Bias as a source of inconsistency in ivermectin trials for COVID-19: A systematic review

Background and purpose The objective of this systematic review is to summarize the effects of ivermectin for the prevention and treatment of patients with COVID-19 and to assess inconsistencies in results from individual studies with focus on risk of bias due to methodological limitations. Evidence review We searched the L.OVE platform through July 6, 2021 and included randomized trials (RCTs) comparing ivermectin to standard or other active treatments. We conducted random-effects pairwise meta-analysis, assessed the certainty of evidence using the GRADE approach and performed sensitivity analysis excluding trials with risk of bias. Results We included 29 RCTs which enrolled 5592 cases. Overall, the certainty of the evidence was very low to low. Compared to standard of care, ivermectin may reduce mortality, may increase symptom resolution or improvement, may increase viral clearance, may reduce infections in exposed individuals and may decrease hospitalizations (Risk difference (RD) 21 fewer per 1000, 95%CI: 35 fewer to 4 more). However, after excluding trials classified as “high risk” or “some concerns” in the risk of bias assessment, most estimates of effect changed substantially: Compared to standard of care, low certainty evidence suggests that ivermectin may not significantly reduce mortality (RD 7 fewer per 1000, 95%CI: 77 fewer to 108 more) nor mechanical ventilation (RD 6 more per 1000, 95%CI: 43 fewer to 86 more), and moderate certainty evidence shows that it probably does not significantly increase symptom resolution or improvement (RD 14 more per 1000, 95%CI: 29 fewer to 71 more) nor viral clearance (RD 12 fewer per 1000, 95%CI: 84 fewer to 76 more). It is uncertain if ivermectin increases or decreases severe adverse events and symptomatic infections in exposed individuals. Conclusions and Relevance Ivermectin may not improve clinically important outcomes in patients with COVID-19 and its effects as a prophylactic intervention in exposed individuals are uncertain. Previous reports concluding significant benefits associated with ivermectin are based on potentially biased results reported by studies with substantial methodological limitations. Further research is needed. ### Competing Interest Statement The authors have declared no competing interest. ### Funding Statement None ### Author Declarations I confirm all relevant ethical guidelines have been followed, and any necessary IRB and/or ethics committee approvals have been obtained. Yes The details of the IRB/oversight body that provided approval or exemption for the research described are given below: The study is a systematic review for which public information was used. All necessary patient/participant consent has been obtained and the appropriate institutional forms have been archived. Yes I understand that all clinical trials and any other prospective interventional studies must be registered with an ICMJE-approved registry, such as ClinicalTrials.gov. I confirm that any such study reported in the manuscript has been registered and the trial registration ID is provided (note: if posting a prospective study registered retrospectively, please provide a statement in the trial ID field explaining why the study was not registered in advance). Yes I have followed all appropriate research reporting guidelines and uploaded the relevant EQUATOR Network research reporting checklist(s) and other pertinent material as supplementary files, if applicable. Yes All data is available in the main manuscript and/or supplementary materials