Metformin Pre-Surgery Hold Window: When to Stop and When to Restart

What the label says about surgery

Metformin is a biguanide cleared by the kidneys [1]. The immediate-release tablet label [1] and the extended-release tablet label [2] carry the same wording on the points below. Both list surgery and other procedures as risk factors for metformin-associated lactic acidosis, the boxed-warning risk that has resulted in death, hypothermia, hypotension and resistant bradyarrhythmias [1][2].

Both labels say metformin should be temporarily discontinued while patients have restricted food and fluid intake. They say withholding food and fluids during surgery or other procedures may increase the risk of volume depletion, hypotension and renal impairment [1][2]. They also say postmarketing cases of lactic acidosis primarily occurred in patients with significant renal impairment [1][2].

Contrast procedures: the explicit timed rule

For iodinated contrast, the label gives a specific rule. It says to stop metformin at the time of or before the procedure in patients with eGFR 30 to 60 mL/min/1.73 m², a history of hepatic impairment, alcoholism or heart failure, or when intra-arterial iodinated contrast will be used [1][2]. It says to re-evaluate eGFR 48 hours after the procedure and restart metformin if renal function is stable [1][2].

Renal function and the eGFR cutoffs

The label says to obtain an eGFR before starting metformin and at least yearly thereafter [1][2]. Metformin is contraindicated below 30 mL/min/1.73 m², starting is not recommended at 30 to 45, and if eGFR falls below 45 the label says to reassess benefit and risk; it says to discontinue if eGFR falls below 30 [1][2]. Age 65 or older is another listed risk factor, and the label says to assess renal function more frequently in elderly patients [1][2].

If lactic acidosis is suspected

The label says to discontinue metformin immediately and institute general supportive measures in a hospital setting; prompt hemodialysis is recommended [1][2]. Symptoms named in the boxed warning include malaise, myalgias, respiratory distress, somnolence and abdominal pain, and the onset is often subtle [1][2].