed throughout the body, with a higher protein binding activity (more than 99% bound to plasma proteins). Besides, DHA has a smaller volume of distribution and plasma protein binding of 44–93%. The half-life of PQ was reported to be around (13.5–28days), while the elimination of DHA is much more rapid (with a half-life of ~1 h) (Kim et al., 2003; Hoglund et al., 2012).

Additionally, high-fat and high-calorie food intake could significantly increase the AUC and bioavailability of this drug, especially PQ, which may increase the risks of side effects. Consequently, it is recommended that DHA/PQ not be administered within ± 3 h of food consumption, especially for patients consuming a typical Western diet or taken with a low fat content of standard meals when co-administered with DHA/PQ (Tarning et al., 2008). The pharmacokinetic parameters of CQ and its analogs were shown in Table 3.

With the development of genomics, the association of pharmacogenomics and anti-malarial drug metabolism have analyzed in recent years. CQ mainly metabolized by CYP3A4/CYP3A5 and CYP2C8 and CYP2D6, while only CYP2C8 SNPs were reported to influence clinical outcomes (Reuter, 2015). Additionally, CYP2D6 SNPs could influence the blood levels of HCQ (Elewa and Kyle, 2017). In vitro metabolism experiments revealed that CYP3A4 and CYP2C8 were the main metabolize enzyme of PQ, while CYP3A4 had a higher metabolic rate (Lee et al., 2016). Pharmacogenomic SNPs and pharmacokinetics of CQs as shown in Table 4. Additionally, CQ and HCQ were reported to be the substrate and inhibitor human organic anion transporting polypeptide 1A2, which believed to be one of the reasons for the vision impairment, as this effect may compromise the function of the classic visual cycle (Yao et al., 2020).

Since COVID-19 is warned by WHO as a pandemic around the world, it is of great importance to explore active drugs. CQ and its several analogs, especially HCQ, showed promising antiviral activity in vitro and preliminary clinical studies confirmed its efficacy. Nevertheless, adverse effects induced by CQ or its analogs should not be ignored due to their long half-lives and are lethal in large accumulated doses. As CQ or its analogs were inhibitors or substrate of CYP450, we suggest clinicians to assess the drug-to-drug interactions before use so as to avoid severe side effects, such as cardiac toxicity, liver damage, ocular toxicity, etc. Though CQ or HCQ had not shown significant advantages in virology conversion, the immuno-regulatory effect may help the body to combat the COVID-19. When it comes to the special population, such as the elderly, pregnant women, it should be carefully weighed the potential benefits of drug treatment against potential risks before prescribing. The metabolism of the elderly and the pediatric patients varied from the adults, which should be taken into full consideration. Additionally, patients with cardiac disease should be ruled out and monitored the side effects more carefully.

Recently, the US FDA has revoked the emergency use authorization (EUA) that allowed for CQ and HCQ to treat certain hospitalized patients with COVID-19 due to the emerging scientific data. The US FDA announced that “In light of ongoing serious cardiac adverse events and other potential serious side effects, the known and potential benefits of CQ/HCQ no longer outweigh the known and potential risks for the authorised use;” however, the efficacy and safety of CQ/HCQ in COVID-19 is controversial. The Lancet journal has retracted a large study of HCQ after finding flaws in the dataset, which published on 22 May. The study found the drug did not help treat COVID-19. Chinese scientists Nanshan et al. reported their study compared the efficacy of CQ in COVID-19 treatment (Huang et al., 2020). They enrolled 197 patients completed CQ treatment, and 176 patients were included as historical controls. The median time to achieve an undetectable viral RNA was 6-day shorter in chloroquine than in non-chloroquine. No serious adverse events were observed in the chloroquine group.

Above all, high-quality, large-scale clinical research still need to be done to assess the potential benefits and risks for different patients, and PBPK modeling may help optimize the clinical dosing design. It is of great importance for all the clinical participants or coordinates together to overcome the COVID-19 crisis.

HP, ZC, SR, JW, MZ, CZ, LD, YZ, and LC prepared the manuscript and do the literature research. HP, ZC, TX, and XL wrote the manuscript. JH, XW, and TH did the article review and the corresponding author TH and XW approved the final version. All authors contributed to the article and approved the submitted version.

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.