Short answer: Sometimes. The metformin label says to stop it at or before an iodinated contrast scan in people with an eGFR of 30 to 60, liver disease, alcoholism or heart failure, or when the dye goes into an artery, then recheck eGFR 48 hours later and restart if kidney function is stable. For surgery, it says to pause metformin while food and fluids are restricted.
Section 2.4 of the metformin label, "Discontinuation for Iodinated Contrast Imaging Procedures," says to stop metformin at the time of, or before, an iodinated contrast imaging procedure in these groups:
It then says to re-evaluate eGFR 48 hours after the scan and restart metformin if kidney function is stable. Iodinated contrast is the dye used in many CT scans and angiograms. The label does not set a stop rule for people outside these groups.
Section 5.1 explains the reason. Giving iodinated contrast into a vein or artery in people taking metformin has led to a sudden drop in kidney function and to lactic acidosis, a buildup of acid in the blood. Metformin is cleared by the kidneys, so if they slow down, it can build up.
The label's boxed warning lists contrast scans, surgery and other procedures among the risk factors for metformin-associated lactic acidosis, alongside kidney impairment, age 65 or older, heavy alcohol use, liver impairment and low-oxygen states such as acute heart failure. Metformin is contraindicated when eGFR is below 30 (section 4).
For surgery, section 5.1 says that withholding food and fluids during surgical or other procedures may raise the risk of volume depletion, low blood pressure and kidney impairment, and that metformin should be temporarily stopped while food and fluid intake is restricted.
The patient counseling section asks prescribers to tell patients to let their doctor know they take metformin before any surgical or radiological procedure, since a temporary stop may be needed. The plan for when to stop and restart comes from the prescriber and the team doing the procedure.
The MedlinePlus metformin page gives the patient-facing version: tell the doctor about metformin before any surgery, including dental surgery, or an x-ray procedure with injected dye, and expect that you may need to stop before the procedure and wait at least 48 hours to restart, with the doctor saying exactly when.
| Situation | What the label says |
|---|---|
| Iodinated contrast, eGFR 30 to 60 | Stop at the time of or before the scan (section 2.4) |
| Iodinated contrast, liver disease, alcoholism or heart failure | Stop at the time of or before the scan (section 2.4) |
| Contrast into an artery | Stop at the time of or before the scan (section 2.4) |
| After the scan | Recheck eGFR at 48 hours; restart if kidney function is stable |
| Surgery with food and fluids held | Temporarily stop while intake is restricted (section 5.1) |
| eGFR below 30 | Contraindicated (section 4) |
A recent eGFR result, the metformin dose and the time of the last tablet are useful to bring to the pre-scan or pre-surgery check. Dose Track can log each tablet and keep your kidney results alongside it.
Read more on Dose Track: Metformin side effects · Metformin guide · Lactic acidosis (glossary) · eGFR (glossary) · Missed a dose of metformin · Metformin vs Jardiance