Abstract: BioScience Trends. 2020; 14(2):156-158. Communication 156 DOI: 10.5582/bst.2020.03072 Update on use of chloroquine/hydroxychloroquine to treat coronavirus disease 2019 (COVID-19) Jianjun Gao1,*, Shasha Hu2 1 2 Department of Pharmacology, School of Pharmacy, Qingdao University, Qingdao, China; Department of Pathology, the Affiliated Hospital of Qingdao University, Qingdao, China. SUMMARY Drugs that are specifically efficacious against SARS-CoV-2 have yet to be established. Chloroquine and hydroxychloroquine have garnered considerable attention for their potential to treat coronavirus disease 2019 (COVID-19). Increasing evidence obtained from completed clinical studies indicates the prospects for chloroquine/hydroxychloroquine to treat COVID-19. More randomized control clinical studies are warranted to determine the feasibility of these two drugs in treating COVID-19. Keywords SARS-CoV-2, COVID-19, chloroquine, hydroxychloroquine Coronavirus disease 2019 (COVID-19) has caused more than 1 million confirmed cases and approximately 70,000 deaths worldwide as of April 6, 2020 (1). Drugs that are specifically efficacious against SARS-CoV-2 have yet to be established. Chloroquine and hydroxychloroquine have garnered considerable attention for their potential to treat COVID-19. In China, chloroquine was added to the "Guidance for Corona Virus Disease 2019: Prevention, Control, Diagnosis, and Management" issued by the National Health Commission on February 18, 2020 (2). The U.S. Food and Drug Administration (FDA) issued an emergency use authorization for chloroquine/ hydroxychloroquine to treat COVID-19 on March 28, 2020 (3). The European Medicines Agency contended that the two drugs should be used in clinical trials or national emergency use programs for the treatment of COVID-19 on April 1, 2020 (4). The low cost and easy availability of chloroquine/hydroxychloroquine may help to curb this global public health emergency if their efficacy and safety are ultimately verified in clinical studies. Chloroquine phosphate is the first drug reported to display efficacy against COVID-19 in early clinical studies in China (5,6). Based on this encouraging finding, chloroquine phosphate was added to the Sixth Edition of the Guidance for tentative treatment of COVID-19 (2). The Sixth Edition recommended that adult patients in whom chloroquine is not contraindicated should take chloroquine phosphate tablets, 500 mg (300 mg for chloroquine) twice a day for no more than 10 days (7). To reduce the risk of adverse effects of chloroquine, the Seventh Edition of the Guidance, issued on March 3, 2020, recommends a reduced dosage and shortened duration of treatment (8). Specifically, the dosage of chloroquine phosphate for adult patients (ages 18-65) with a body weight greater than 50 kg is 500 mg twice a day for 7 days and that for adult patients (ages 18-65) with a body weight less than 50 kg is 500 mg twice a day for the first 2 days and 500 mg once a day for the following 3-7 days (8). Regarding the treatment strategy, chloroquine and another antiviral favipiravir that also displayed efficacy in clinical trials are highlighted for their use in mild and moderate COVID-19 cases to prevent disease progression (9). In a pilot study (10) aiming to evaluate the efficacy and safety of chloroquine in inpatients with COVID-19, 10 patients (3 with severe disease and 7 with moderate disease) received chloroquine phosphate 500 mg orally twice a day for 10 days, and..