metformin

Generic Name: metformin (met FOR min)
Brand Names: Fortamet, Glucophage, Glucophage XR, Glumetza, Riomet

What is metformin?

Metformin is an oral diabetes medicine that helps control blood sugar levels.

Metformin is for people with type 2 diabetes. Metformin is sometimes used in combination with insulin or other medications, but it is not for treating type 1 diabetes.

Metformin may also be used for purposes not listed in this medication guide.

What is the most important information I should know about metformin?

You should not use this medication if you are allergic to metformin, or if you are in a state of diabetic ketoacidosis (call your doctor for treatment with insulin).

If you need to have any type of x-ray or CT scan using a dye that is injected into your veins, you will need to temporarily stop taking metformin.

Before taking metformin, tell your doctor if you have liver disease or a history of heart disease.

Some people develop lactic acidosis while taking metformin. Early symptoms may get worse over time and this condition can be fatal. Get emergency medical help if you have even mild symptoms such as: muscle pain or weakness, numb or cold feeling in your arms and legs, trouble breathing, stomach pain, nausea with vomiting, slow or uneven heart rate, dizziness, or feeling very weak or tired.

What should I discuss with my healthcare provider before taking metformin?

Some people develop a life-threatening condition called lactic acidosis while taking metformin. You may be more likely to develop lactic acidosis if you have liver or kidney disease, congestive heart failure, a severe infection, if you are dehydrated, or if you drink large amounts of alcohol. Talk with your doctor about your individual risk. You should not use this medication if you are allergic to metformin, or if you are in a state of diabetic ketoacidosis (call your doctor for treatment with insulin).

If you need to have any type of x-ray or CT scan using a dye that is injected into your veins, you will need to temporarily stop taking metformin.

To make sure you can safely take metformin, tell your doctor if you have any of these other conditions:

• liver disease; or

• a history of heart disease.

FDA pregnancy category B. This medication is not expected to be harmful to an unborn baby. Tell your doctor if you are pregnant or plan to become pregnant during treatment. It is not known whether metformin passes into breast milk or if it could harm a nursing baby. You should not breast-feed while you are using metformin. Metformin should not be given to a child younger than 10 years old. Extended-release metformin (Glucophage XR) should not be given to a child younger than 17 years old.

How should I take metformin?

Take exactly as prescribed by your doctor. Do not take in larger or smaller amounts or for longer than recommended. Follow the directions on your prescription label. Your doctor may occasionally change your dose to make sure you get the best results.

Take metformin with a meal, unless your doctor tells you otherwise. Some forms of metformin are taken only once daily with the evening meal. Follow your doctor's instructions.

Metformin is only part of a complete program of treatment that also includes diet, exercise, and weight control. It is important to use this medicine regularly to get the most benefit. Get your prescription refilled before you run out of medicine completely.

Do not crush, chew, or break an extended-release tablet (Glucophage XR). Swallow the pill whole. Breaking the pill may cause too much of the drug to be released at one time.

Your blood sugar will need to be checked often, and you may need other blood tests at your doctor's office. Visit your doctor regularly.

Check your blood sugar carefully during a time of stress or illness, if you travel, exercise more than usual, drink alcohol, or skip meals. These things can affect your glucose levels and your dose needs may also change.

Your doctor may want you to stop taking metformin for a short time if you become ill, have a fever or infection, or if you have surgery or a medical emergency.

Ask your doctor how to adjust your metformin dose if needed. Do not change your medication dose or schedule without your doctor's advice.

Your doctor may have you take extra vitamin B12 while you are taking metformin. Take only the amount of vitamin B12 that your doctor has prescribed.

Store at room temperature away from moisture, heat, and light.

See also: Metformin dosage (in more detail)

What happens if I miss a dose?

Take the missed dose as soon as you remember (be sure to take the medicine with food). Skip the missed dose if it is almost time for your next scheduled dose. Do not take extra medicine to make up the missed dose.

