Abstract: Original Investigation | Infectious Diseases Effect of High vs Low Doses of Chloroquine Diphosphate as Adjunctive Therapy for Patients Hospitalized With Severe Acute Respiratory Syndrome Coronavirus 2 (SARS-CoV-2) Infection A Randomized Clinical Trial Mayla Gabriela Silva Borba, MD; Fernando Fonseca Almeida Val, PhD; Vanderson Souza Sampaio, PhD; Marcia Almeida Araújo Alexandre, MD; Gisely Cardoso Melo, PhD; Marcelo Brito, MSc; Maria Paula Gomes Mourão, MD; José Diego Brito-Sousa, MSc; Djane Baía-da-Silva, PhD; Marcus Vinitius Farias Guerra, MD; Ludhmila Abrahão Hajjar, MD; Rosemary Costa Pinto, BSc; Antonio Alcirley Silva Balieiro, MSc; Antônio Guilherme Fonseca Pacheco, MD; James Dean Oliveira Santos Jr, PhD; Felipe Gomes Naveca, PhD; Mariana Simão Xavier, MSc; André Machado Siqueira, MD; Alexandre Schwarzbold, MD; Júlio Croda, MD; Maurício Lacerda Nogueira, MD; Gustavo Adolfo Sierra Romero, MD; Quique Bassat, MD; Cor Jesus Fontes, MD; Bernardino Cláudio Albuquerque, MD; Cláudio-Tadeu Daniel-Ribeiro, MD; Wuelton Marcelo Monteiro, PhD; Marcus Vinícius Guimarães Lacerda, MD; for the CloroCovid-19 Team Abstract Key Points IMPORTANCE There is no specific antiviral therapy recommended for coronavirus disease 2019 (COVID-19). In vitro studies indicate that the antiviral effect of chloroquine diphosphate (CQ) requires a high concentration of the drug. Question How safe and effective are 2 different regimens of chloroquine diphosphate in the treatment of severe coronavirus disease 2019 (COVID-19)? OBJECTIVE To evaluate the safety and efficacy of 2 CQ dosages in patients with severe COVID-19. Findings In this phase IIb randomized clinical trial of 81 patients with COVID-19, DESIGN, SETTING, AND PARTICIPANTS This parallel, double-masked, randomized, phase IIb an unplanned interim analysis clinical trial with 81 adult patients who were hospitalized with severe acute respiratory syndrome recommended by an independent data coronavirus 2 (SARS-CoV-2) infection was conducted from March 23 to April 5, 2020, at a tertiary safety and monitoring board found that care facility in Manaus, Brazilian Amazon. a higher dosage of chloroquine diphosphate for 10 days was associated INTERVENTIONS Patients were allocated to receive high-dosage CQ (ie, 600 mg CQ twice daily for with more toxic effects and lethality, 10 days) or low-dosage CQ (ie, 450 mg twice daily on day 1 and once daily for 4 days). particularly affecting QTc interval prolongation. The limited sample size MAIN OUTCOMES AND MEASURES Primary outcome was reduction in lethality by at least 50% in did not allow the study to show any the high-dosage group compared with the low-dosage group. Data presented here refer primarily benefit overall regarding treatment to safety and lethality outcomes during treatment on day 13. Secondary end points included efficacy. participant clinical status, laboratory examinations, and electrocardiogram results. Outcomes will be presented to day 28. Viral respiratory secretion RNA detection was performed on days 0 and 4. Meaning The preliminary findings from the CloroCovid-19 trial suggest that higher dosage of chloroquine should not RESULTS Out of a predefined sample size of 440 patients, 81 were enrolled (41 [50.6%] to highdosage group and 40 [49.4%] to low-dosage group). Enrolled patients had a mean (SD) age of 51.1 (13.9) years, and most (60 [75.3%]) were men. Older age (mean [SD] age, 54.7 [13.7] years vs 47.4 [13.3] years) and more heart..