Peri‐operative continuation of metformin does not improve glycaemic control in patients with type 2 diabetes: A randomized controlled trial

Historically, metformin was withheld before surgery in fear of metformin associated lactic acidosis. Now, this risk is deemed low and guidelines move towards continuation of metformin. We hypothesized that continuing metformin perioperatively would lower postoperative serum glucose without an effect on plasma lactate. We performed a single-blind multicenter RCT in type 2 diabetes mellitus patients scheduled for non-cardiac surgery and continued (MF+) or withheld (MF–) metformin before surgery. Main outcome parameters were the differences in perioperative plasma glucose and lactate levels. We randomized 70 patients (37 MF+ group and 33 MF– group) with type 2 diabetes mellitus. Postoperative glucose levels were similar between groups (148 ± 32 (MF+) vs. 149 ± 41 mg dl-1 (MF–), p=0.95) Although preoperative lactate levels were slightly higher in the MF+ group compared to the MF– group (1.5 vs. 1.2 mmol l-1, p=0.02), the postoperative lactate levels were not significantly different (1.2 vs. 1.0 mmol l-1, p=0.18). In conclusion, continuation of metformin during elective non-cardiac surgery does not improve glucose control or raise lactate levels to a clinically relevant degree. MESH Keywords: Metformin; Diabetes Mellitus, Type 2; Perioperative Period. Trial registry number: NTR5254 Nederlands Trial Register