Metformin (Glucophage) is currently the only biguanide oral antidiabetic drug. It works by inhibiting hepatic glucose production and increasing the sensitivity of peripheral tissue to insulin. Because its mechanism of action differs from that of sulfonylurea drugs, it may be given along with these drugs.
Metformin use is contraindicated in patients with a known hypersensitivity to biguanides, hepatic or renal disease, alcoholism, or cardiopulmonary disease.
With biguanides, be aware that older adult or malnourished patients may react adversely to this group of drugs. Contraindications, cautions, and interactions for this drug have been previously discussed, but it is important to patient safety to emphasize the interaction between metformin and the iodine-containing radiologic contrast media used for certain diagnostic purpose. This interaction is associated with an increased risk for acute renal failure and lactic acidosis. If the patient is taking metformin, closely assess and monitor for this scenario so that the metformin may be discontinued on the day of the test and for at least 48 hours afterward.