How long to hold Metformin (metformin) before an abdominal contrast Computed Tomography (CT) scan in patients with Impaired renal function?

From the Guidelines

Metformin should be held for at least 48 hours after receiving intravenous contrast for an abdominal CT scan, and it is recommended to stop taking metformin 48 hours before the scheduled CT scan with contrast and not resume it until 48 hours after the procedure, as stated in the most recent and highest quality study 1. This precaution is necessary because contrast dye can temporarily affect kidney function, and metformin is cleared by the kidneys. If kidney function becomes impaired while metformin is in your system, there's a small risk of developing lactic acidosis, a rare but serious condition. Some key points to consider include:

• The risk of lactic acidosis is increased in patients with renal failure, and metformin should preferably be stopped before the procedure in these cases, as noted in 1.
• Checking renal function after angiography in patients on metformin and withholding the drug when renal function deteriorates might be an acceptable alternative to automatic suspension of metformin, as suggested in 1.
• Kidney function should be reassessed before treatment is restarted, as recommended in 1.
• The plasma half-life of metformin is 6.2 hours, but there is no convincing evidence for a specific recommendation on when to stop metformin before angiography or PCI, as stated in 1. It is essential to follow the specific instructions provided by your doctor or radiology department, as facilities may have different protocols, with holding periods ranging from 24-48 hours. If you have existing kidney problems, your doctor might recommend a longer period of withholding metformin or may consider alternative imaging approaches.

From the FDA Drug Label

Radiologic studies with contrast —Administration of intravascular iodinated contrast agents in metformin-treated patients has led to an acute decrease in renal function and the occurrence of lactic acidosis. Stop metformin hydrochloride tablets at the time of, or prior to, an iodinated contrast imaging procedure in patients with an eGFR between 30 and 60 mL/min/1. 73 m 2; in patients with a history of hepatic impairment, alcoholism or heart failure; or in patients who will be administered intra-arterial iodinated contrast. Re-evaluate eGFR 48 hours after the imaging procedure, and restart metformin hydrochloride tablets if renal function is stable

The metformin should be stopped at the time of, or prior to, the iodinated contrast imaging procedure, and can be restarted 48 hours after the imaging procedure if renal function is stable 2.

From the Research

Metformin and Contrast CT

• The risk of lactic acidosis in patients taking metformin who undergo contrast CT is low, especially in those with normal renal function 3, 4.
• Studies have shown that the incidence of contrast-induced nephropathy (CIN) in diabetic patients without prior renal failure is minimal, and recommendations to stop metformin may be restricted to patients with abnormal renal function 4.
• A systematic review of guidelines found substantial inconsistencies in recommendations regarding metformin usage with contrast medium administration, with most guidelines having poor scores on objective assessment of rigor of guideline development 5.

Duration of Metformin Discontinuation

• One study suggests that metformin does not need to be discontinued before or after intravenous contrast medium exposure in patients with an estimated glomerular filtration rate (eGFR) > 30 mL/min/1.73 m2 6.
• Another study recommends withholding metformin for 48 hours after contrast medium administration, during which time contrast-induced renal failure becomes clinically apparent, and restarting metformin if renal function is normal at 48 hours 7.
• However, there is no scientific justification for withholding metformin for 48 hours before administration of the contrast medium, as currently recommended in the package insert 7.

Key Considerations

• Patients with abnormal renal function or those receiving intra-arterial contrast medium with first-pass renal exposure may require special consideration, and further evidence is needed to make strong suggestions regarding the safety of continuing metformin in these cases 6.
• The risk of lactic acidosis is low, but patients should be aware of the potential risks and benefits of continuing or discontinuing metformin during contrast CT, and healthcare providers should carefully evaluate individual patient factors when making decisions about metformin use 3, 6.