Metformin Management Before Surgery

Introduction to Metformin Management

• The American College of Cardiology and other guideline societies recommend stopping metformin the night before surgery and not restarting until 48 hours after surgery, after confirming adequate renal function 1, 2

Rationale for Stopping Metformin

• Metformin is associated with a risk of lactic acidosis, which is a rare but serious complication with mortality rates of 30-50% 1
• The plasma half-life of metformin is 6.2 hours, which means stopping the night before surgery allows for significant clearance 3, 4

Risk Factors for Metformin-Associated Lactic Acidosis

• Renal impairment (creatinine clearance <60 mL/min) is the primary risk factor for metformin-associated lactic acidosis 1, 5
• Administration of iodinated contrast agents is a risk factor for metformin-associated lactic acidosis 3, 4
• Severe heart failure (left ventricular ejection fraction <30%) is a risk factor for metformin-associated lactic acidosis 1

Timing of Metformin Discontinuation

• For patients with normal renal function, the American College of Cardiology recommends stopping metformin the night before surgery 1, 2
• For emergency surgery, the American Heart Association recommends proceeding with surgery but monitoring lactate levels and renal function closely 6

Perioperative Management Algorithm

• The European Society of Cardiology recommends checking renal function (eGFR) before surgery and identifying patients at high risk for lactic acidosis (renal impairment, heart failure, etc.) 1
• The American College of Cardiology recommends waiting 48 hours after major surgery to restart metformin, and confirming adequate renal function before restarting 1, 4

Recent Evidence on Metformin Continuation

• The 2024 AHA/ACC guideline notes that recent data suggest metformin is not associated with lactic acidosis as previously feared 6

Special Considerations for SGLT2 Inhibitors

• The American Heart Association recommends discontinuing SGLT2 inhibitors 3-4 days before surgery due to risk of euglycemic diabetic ketoacidosis 6
• The American Heart Association recommends not restarting SGLT2 inhibitors until the patient is clinically stable and has resumed a normal diet 6

Restarting Metformin After Surgery

Key Requirements and Considerations

• The American Society of Anesthesiologists recommends restarting metformin 2 days (48 hours) after surgery if the patient is eating well and has confirmed adequate renal function, with an estimated glomerular filtration rate (eGFR) of ≥60 mL/min/1.73m² 7
• For major surgery, guidelines mandate waiting 48 hours before restarting metformin, even with normal renal function, due to the risk of lactic acidosis, which occurs in 2-9 cases per 100,000 patients/year with 30-50% mortality 7
• Surgery can cause transient renal impairment that may not be immediately apparent, and perioperative hemodynamic instability increases metformin accumulation risk 7
• Dehydration, ongoing vasopressor requirement, acute heart failure, sepsis, and respiratory insufficiency are conditions where metformin should not be restarted at 48 hours, even if renal function appears normal 7

Perioperative Management of SGLT2 Inhibitors and Metformin

Introduction to Perioperative Management

• The American Heart Association and American College of Cardiology recommend stopping Synjardy at least 3 days before surgery due to the empagliflozin component, and holding metformin the night before surgery 8, 9

Timing of Discontinuation

• Discontinue empagliflozin 3-4 days before surgery to reduce the risk of perioperative euglycemic diabetic ketoacidosis (DKA), a serious and potentially life-threatening complication 8, 9
• Stop metformin the night before surgery, as recommended by the 2024 AHA/ACC guidelines and American Diabetes Association 8, 9

Practical Algorithm for Discontinuation

• For elective surgery, stop Synjardy 3-4 days before surgery, check renal function, assess volume status, monitor blood glucose, and consider reducing basal insulin by 25% the evening before surgery 8, 9
• Use basal-bolus insulin coverage perioperatively, as it improves outcomes compared to reactive sliding scale alone 9

Special Considerations

• The 2024 AHA/ACC guidelines note that recent data suggest metformin may not be as strongly associated with lactic acidosis as previously feared, but the conservative approach of holding it perioperatively remains standard practice 8

Perioperative Management of Synjardy

Introduction to Perioperative Care

• The American College of Cardiology supports stopping metformin the night before surgery for patients with normal renal function, allowing adequate drug clearance given metformin's plasma half-life 10

Risk of Lactic Acidosis from Metformin

• Metformin-associated lactic acidosis occurs in 2-9 cases per 100,000 patients/year but carries a 30-50% mortality rate, with risk factors including renal impairment, severe heart failure, dehydration, and concomitant use of certain medications 10

Special Considerations for High-Risk Patients

• Elderly patients taking high doses of metformin are at increased risk for metformin-associated lactic acidosis 10