Medications and Drugs
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.
Reference: FDA Prescribing Information
Last Editorial Review: 1/7/2008
Report Problems to the Food and Drug Administration
You are encouraged to report negative side effects of prescription drugs to the FDA. Visit the FDA MedWatch website or call 1-800-FDA-1088.
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