The systematic review of the literature was conducted in line with PRISMA guidelines and Cochrane handbook [9,10], and was registered at Prospero database (CRD42020197070) [11]. It included all randomized controlled trials (RCTs) published, which assessed COVID-19 patients aged 18 years or older, who were treated with chloroquine or hydroxychloroquine, at any dose, and compared to a control group that received other experimental antiviral treatment, supportive treatment or placebo. We excluded prevention or post-exposure prophylaxis studies.
Search strategy
We searched the Cochrane Central Register of Controlled Trials (CENTRAL; in The Cochrane Library current issue), MEDLINE, EMBASE, and LILACS (2019 to March 2021). We also searched the WHO Clinical Trials Registry for ongoing and recently completed studies, and the reference lists of selected articles and reviews for possible relevant studies, with no restrictions regarding language or publication status.
In MEDLINE (PubMed), we combined the subject-specific search ((("coronavirus"[mesh terms]) or (coronavirus*[title/abstract] or coronovirus*[title/abstract] or coronavirinae*[title/abstract] or coronavirus*[title/abstract] or coronovirus*[title/abstract] or wuhan*[title/abstract] or hubei*[title/abstract] or huaian[title/abstract] or "2019-ncov"[title/abstract] or 2019ncov[title/abstract] or ncov2019[title/abstract] or "ncov-2019"[title/abstract] or "covid-19"[title/abstract] or covid19[title/abstract] or "hcov-19"[title/abstract] or hcov19[title/abstract] or cov[title/abstract] or "2019 novel*"[title/abstract] or ncov[title/abstract] or "n-cov"[title/abstract] or "sars-cov-2"[title/abstract] or "sarscov-2"[title/abstract] or "sarscov2"[title/abstract] or "sars-cov2"[title/abstract] or "sars-cov-19"[title/abstract] or ncorona*[title/abstract])) AND (((((((Hydroxychloroquine[MeSH Terms]) OR (Chloroquine[MeSH Terms])) OR (chloroquin*[Title/Abstract])) OR (Hydroxychloroquin*[Title/Abstract])) OR (Oxychloroquin*[Title/Abstract])) OR (antimalaria*[Title/Abstract])) OR (anti‐malaria*[Title/Abstract]))). Search strategies were adapted to The Cochrane Library (Wiley InterScience), EMBASE (Ovid Web), and LILACS.
Selection of studies
Two authors (ML and VYM) independently identified and selected potentially eligible studies for inclusion in the review. Any disagreements were resolved by discussion and consensus. A third author was included in the discussion, if needed. The review authors were not blinded to the journal or authors.
Data extraction
Two authors (ML and LLM) independently extracted the following data using a specific extraction form: characteristics of the study including study design, duration of the study, if the protocol was published before recruitment of patients, funding sources, and details of trial registration; characteristics of the study including place of study, number of participants assigned, number of participants assessed, inclusion criteria, exclusion criteria and age; characteristics of the study interventions including timing and type of intervention and control, and any co-interventions; characteristics of the study outcomes including the length of follow-up, loss to follow-up, and outcome measures; and the methodological domains looking for risk of bias. Any disagreements were resolved by discussion.
The risk of bias of the included studies was assessed by two independent authors (ML and VYM). As recommended by The Cochrane Collaboration Risk of Bias tool [12], we assessed the following domains: random sequence generation; allocation concealment; blinding of participants and personnel; blinding of outcome assessment; incomplete outcome data; selective reporting; and other bias (e.g., major baseline imbalance). Each of these criteria was evaluated using low risk of bias; high risk of bias; and unclear (either lack of information or uncertainty over potential for bias). Disagreements between authors regarding the risk of bias for the domains were resolved by discussion.
Outcomes
The primary outcome was all-cause mortality. As second outcome, we evaluated serious adverse events of HCQ treatment (life-threatening or requiring hospitalization or adverse events that resulted in discontinuation of treatment). Other outcomes could not be assessed due to substantial heterogeneity between measurements and outcomes of the included studies.
Statistical analysis
We combined the results of the included trials by performing a meta-analysis, using the Review Manager version 5.0 (The Cochrane Collaboration), and a p-value less than 0.05 was considered significant [13]. For rate comparisons, we calculated the risk ratio (RR) with a 95% confidence interval (95%CI) for individual studies. We pooled similar studies using a random-effects model, according to the Mantel and Haenszel method for estimating the RR and its 95%CI, and pooled data are shown in forest plots.
The unit of randomization for all trials included was the individual participant of study. There were no unit of analysis issues when considering cluster-randomized trials. Where appropriate, problems of unit of analysis with multiple reporting of outcomes, such as different follow-up times were solved by presenting these separately.
The presence of heterogeneity among the studies was estimated by the Cochran´s Q statistic and measured by the I2 value, and heterogeneity was considered present for I2>50%. Data from the systematic review were grouped, and the weighted average was calculated as the studies’ summary measure. Funnel plots were obtained to estimate the publication bias.
Assessment of quality of evidence and 'Summary of findings' table
The GRADE approach was used to assess the quality of evidence related to two outcomes – mortality and serious adverse events [14]. Quality of evidence was categorized as ‘high’, ‘moderate’, ‘low’, or ‘very low’, depending on the presence and extent of five factors: risk of bias, inconsistency of effect, indirectness, imprecision, and publication bias.
The main results of the use of hydroxychloroquine to treat participants with COVID-19 are presented in a 'Summary of findings' table, which provides key information concerning quality of evidence, magnitude of effect of the interventions examined, and the sum of available data on the main outcomes.