Abstract: SCIENCE CHINA Life Sciences •LETTER TO THE EDITOR• April 2021 Vol.64 No.4: 660–663 https://doi.org/10.1007/s11427-020-1871-4 Evaluation of the efficacy and safety of hydroxychloroquine in comparison with chloroquine in moderate and severe patients with COVID-19 1† 2† 3† 4 5 6 7 Qiuyu Li , Cheng Cui , Fei Xu , Jianping Zhao , Nan Li , Haichao Li , Tianbing Wang , 5 2,8 2 2 2 8 2 Hua Zhang , Na Liu , Yudong Wei , Xiaoye Niu , Yan Xu , Jianping Dong , Xueting Yao , 1 1 2,9 10 10 2* Xiaohong Wang , Yahong Chen , Haiyan Li , Chunli Song , Jie Qiao , Dongyang Liu & 1* Ning Shen 1 Department of Respiratory and Critical Care Medicine, Peking University Third Hospital, Beijing 100191, China; 2 Drug Clinical Trial Center, Peking University Third Hospital, Beijing 100191, China; 3 Department of Respiratory and Critical Care Medicine, the First Affiliated Hospital of Nanchang University, Nanchang 330006, China; 4 Department of Respiratory and Critical Care Medicine, Tongji Hospital, Tongji Medical College, Huazhong University of Science and Technology, Wuhan 430030, China; 5 Research Center of Clinical Epidemiology, Peking University Third Hospital, Beijing 100191, China; 6 Department of Respiratory and Critical Care Medicine, Peking University First Hospital, Beijing 100034, China; 7 Trauma Center, Peking University People’s Hospital, Beijing 100044, China; 8 Beijing Haidian Hospital, Haidian Section of Peking University Third Hospital, Beijing 100080, China; 9 Department of Cardiology, Peking University Third Hospital, Beijing 100191, China; 10 Institute of Medical Innovation, Peking University Third Hospital, Beijing 100191, China Received August 19, 2020; accepted December 18, 2020; published online January 18, 2021 Citation: Li, Q., Cui, C., Xu, F., Zhao, J., Li, N., Li, H., Wang, T., Zhang, H., Liu, N., Wei, Y., et al. (2021). Evaluation of the efficacy and safety of hydroxychloroquine in comparison with chloroquine in moderate and severe patients with COVID-19. Sci China Life Sci 64, 660–663. https://doi.org/ 10.1007/s11427-020-1871-4 Dear Editor, Since December 2019, severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) has been rapidly spreading worldwide. Hydroxychloroquine and chloroquine are candidates for the treatment of coronavirus disease 2019 (COVID-19) owing to its antiviral effect and immunomodulation properties. However, the published results of utilizing hydroxychloroquine and chloroquine as treatment were still controversial and their efficacy and safety in patients with COVID-19 need to be further elucidated. A total of 88 laboratory-confirmed (identified by viral †Contributed equally to this work *Corresponding authors (Ning Shen, email: shenning1972@126.com; Dongyang Liu, email: liudongyang@vip.sina.com) RNA or antibody tests) patients with COVID-19 (65 moderate and 23 severe patients with COVID-19) were included in our multicenter, randomized controlled trial (RCT). Eligible patients randomly assigned in a 1:1 ratio to orally receive hydroxychloroquine (600 mg twice a day on the first day followed by 200 mg twice a day in the last four days) plus standard care or chloroquine (500 mg twice a day for the first three days followed by 250 mg twice a day in the last two days) plus standard care (SC) for 5 days. Our study protocol is provided in the Supplementary Methods. The average age of our patients was 61.3 years old and they had a higher risk of developing severe illness. The average time interval..