Is metformin (biguanide oral hypoglycemic agent) held on the day of surgery?

Metformin Management on the Day of Surgery

Metformin should be held the night before surgery and not restarted until 48 hours after surgery, after confirming adequate renal function. 1, 2

Rationale for Withholding Metformin

• Metformin is associated with a risk of lactic acidosis, a rare but serious complication with mortality rates of 30-50% 2, 1
• The FDA label specifically recommends temporary discontinuation of metformin for surgical procedures due to increased risk of lactic acidosis 3
• Surgery and the perioperative period create conditions that increase the risk of lactic acidosis, including:
  • Restricted food and fluid intake 3
  • Potential hemodynamic instability 2
  • Risk of acute kidney injury 2
  • Hypoxic states that may occur during surgery 3

Timing of Metformin Discontinuation

• For elective surgery, metformin should be stopped the night before surgery 2, 1
• The plasma half-life of metformin is approximately 6.2 hours, allowing for significant clearance when stopped the night before 1
• Patients should be instructed to inform their healthcare providers that they are taking metformin prior to any surgical procedure 3

Risk Factors for Metformin-Associated Lactic Acidosis

• Pre-existing renal impairment (creatinine clearance <60 mL/min) 2, 3
• Severe heart failure (left ventricular ejection fraction <30%) 2, 1
• Dehydration, which can occur during the perioperative period 3
• Administration of iodinated contrast agents 2, 1
• Conditions associated with hypoxemia that may occur during surgery 3

Postoperative Metformin Management

• Do not restart metformin until 48 hours after major surgery 2, 1
• Confirm adequate renal function before restarting metformin 2, 1, 3
• For minor or ambulatory surgery, metformin may be continued except in cases of severe renal failure 2

Recent Evidence on Metformin Continuation

• Some recent studies suggest that the risk of lactic acidosis with perioperative metformin use may be lower than previously thought 4, 5
• A randomized controlled trial found that continuation of metformin during elective non-cardiac surgery did not significantly raise lactate levels to a clinically relevant degree 4
• However, despite these findings, current guidelines and the FDA label still recommend withholding metformin before surgery 1, 3

Special Considerations

• Emergency surgery: If metformin cannot be stopped in advance, monitor lactate levels and renal function closely 1
• Patients with normal renal function have lower risk, but metformin should still be held according to guidelines 1, 3
• The "sick-day rules" for metformin apply to the perioperative period - temporarily discontinue metformin when there is increased risk of acute kidney injury 2

Despite some emerging evidence suggesting lower risk, the consensus from guidelines and FDA recommendations is clear: metformin should be held before surgery to minimize the risk of lactic acidosis, with restart only after confirming stable renal function postoperatively.