Background COVID-19 is pandemic with high mortality among hospitalized patients despite a benign course in the large majority of patients infected. Limited data are available from small outpatient studies and have not shown efficacy in preventing hospitalization. Hydroxychloroquine (HCQ) and chloroquine have antiviral and immune-modulating effects, but there are no data concerning their efficacy in reducing viral load and shedding in outpatients.

Evidence supporting possible efficacy for hydroxychloroquine. In cell models, chloroquine both interferes with terminal glycosylation of the ACE2 receptor (the cell surface receptor by which SARS-CoV2 enters human cells) and increases endosomal pH, which interferes (at least in vitro) with a crucial step in viral replication.1,2 HCQ is 5x more potent than chloroquine in a Vero cell model of SARS-CoV-2 infection. In independent experiments, chloroquine has confirmed in vitro activity against SARS-CoV-2. Additionally, HCQ has in vitro efficacy against SARS-CoV-1. According to news releases, an as-yet-unpublished set of case series in China (N reportedly 120) suggests the possibility of rapid viral clearance and low rates of progression to critical illness. In addition to in vitro anti-viral effects chloroquine and HCQ appear to have immune-modulatory effects, especially via suppression of release of TNF and IL6, especially in macrophages.

Evidence against efficacy for hydroxychloroquine. Chloroquine and HCQ have been promoted as extremely broad anti-infective agents for decades. The reported effects include suppression of fungi, atypical bacteria, and viruses. Other than the effects on ACE2 glycosylation, the mechanisms invoked as evidence for efficacy against SARS-CoV-2 have also been invoked for a wide range of viruses. However, when chloroquine and HCQ have been studied in humans, neither agent has demonstrated consistent efficacy in clinical trials, including in HIV, influenza, hepatitis, and Dengue. In one trial, chloroquine resulted in increased viral replication in Chikungunya virus \[Roques et al, Viruses 2018 May 17;10(5)\] while in another hydroxychloroquine was associated with increased HIV viral load \[Paton et al, JAMA 2012 Jul 25;308(4):353\]. Expert opinion advises against HCQ for MERS, another serious coronavirus. An underpowered (n=30) study of HCQ in COVID-19 recently published in China did not demonstrate any clinical benefit \[Chen et al, J Zhejiang University, 2020 March 9\]. The long history of clinical failure despite in vitro anti-viral activity suggests a low probability of efficacy.

Rationale for Trial There is significant publicity concerning the potential use of HCQ in this pandemic, and many patients are seeking access to this unproven therapy. The ANZICS guidelines emphasize that novel treatments should be administered within clinical trials; the Surviving Sepsis Campaign guidelines (http://bit.ly/SSCCOVID-19) also affirm the lack of evidence to support the clinical use of (hydroxy)chloroquine. WHO guidance (https://apps.who.int/iris/bitstream/handle/10665/331446/WHO-2019-nCoV-clinical-2020.4-eng.pdf) also strongly affirms that "investigational anti-COVID-19 therapeutics should be done under ethically approved, randomized, controlled trials." The evidence thus strongly favors equipoise.