When is it safe to resume metformin (biguanide oral hypoglycemic) after surgery or anesthesia?

From the Guidelines

Metformin can typically be resumed 48 hours after surgery or anesthesia, once normal oral intake and renal function have been established, as recommended by the most recent guidelines 1. The exact timing may vary based on the patient's clinical status and the type of procedure performed. Before restarting metformin, healthcare providers should confirm that the patient is hemodynamically stable, has resumed adequate oral intake, and has normal kidney function as demonstrated by laboratory tests. For major surgeries or procedures involving contrast media, waiting 48-72 hours may be necessary, considering the risk of lactic acidosis, a rare but serious side effect associated with metformin use, especially in patients with renal impairment or heart failure 1. Patients should resume their pre-surgical dosing schedule unless their physician indicates otherwise. During the period when metformin is held, blood glucose should be monitored regularly, and alternative glucose-lowering strategies such as insulin may be needed to maintain glycemic control, with a target blood glucose range of 100–180 mg/dL (5.6–10.0 mmol/L) in the perioperative period 1. Key considerations for restarting metformin include:

• Confirmation of adequate renal function, with a creatinine clearance of at least 60 mL/min 1
• Absence of risk factors for lactic acidosis, such as severe heart failure or renal failure 1
• Hemodynamic stability and adequate oral intake
• Monitoring of blood glucose levels to guide adjustments in glucose-lowering therapy.

From the FDA Drug Label

Metformin hydrochloride tablets should be temporarily discontinued while patients have restricted food and fluid intake

Surgery and other procedures —Withholding of food and fluids during surgical or other procedures may increase the risk for volume depletion, hypotension, and renal impairment.

In patients taking metformin hydrochloride tablets whose eGFR falls below 45 mL/min/1. 73 m 2, assess the benefit and risk of continuing therapy.

It is recommended to temporarily discontinue metformin hydrochloride tablets in patients who have restricted food and fluid intake, such as during surgery or other procedures. The medication can be restarted when the patient's condition stabilizes and renal function is re-evaluated. However, the exact timing for resuming metformin after surgery or anesthesia is not explicitly stated in the label. Therefore, the decision to resume metformin should be made on a case-by-case basis, taking into account the patient's individual circumstances and renal function 2.

From the Research

Resuming Metformin after Surgery or Anesthesia

• The decision to resume metformin after surgery or anesthesia should be based on the individual patient's condition and the type of surgery performed 3, 4, 5, 6, 7.
• Historically, metformin was withheld before surgery due to the risk of metformin-associated lactic acidosis, but current guidelines suggest that this risk is low and metformin can be continued peri-operatively 3, 7.
• Some studies suggest that metformin can be resumed 3 hours after extubation in patients undergoing coronary artery bypass grafting (CABG) without an increased risk of lactic acidosis 7.
• However, other studies recommend withdrawing metformin 48 hours prior to surgery and waiting until the patient's biological and clinical parameters return to normal before reintroducing it 5.
• The risk of lactic acidosis is higher in patients with renal dysfunction, hepatic failure, or respiratory failure, and metformin should be used with caution in these patients 4, 6.
• Close collaboration with the surgical and endocrinological team is necessary for the management of the postoperative period and planning the reintroduction of metformin in patients undergoing major abdominal surgery 6.

Factors to Consider when Resuming Metformin

• The type and complexity of the surgery performed
• The patient's renal and hepatic function
• The presence of other comorbid conditions, such as cardiovascular or respiratory disease
• The patient's overall clinical condition and stability
• The risk of lactic acidosis and the need for close monitoring of lactate levels and other clinical parameters 3, 4, 5, 6, 7.

Clinical Guidelines

• There are no standardized guidelines for metformin administration during the perioperative period, and published data remain controversial 4.
• However, some studies suggest that metformin can be safely continued peri-operatively in patients with type 2 diabetes undergoing non-cardiac surgery without an increased risk of lactic acidosis 3, 7.
• Further research is needed to establish clear guidelines for the use of metformin in the perioperative period 3, 4, 5, 6, 7.