Pharmacy Author: Omudhome Ogbru, PharmD
Medical and Pharmacy Editor: Jay W. Marks, MD

GENERIC NAME: metformin

BRAND NAME: Glucophage, Glucophage XR, Glumetza, Fortamet, Riomet

DRUG CLASS AND MECHANISM: Metformin is an oral medication that lowers blood glucose (sugar) and is used for treating type 2 diabetes. Insulin is a hormone produced by the pancreas that controls glucose levels in blood by reducing the amount of glucose made by the liver and by increasing the removal of glucose from the blood by muscle and fat tissues. As a result, blood glucose levels fall. Diabetes caused by a decrease in production of insulin that causes increased production of glucose by the liver, and reduced uptake (and effects) of insulin on fat and muscle tissues. Metformin acts by increasing the sensitivity of liver, muscle, fat, and other tissues to the uptake and effects of insulin. These actions lower the level of sugar in the blood.

Unlike glucose-lowering drugs of the sulfonylurea class, for example glyburide (Micronase; DiaBeta) or glipizide (Glucotrol), metformin does not increase the concentration of insulin in the blood and, therefore, does not cause excessively low blood glucose levels (hypoglycemia) when used alone. In scientific studies, metformin reduced the complications of diabetes such as heart disease, blindness and kidney disease. Metformin was approved by the FDA in December 1994.

PRESCRIPTION: Yes

GENERIC AVAILABLE: Yes

PREPARATIONS: Tablets: 500, 850, and 1000 mg. Tablets (extended release): 500, 750, and 1000 mg. Solution: 500 mg/5 ml

STORAGE: Metformin should be stored at room temperature between 20-25°C (68-77°F).

PRESCRIBED FOR: Metformin is used for treating type 2 diabetes in adults and children. It may be used alone or in combination with other diabetic medications. Metformin also has been used to prevent the development of diabetes in people at risk for diabetes, treatment of polycystic ovaries, and weight gain due to medications used for treating psychoses.

DOSING: For treating type 2 diabetes in adults, metformin (immediate release) usually is begun at a dose of 500 mg twice a day or 850 mg once daily. The dose is gradually increased by 500 mg weekly or 850 mg every two weeks as tolerated and based on the response of the levels of glucose in the blood. The maximum daily dose is 2550 mg given in three divided doses. If extended tablets are used, the starting dose is 500 mg or 1000 mg daily with the evening meal. The dose can be increased by 500 mg weekly up to a maximum dose of 2000 mg (2500 mg of Fortamet) once daily or in two divided doses. Glumetza tablets are given once daily. Metformin should be taken with meals.

For pediatric patients 10-16 years of age, the starting dose is 500 mg twice a day. The dose can be increased by 500 mg weekly up to a maximum dose of 2000 mg. Glucophage XR has not been studied in children.

DRUG INTERACTIONS: Cimetidine (Tagamet), by decreasing the elimination of metformin from the body, can increase the amount of metformin in the blood by 40%. This may increase the frequency of side effects from metformin.

PREGNANCY: There are no adequate studies in pregnant women. Most experts agree that insulin is the best treatment for pregnant women with diabetes.

NURSING MOTHERS: Metformin is excreted into breast milk and can therefore be transferred to the nursing infant. Nursing mothers should not use metformin.

SIDE EFFECTS: The most common side effects with metformin are nausea, vomiting, gas, bloating, diarrhea and loss of appetite. These symptoms occur in one out of every three patients. These side effects may be severe enough to cause therapy to be discontinued in one out of every 20 patients. These side effects are related to the dose of the medication and may decrease if the dose is reduced.

A serious but rare side effect of metformin is lactic acidosis. Lactic acidosis occurs in one out of every 30,000 patients and is fatal in 50% of cases. The symptoms of lactic acidosis are weakness, trouble breathing, abnormal heartbeats, unusual muscle pain, stomach discomfort, light-headedness and feeling cold. Patients at risk for lactic acidosis include those with reduced function of the kidneys or liver, congestive heart failure, severe acute illnesses, and dehydration.

From the Doctors at MedicineNet.com

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