Limitations
We reviewed the information provided by all clinical trials focused on HQ and chloroquine for patients diagnosed with COVID-19 available in the WHO-ICTRP database until April 8th, 2020, at 10:30 GMT-6. We chose the WHO-ICTRP because it compiles data from ClinicalTrials.gov and 10 primary registers (https://www.who.int/ictrp/en/). In the scenario of the COVID-19 pandemic, we judged that this approach would provide an improved overview of clinical trials being planned in different countries. Nevertheless, as we did not search the primary registers directly, it is possible that some potentially eligible registered RCTs could have been missed. Also, the data analyzed in this study is limited to the information provided in the record of the clinical trials’ register. A minority of the clinical trials provided access to the full study protocol; therefore, the data collected and analyzed in this study may be incomplete if authors have deliberately left information missing on the publicly available record of the planned trials. Nevertheless, if the trial registers are incomplete for low quality designs or deliberate actions, this represents a risk to the strength of the evidence that will ultimately be available to inform decisions. Finally, as the development of research on COVID-19 is evolving fast, additional RCTs may exist which were planned but registered after the study timeline; these trials were not included in the present analysis.