Biguanides
The biguanide class of drugs — Glucophage (metformin), Glucophage XR (metformin hydrochloride, extended release), and Riomet (liquid metformin) — is one of the most widely prescribed for type 2 diabetes. Biguanides are often preferred over sulfonylureas because they don't cause hypoglycemia nor do they promote weight gain. They have also been shown to have a positive effect on blood lipid levels.
Metformin is usually taken two to three times daily with meals. The extended release version is designed for once-a-day use, usually with an evening meal. It may also be used in conjunction with a sulfonylurea drug (the combination drug Glucovance is metformin and glyburide) or with insulin therapy.
How They Work
Metformin works by suppressing the amount of glucose your liver pumps out, and consequently reduces the amount of insulin produced by the body. The drug also increases liver, muscle, and fat sensitivity to insulin. Metformin does not promote weight gain (as some type 2 drugs do) and may improve cholesterol profiles in some patients.
Fact
A study at the Hospital for Sick Children and the University of Toronto found that treatment with metformin lowered A1C levels and decreased the need for insulin in teens with type 1 diabetes who were considered to be in poor control of their diabetes.
Possible Side Effects
Metformin is contraindicated, or not recommended, in many people with kidney or liver problems due to the risk of lactic acidosis, a rare but potentially fatal buildup of lactic acid in the bloodstream that occurs when the kidneys do not adequately remove lactic acid. Your doctor can advise you whether the drug is appropriate for you if you have kidney or liver impairment.
Signs of lactic acidosis include weakness, fatigue, dizziness, breathing problems, and unexplained muscle and/or stomach pain. If you experience any of these symptoms while taking metformin and suspect lactic acidosis, call your doctor immediately or go to the nearest emergency care facility.
Alert
If you are undergoing any radiographic (i.e., x-ray or CT scan) procedure that involves injection of a contrast medium (dye) that contains iodine, you should stop taking metformin temporarily because of the risk of lactic acidosis. Metformin can be started again if kidney function is normal when reassessed forty-eight hours after the injection.
Biguanides are also not recommended for use in patients with congestive heart failure. Other potential side effects of metformin include the following:
Gastrointestinal distress (gas and diarrhea)
Nausea
Metallic taste in the mouth
Depletion of vitamin B
12 levels
Because up to 30 percent of patients prescribed metformin experience gastrointestinal discomfort, dosage is generally started quite low and slowly increased.
