Abstract: Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 9 May 2020 doi:10.20944/preprints202005.0057.v2 Early hydroxychloroquine is associated with an increase of survival in COVID-19 patients: an observational study. Membrillo FJ1,2**, Ramírez-Olivencia G*1,7, Estébanez M*1,7, de Dios B*1,7, Herrero MD*1,7, Mata T*1,7, Borobia AM3, Gutierrez C4, Simón M5, Ochoa A6, Martinez Y1, Aguirre A8 , Alcántara F9, Fernández P9, López E8, Valle P3, Campos S6, Navarro M7, Ballester E1, on behalf of the COVID19 Central Defense Hospital “Gómez Ulla” Team (annex 1) 1: CRBN & Infectious Diseases Unit. HLIU. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. 2: Infectious Diseases Unit. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. 3: Clinical Pharmacology Department. La Paz Hospital, Madrid, Spain. 4: Preventive Medicine Department. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. 5: Microbiology Department. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. 6: Pneumology Department. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. 7: Internal Medicine Department. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. 8: Ophthalmology Department. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. 9: Dermatology Department. Central Defense Hospital “Gómez Ulla”, Madrid, Spain. *contributed equally **corresponding author. Francisco Javier Membrillo de Novales. CRBN & Infectious Diseases Unit. Central Defense Hospital “Gómez Ulla”. Glorieta del Ejército, s/n, 28047 Madrid (Spain). fmemnov@oc.mde.es © 2020 by the author(s). Distributed under a Creative Commons CC BY license. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 9 May 2020 doi:10.20944/preprints202005.0057.v2 Summary: Hydroxychloroquine has shown in vitro activity against SARS-CoV-2. Here we present an observational study. We analysed data from 164 patients admitted to our hospital diagnosed with COVID-19. Hydroxychloroquine treatment was associated with an increase in the mean cumulative survival. Preprints (www.preprints.org) | NOT PEER-REVIEWED | Posted: 9 May 2020 doi:10.20944/preprints202005.0057.v2 ABSTRACT Background: Although no specific treatment for COVID 19 has been proven effective yet, some drugs with in vitro potential against SARS-CoV-2 virus have been proposed for clinical use. Hydroxychloroquine has in vitro anti-viral and immunomodulatory activity, but there is no current clinical evidence of its effectiveness on the outcome of the disease. Methods: We enrolled all 18-85 years old inpatients from Central Defense Hospital, Madrid, Spain, who were hospitalised due to COVID-19 and had a definitive outcome (either dead or discharged). We used a statistical survival analysis. Results: We analysed 220 medical records. 166 patients met the inclusion criteria. 48,8 % of patients not treated with HCQ died, versus 22% in the group of hydroxychloroquine (p=0,002). According to clinical picture at admission, hydroxychloroquine increased the mean cumulative survival in all groups from 1,4 to 1,8 times. This difference was statistically significant in the mild group. Conclusions: in a cohort of 166 patients between 18 to 85 years hospitalised with COVID-19, hydroxychloroquine treatment with an initial loading dose of 800mg improved patient survival when admitted in early stages of the disease. There was a non-statistically significant trend towards survival in all groups, which will need to be clarified in subsequent studies. Type of..