• Risk Factors for Metformin
• Renal impairment (delayed excretion of metformin, acidosis). Serum Creatinine >1.3mg/dl for women, >1.4mg/dl for men.
• Excess alcohol use.
• Shock: CHF, sepsis, myocardial infarcts, dehydration.
• Acidosis.
• Major surgery.
• Hypoxia, COPD, pneumonia, asthma.
• Use of iodinated contrast material (stop metformin before study).
• Stop in-hospitalized patients and substitute insulin until discharge.
• Cirrhosis.

Intravascular contrast studies with iodinated materials can lead to acute alteration of renal function and have been associated with lactic acidosis in patients receiving Glucophage® (see Contraindications). Therefore, in patients in whom any such study is planned, Glucophage® should be discontinued at the time of or prior to the procedure and withheld for 48 hours subsequent to the procedure and reinstituted only after renal function has been re-evaluated and found to be normal. (Note the requirement to stop metformin 48 hours before the contrast study has been eliminated).

Because metformin (Glucophage®) is eliminated by the kidney through filtration and tubular secretion, impairment of renal function can lead to persistence of metformin and development of lactic acidosis. Approximately 90 percent of the absorbed drug is eliminated by the renal route within the first 24 hours. Withholding the drug for 48 hours after administration of intravascular iodinated contrast material allows metformin to clear and provides an opportunity to assess any alteration in renal function caused by the administered intravascular contrast.

Update on metformin (Glucophage®) therapy and the risk of lactic acidosis: change in FDA-approved package insert. 
Bush WH, Bettmann MA. 
ACR Bulletin 1998; 54(3): 15.