Is Routine Metformin Discontinuation Necessary Before Elective Coronary Angiography? A Randomized Clinical Trial

Background: The optimal peri-procedural management of metformin in patients with type 2 diabetes undergoing elective coronary angiography remains debated. Concerns regarding contrast-induced acute kidney injury (CI-AKI) and the potential risk of metformin-associated lactic acidosis (MALA) have led to varying clinical practices, despite evolving evidence. Furthermore, limited data exist regarding the influence of metformin dosage and baseline renal function on post-procedural renal and metabolic outcomes. This randomized clinical trial aimed to evaluate the safety of continuing metformin therapy during elective coronary angiography and to assess the impact of metformin dose and pre-procedural renal status on subsequent laboratory changes. Methods: In this prospective, open-label randomized study, 204 adults with type 2 diabetes receiving metformin and scheduled for elective coronary angiography at Heshmat Hospital, Rasht, Iran, were randomly assigned to either continue metformin therapy (n = 102) or discontinue metformin 24 hours before the procedure with resumption 72 hours afterward (n = 102). Serum creatinine, estimated glomerular filtration rate (eGFR), plasma lactate concentration, and arterial pH were assessed at baseline and 72 hours following angiography. Between-group comparisons were conducted using appropriate statistical tests. Multivariable regression analysis was performed to adjust for baseline laboratory values, metformin dose, contrast volume, age, body mass index, and sex. Results: No statistically significant differences were observed between the continuation and discontinuation groups in post-procedural serum creatinine, eGFR, lactate levels, or arterial pH (all P > 0.05). Baseline renal and metabolic parameters were the strongest predictors of post-angiography values. Higher daily metformin doses (1500–2000 mg) were associated with modest increases in serum creatinine and lactate; however, these changes were not clinically significant and were not accompanied by meaningful alterations in arterial pH. Conclusion: Among patients with type 2 diabetes and preserved renal function undergoing elective coronary angiography, continuation of metformin therapy did not increase the risk of CI-AKI or clinically relevant metabolic disturbances. These findings support an individualized approach to peri-procedural metformin management rather than routine discontinuation.