Mode of Action
Decreases hepatic gluconeogenesis, decreases glucose absorption in the intestines, and increases sensitivity to insulin by increasing peripheral glucose uptake and utilization.
Known hypersensitivity to the metformin, or any component of the formulation. Renal disease (males with serum creatinine >1.5 mg/dL, females with serum creatinine >1.4 mg/dL). Metformin should be held 48 hours before and 48 hours after any radiologic procedure where iodinated contrast material is administered. It should also be held in the case of acute MI, CHF exacerbation, surgery, or shock. It may be restarted once good renal function is confirmed. In emergent situations, ensure adequate hydration and monitor renal function closely. Acute or chronic metabolic acidosis (including ketoacidosis). Pregnancy Category: B.
Gastrointestinal symptoms are very common (at least 30% of patients) and generally dose related. Metformin should be started at low doses and gradually titrated to minimize GI effects.
Low B12 levels. This should be checked every two to three years.
Metallic taste in mouth (3%).
Lactic acidosis is very rare (0.03 cases/1,000 patient-years), but is fatal in 50% of cases.
Acute or chronic alcohol use increases the risk for lactic acidosis. Azole antifungal agents, levofloxacin, and monoamine oxidase inhibitors may increase the risk for hypoglycemia. Nifedipine may enhance metformin absorption. Cationic drugs (amiloride, cimetidine, cotrimoxazole, digoxin, dofetilide, morphine, procainamide, quinidine, quinine, ranitidine, triamterene, and vancomycin) increase the risk for lactic acidosis by interfering with the renal tubular transport of metformin.
Metformin can be taken with meals to minimize GI upset.
Metformin (Glucophage, Glucophage XR).
Usual starting dose: Immediate release, 500 mg BID with meals, or 850 mg QD with breakfast. Extended release, 500 mg QPM with evening meal.
Usual maintenance doses: Immediate release, 1,500-2,550 mg/day in divided doses with meals. Extended release, 500-2,000 mg QPM with evening meal (2,000 mg dose may be divided into 1,000 mg BID).
Dosage Forms Available
500 mg and 850 mg immediate release tablets, and 500 mg extended release tablets.
Other Points of Interest
Metformin, when used as monotherapy, does not cause hypoglycemia unless the patient does not have a sufficient caloric intake, exercises vigorously and does not consume adequate calories, or drinks alcohol.
Hutchison TA, Shahan DR, Anderson ML (eds): DRUGDEX System. MICROMEDEX, Inc, Englewood, Colo. (Edition expires 12/2000)
Hebel SK, Katstrup EK (eds): Drug Facts and Comparisons. St. Louis, Mo. 2001
South Med J. 2002;95(1) © 2002 Lippincott Williams & Wilkins
Cite this: Medication Update - Medscape - Jan 01, 2002.