What happens if I overdose?

Seek emergency medical attention or call the Poison Help line at 1-800-222-1222. An overdose of metformin may cause lactic acidosis. Get emergency medical help if you have any of these symptoms of lactic acidosis: weakness, increasing sleepiness, slow heart rate, cold feeling, muscle pain, shortness of breath, stomach pain, feeling light-headed, and fainting.

What should I avoid while taking metformin?

Avoid drinking alcohol. It lowers blood sugar and may increase your risk of lactic acidosis while taking metformin.

Metformin side effects

Get emergency medical help if you have any of these signs of an allergic reaction: hives; difficult breathing; swelling of your face, lips, tongue, or throat. This medication may cause lactic acidosis (a build-up of lactic acid in the body, which can be fatal). Lactic acidosis can start slowly and get worse over time. Get emergency medical help if you have even mild symptoms of lactic acidosis, such as:

• muscle pain or weakness;

• numb or cold feeling in your arms and legs;

• trouble breathing;

• feeling dizzy, light-headed, tired, or very weak;

• stomach pain, nausea with vomiting; or

• slow or uneven heart rate.

Call your doctor at once if you have any other serious side effect such as:

• feeling short of breath, even with mild exertion;

• swelling or rapid weight gain; or

• fever, chills, body aches, flu symptoms.

Less serious side effects may include:

• headache or muscle pain;

• weakness; or

• mild nausea, vomiting, diarrhea, gas, stomach pain.

This is not a complete list of side effects and others may occur. Call your doctor for medical advice about side effects. You may report side effects to FDA at 1-800-FDA-1088.

See also: metformin side effects (in more detail)

Metformin Dosing Information

Usual Adult Dose for Diabetes Mellitus Type II:

500 mg orally twice a day (with the morning and evening meal)

Extended Release:
500 to 2000 mg orally once a day (with the evening meal). Maximum daily dose is 2500 mg.

Usual Pediatric Dose for Diabetes Mellitus Type II:

10 years of age and older:
Immediate-release tablets: 500 mg orally twice a day (with the morning and evening meal). Dosage increases should be made in increments of 500 mg weekly up to a maximum of 2000 mg per day, given in divided doses.

Safety and effectiveness of metformin extended-release has not been established in pediatric patients (less than 18 years of age).

500 mg twice a day, given with meals.

What other drugs will affect metformin?

Tell your doctor about all other medicines you use, especially:

• furosemide (Lasix);

• nifedipine (Adalat, Procardia);

• cimetidine (Tagamet) or ranitidine (Zantac);

• amiloride (Midamor) or triamterene (Dyrenium);

• digoxin (Lanoxin);

• morphine (MS Contin, Kadian, Oramorph);

• procainamide (Procan, Pronestyl, Procanbid);

• quinidine (Quin-G) or quinine (Qualaquin);

• trimethoprim (Proloprim, Primsol, Bactrim, Cotrim, Septra); or

• vancomycin (Vancocin, Lyphocin).

You may be more likely to have hyperglycemia (high blood sugar) if you take metformin with other drugs that can raise blood sugar, such as:

• isoniazid;

• diuretics (water pills);

• steroids (prednisone and others);

• heart or blood pressure medication (Cartia, Cardizem, Covera, Isoptin, Verelan, and others);

• niacin (Advicor, Niaspan, Niacor, Simcor, Slo-Niacin, and others);

• phenothiazines (Compazine and others);

• thyroid medicine (Synthroid and others);

• birth control pills and other hormones;

• seizure medicines (Dilantin and others); and

• diet pills or medicines to treat asthma, colds or allergies.

These lists are not complete and other drugs may interact with metformin. Tell your doctor about all medications you use. This includes prescription, over-the-counter, vitamin, and herbal products. Do not start a new medication without telling your doctor.

Where can I get more information?

• Your pharmacist can provide more information about metformin.