Metformin

Metformin is an oral antidiabetic medication in the biguanide class used as first-line therapy for type 2 diabetes, particularly in people who are overweight. It lowers blood glucose primarily by reducing hepatic glucose production and by improving insulin sensitivity in muscle. It may also modestly reduce intestinal glucose absorption. Unlike some antidiabetic drugs, metformin does not increase insulin secretion and therefore has a low risk of causing hypoglycemia when used alone.

Metformin is not metabolized by the liver and is excreted unchanged by the kidneys. It is available in immediate-release and extended-release formulations. Common brand names include Glucophage (immediate-release) and Fortamet or Glumetza (extended-release). Dosing is individualized and usually starts with a low amount with meals to minimize gastrointestinal side effects. Typical daily doses for immediate-release range up to about 2000 mg, while extended-release products are commonly given once daily with a target total daily dose in the 2000 mg range, depending on product labeling and patient tolerance.

Common adverse effects are gastrointestinal, including nausea, diarrhea, and abdominal discomfort, often improving with time or with dose adjustments. Long-term use can be associated with vitamin B12 deficiency. A rare but serious risk is lactic acidosis, more likely with renal impairment, liver disease, alcoholism, or hypoxic states. Metformin is contraindicated in severe renal impairment and other conditions associated with acidosis. It should be held around iodinated contrast imaging and restarted only after renal function is reassessed. It is also used off-label for polycystic ovary syndrome in some settings.