Abstract: The n e w e ng l a n d j o u r na l of m e dic i n e Original Article Observational Study of Hydroxychloroquine in Hospitalized Patients with Covid-19 Joshua Geleris, M.D., Yifei Sun, Ph.D., Jonathan Platt, Ph.D., Jason Zucker, M.D., Matthew Baldwin, M.D., George Hripcsak, M.D., Angelena Labella, M.D., Daniel K. Manson, M.D., Christine Kubin, Pharm.D., R. Graham Barr, M.D., Dr.P.H., Magdalena E. Sobieszczyk, M.D., M.P.H., and Neil W. Schluger, M.D.​​ A BS T R AC T BACKGROUND Hydroxychloroquine has been widely administered to patients with Covid-19 without robust evidence supporting its use. METHODS We examined the association between hydroxychloroquine use and intubation or death at a large medical center in New York City. Data were obtained regarding consecutive patients hospitalized with Covid-19, excluding those who were intubated, died, or discharged within 24 hours after presentation to the emergency department (study baseline). The primary end point was a composite of intubation or death in a time-to-event analysis. We compared outcomes in patients who received hydroxychloroquine with those in patients who did not, using a multivariable Cox model with inverse probability weighting according to the propensity score. RESULTS Of 1446 consecutive patients, 70 patients were intubated, died, or discharged within 24 hours after presentation and were excluded from the analysis. Of the remaining 1376 patients, during a median follow-up of 22.5 days, 811 (58.9%) received hydroxychloroquine (600 mg twice on day 1, then 400 mg daily for a median of 5 days); 45.8% of the patients were treated within 24 hours after presentation to the emergency department, and 85.9% within 48 hours. Hydroxychloroquine-treated patients were more severely ill at baseline than those who did not receive hydroxychloroquine (median ratio of partial pressure of arterial oxygen to the fraction of inspired oxygen, 223 vs. 360). Overall, 346 patients (25.1%) had a primary end-point event (180 patients were intubated, of whom 66 subsequently died, and 166 died without intubation). In the main analysis, there was no significant association between hydroxychloroquine use and intubation or death (hazard ratio, 1.04, 95% confidence interval, 0.82 to 1.32). Results were similar in multiple sensitivity analyses. From the Divisions of General Medicine, Infectious Diseases, and Pulmonary, Allergy, and Critical Care Medicine, Department of Medicine (J.G., J.Z., M.B., A.L., D.K.M., C.K., R.G.B., M.E.S., N.W.S.), the Departments of Biostatistics (Y.S.) and Epidemiology (J.P., R.G.B., N.W.S.), Mailman School of Public Health, and the Department of Biomedical Informatics (G.H.), Vagelos College of Physicians and Surgeons, Columbia University, and New York–Presbyterian Hospital–Columbia University Irving Medical Center (J.G., J.Z., M.B., A.L., D.K.M., C.K.,R.G.B., M.E.S., N.W.S.) — all in New York. Address reprint requests to Dr. Schluger at the Division of Pulmonary, Allergy, and Critical Care Medicine, Columbia University Irving Medical Center, PH-8 E., Rm. 101, 622 W. 168th St., New York, NY 10032, or at ­ns311@​­cumc​.­columbia​.­edu. This article was published on May 7, 2020, and updated on May 14, 2020, at NEJM.org. N Engl J Med 2020;382:2411-8. DOI: 10.1056/NEJMoa2012410 Copyright © 2020 Massachusetts Medical Society. CONCLUSIONS In this observational study involving patients with Covid-19 who had been admitted to the hospital, hydroxychloroquine administration was..