Abstract: International Journal of Infectious Diseases 101 (2020) 283–289 Contents lists available at ScienceDirect International Journal of Infectious Diseases journal homepage: www.elsevier.com/locate/ijid Early hydroxychloroquine but not chloroquine use reduces ICU admission in COVID-19 patients A.J.J. Lammersa,* ,1 , R.M. Brohetb,1 , R.E.P. Theunissena , C. Kostera , R. Roodc, D.W.M. Verhagend , K. Brinkmane , R.J. Hassingf , A. Dofferhoffg , R. el Moussaouih , G. Hermanidesi, J. Ellerbroekj, N. Bokhizzouk , H. Visserl, M. van den Bergem , H. Baxn , D.F. Postmao , P.H.P. Groenevelda a Isala, Zwolle, The Netherlands Department of Epidemiology and Statistics, Isala Academy, Zwolle, The Netherlands c Diakonessen Hospital, Utrecht, The Netherlands d Medisch Centrum Jan van Goyen, Amsterdam, The Netherlands e OLVG, Amsterdam, The Netherlands f Rijnstate, Arnhem, The Netherlands g Canisius Wilhelmina Hospital, Nijmegen, The Netherlands h Maasstad Hospital Rotterdam, The Netherlands i Rode Kruis Hospital, Beverwijk, The Netherlands j Reinier de Graaf Gasthuis, Delft, The Netherlands k BovenIJ Hospital, Amsterdam, The Netherlands l Beatrix Hospital Gorinchem, The Netherlands m Admiraal de Ruiter Hospital, Goes, The Netherlands n Erasmus MC Rotterdam, The Netherlands o University Medical Center Groningen, Groningen, The Netherlands b A R T I C L E I N F O A B S T R A C T Article history: Received 1 August 2020 Received in revised form 23 September 2020 Accepted 23 September 2020 Background: The global push for the use of hydroxychloroquine (HCQ) and chloroquine (CQ) against COVID-19 has resulted in an ongoing discussion about the effectivity and toxicity of these drugs. Recent studies report no effect of (H)CQ on 28-day mortality. We investigated the effect of HCQ and CQ in hospitalized patients on the non-ICU COVID-ward. Methods: A nationwide, observational cohort study was performed in The Netherlands. Hospitals were given the opportunity to decide independently on the use of three different COVID-19 treatment strategies: HCQ, CQ, or no treatment. We compared the outcomes between these groups. The primary outcomes were 1) death on the COVID-19 ward, and 2) transfer to the intensive care unit (ICU). Results: The analysis included 1064 patients from 14 hospitals: 566 patients received treatment with either HCQ (n = 189) or CQ (n = 377), and 498 patients received no treatment. In a multivariate propensitymatched weighted competing regression analysis, there was no significant effect of (H)CQ on mortality on the COVID ward. However, HCQ was associated with a significantly decreased risk of transfer to the ICU (hazard ratio (HR) = 0.47, 95% CI = 0.27–0.82, p = 0.008) when compared with controls. This effect was not found in the CQ group (HR = 0.80, 95% CI = 0.55–1.15, p = 0.207). Conclusion: The results of this observational study demonstrate a lack of effect of (H)CQ on non-ICU mortality. However, we show that the use of HCQ — but not CQ — is associated with a 53% reduction in risk of transfer of COVID-19 patients from the regular ward to the ICU. Recent prospective studies have reported on 28-day, all-cause mortality only; therefore, additional prospective data on the early effects of HCQ in preventing transfer to the ICU are still needed. © 2020 The Author(s). Published by Elsevier Ltd on behalf of International Society for Infectious Diseases. This is an open access article under the CC BY-NC-ND license..