Continuous use of metformin in patients receiving contrast medium: what is the evidence? A systematic review and meta-analysis

Substantial inconsistencies exist in current guidelines regarding recommendations of metformin usage with the administration of a contrast medium. We aimed to perform a meta-analysis to determine whether the risks of contrast-induced acute kidney injury (CI-AKI) and lactic acidosis increase with metformin use in diabetic patients receiving a contrast medium.Studies were retrieved from databases from inception to May 15, 2021. Studies that compared the outcomes of using metformin with not using metformin during contrast medium administration were included. The primary outcomes were incidence of CI-AKI and lactic acidosis. The secondary outcomes were renal function changes from baseline. Data analysis was using risk ratio (RR) for dichotomous outcomes and mean differences (MD) with 95% confidence intervals (CI) for continuous outcomes.Analyses of two randomized controlled trials and four retrospective cohorts examining a total of 1459 patients revealed no significant differences in the incidence of CI-AKI (RR = 1.08; 95% CI, 0.72 to 1.63) and in changes in renal function measurements (serum creatinine: MD = 0.00 mg/dL, 95% CI, - 0.05 to 0.05; estimated glomerular filtration rate: MD = 0.22, 95% CI, - 2.47 to 2.91) after contrast medium administration between patients using and not using metformin.There is no evidence that continuing metformin during contrast medium administration is associated with a higher risk of CI-AKI, lactic acidosis, or renal function deterioration compared to patients who discontinued metformin or who were not metformin users. The limited quality of the included studies may compromise the strength of evidence provided in this meta-analysis.There is no need to discontinue metformin either before or after intravenous contrast medium exposure in patients with eGFR > 30 mL/min/1.73 m2. In patients receiving intra-arterial contrast medium with first-pass renal exposure, there is no need to withhold metformin if eGFR is above 60 mL/min/1.73 m2. For patients who have an eGFR level between 30 and 60 mL/min/1.73 m2 and are receiving intra-arterial contrast medium with first-pass renal exposure, no case of lactic acidosis was observed based on present data, but further evidence is needed to make a strong suggestion regarding its safety.