How long should metformin (biguanide oral hypoglycemic) be held before and after surgery in patients with normal renal function?

From the Guidelines

Metformin should be held on the day of surgery and resumed 48 hours after surgery in patients with normal renal function, as recommended by the most recent guidelines 1. The decision to hold metformin before and after surgery is based on the risk of lactic acidosis, a rare but serious side effect of metformin.

• The risk of lactic acidosis is increased in patients with renal failure, and surgery can temporarily compromise renal function, leading to metformin accumulation.
• The guidelines recommend holding metformin on the day of surgery and resuming it 48 hours after surgery, once normal renal function has been confirmed and the patient is eating and drinking adequately.
• Alternative glucose management during the perioperative period typically involves insulin therapy as needed, with regular blood glucose monitoring.
• The target range for blood glucose in the perioperative period should be 100-180 mg/dL (5.6-10.0 mmol/L) within 4 hours of surgery, as recommended by the guidelines 1. Some key points to consider when managing metformin in the perioperative period include:
• Monitoring blood glucose at least every 2-4 hours while the patient is taking nothing by mouth and dosing with short- or rapid-acting insulin as needed.
• Avoiding stricter perioperative glycemic goals, as they may not improve outcomes and are associated with more hypoglycemia 1.
• Considering a reduction of basal insulin by 25% the evening before surgery to achieve perioperative blood glucose goals with a lower risk for hypoglycemia 1.

From the Research

Metformin Hold Times Before and After Surgery

• The ideal time to hold metformin before and after surgery is not explicitly stated in the provided studies, but we can gather information about the risks associated with metformin and lactic acidosis.
• Metformin is mainly cleared by the kidneys, with an apparent clearance of 933-1317 ml/min and a half-life of less than 3 hours 2.
• Lactic acidosis is a rare but potentially fatal complication associated with metformin use, and it is often caused by preventable drug accumulation 2, 3, 4.
• The risk of lactic acidosis is higher in patients with renal impairment, sepsis, fever, diarrhea, vomiting, and other conditions that reduce metformin renal clearance 2, 5, 6.
• In patients with normal renal function, the risk of lactic acidosis is lower, but it is still important to monitor patients closely and adjust metformin doses accordingly 5, 6.
• There is no clear consensus on the exact time to hold metformin before and after surgery, but it is generally recommended to discontinue metformin 24-48 hours before surgery and restart it when renal function is normalized and the patient is hemodynamically stable 2.
• However, the provided studies do not give a specific time frame for holding metformin before and after surgery, and the decision to hold metformin should be made on a case-by-case basis, taking into account the patient's individual risk factors and medical history.

Key Considerations

• Patients should be aware that discontinuation of metformin for a limited time does not affect their health, but it may avoid a serious, potentially fatal adverse event 2.
• The role of metformin in lactic acidosis is still debated, and more research is needed to fully understand the relationship between metformin and lactic acidosis 3, 4.
• Diabetes rather than metformin therapy is the major risk factor for the development of lactic acidosis 5.
• Alcohol abuse and its effects on health seem to be the main cause of lactic acidosis in diabetic patients 6.