Metformin (patient information)

IMPORTANT WARNING
Metformin may rarely cause a serious, life-threatening condition called lactic acidosis. Tell your doctor if you have or have ever had a heart attack; stroke; high blood pressure; diabetic ketoacidosis ( blood sugar that is high enough to cause severe symptoms and requires emergency medical treatment) or coma; surgery to remove part of your small intestine; anemia (not enough red blood cells), or heart, kidney, lung, or liver disease.

Tell your doctor if you have recently had any of the following conditions, or if you develop them during treatment: serious infection; severe diarrhea, vomiting, or fever; or if you drink much less fluid than usual for any reason. You may have to stop taking metformin until you recover.

If you are having surgery, including dental surgery, any x-ray procedure in which dye is injected, or any major medical procedure, tell the doctor that you are taking metformin. You may need to stop taking metformin before the procedure and wait 48 hours to restart treatment. Your doctor will tell you exactly when you should stop taking metformin and when you should start taking it again.

Tell your doctor and pharmacist if you are taking or have taken the following medications: acyclovir (Zovirax); acetaminophen (Tylenol); aminoglycoside antibiotics such as amikacin (Amikin), gentamicin (Garamycin), Kanamycin (Kantrex), Neomycin (Neo-Fradin, Neo-Rx), netilmycin (netromycin), paramomycin (Humatin), streptomycin and tobramycin (Nebcin, Tobi); amphotericin B (Abelcet, Amphocin, others); angiotensin converting enzyme (ACE) inhibitors such as benazepril (Lotensin), captopril (Capoten), enalapril (Vasotec), fosinopril (Monopril), lisinopril (Prinvil, Zestril), moexipril (Univasc), perindopril (Aceon), quinapril (Accupril), ramipril (Altace), and trandolapril (Mavik); aspirin and other non-steroidal anti-inflammatory agents (NSAIDs) such as ibuprofen (Advil, Motrin) and naproxen (Aleve, Naprosyn); cancer chemotherapy medications; cyclosporine (Sandimmune, Neoral); dapsone (Avlosulfon); diuretics (water pills); foscarnet (Foscavir); gold compounds such as auranofin (Ridaura), aurothioglucose (Aurolate, Solganol), and gold sodium thiomalate (Myochrysine); hydralazine (Hydra-Zide); lithium (Eskalith, Lithobid); medications to treat human immunodeficiency virus (HIV) or acquired immunodeficiency syndrome (AIDS); methicillin (Staphcillin); nitrates; penicillin and sulfa antibiotics; penicillamine (Cuprimine, Depen); primaquine; propranolol (Inderal); rifampin (Rifadin, Rimactane); tacrolimus (Prograf); vancomycin (Vancocin); or if you have ever taken the Chinese weight-loss herb aristolochia.

If you experience any of the following symptoms, call your doctor immediately: extreme tiredness, weakness, or discomfort; upset stomach; vomiting; stomach pain; decreased appetite; deep and rapid breathing or shortness of breath; dizziness; light-headedness; fast or slow heartbeat; flushing of the skin; muscle pain; or feeling cold.

Tell your doctor if you regularly drink alcohol or sometimes drink large amounts of alcohol in a short time (binge drinking). Drinking alcohol increases your risk of developing lactic acidosis or may cause a decrease in blood sugar. Ask your doctor how much alcohol is safe to drink while you are taking metformin.

Keep all appointments with your doctor and the laboratory. Your doctor will order certain tests to check your body's response to metformin. Talk to your doctor about the risk(s) of taking metformin.

Why this medication is prescribed
Metformin is used alone or with other medications, including insulin, to treat type 2 diabetes (condition in which the body does not use insulin normally and therefore cannot control the amount of sugar in the blood). Metformin helps to control the amount of glucose (sugar) in your blood. It decreases the amount of glucose you absorb from your food and the amount of glucose made by your liver. Metformin also increases your body's response to insulin, a natural substance that controls the amount of glucose in the blood. Metformin is not used to treat type 1 diabetes (condition in which the body does not produce insulin and therefore cannot control the amount of sugar in the blood).

How this medication should be used
Metformin comes as a tablet and an extended-release (long-acting) tablet to take by mouth. The regular tablet is usually taken with meals two or three times a day. The extended-release tablet is usually taken once daily with the evening meal. To help you remember to take metformin, take it around the same time(s) every day. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take metformin exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor.

Swallow metformin extended-release tablets whole; do not split, chew, or crush them.

Your doctor may start you on a low dose of metformin and gradually increase your dose not more often than once every 1-2 weeks. You will need to monitor your blood sugar carefully so your doctor will be able to tell how well metformin is working.

Metformin controls diabetes but does not cure it. Continue to take metformin even if you feel well. Do not stop taking metformin without talking to your doctor.

Other uses for this medicine
This medication may be prescribed for other uses; ask your doctor or pharmacist for more information.

Special precautions
Before taking metformin:


 * tell your doctor and pharmacist if you are allergic to metformin or any other medications.
 * tell your doctor and pharmacist what other prescription and nonprescription medications, vitamins, nutritional supplements, and herbal products you are taking. Be sure to mention the medications listed in the IMPORTANT WARNING section and any of the following: amiloride (Midamor, Moduretic); antihistamines; beta-blockers such as atenolol (Tenormin), labetalol (Normodyne), metoprolol (Lopressor, Toprol XL), nadolol (Corgard), and propranolol (Inderal); calcium channel blockers such as amlodipine (Norvasc), diltiazem (Cardizem, Dilacor, Tiazac, others), felodipine (Lexxel, Plendil), isradipine (DynaCirc), nicardipine (Cardene), nifedipine (Adalat, Procardia), nimodipine (Nimotop), nisoldipine (Sular), and verapamil (Calan, Isoptin, Verelan); cimetidine (Tagamet); digoxin (Lanoxin, Lanoxicaps); furosemide (Lasix); hormone replacement therapy; insulin or other medications for diabetes; isoniazid (INH, Nydrazid); medications for asthma and colds; medications for mental illness and nausea such as fluphenazine (Prolixin), mesoridazine (Serentil), perphenazine (Trilafon), prochlorperazine (Compazine), promethazine (Phenergan), thioridazine (Mellaril), thiothixene (Navane), trifluoperazine (Stelazine), and triflupromazine (Vesprin); medications for thyroid disease; morphine (MS Contin, Roxanol, others); nicotinic acid; oral contraceptives (birth control pills); oral steroids such as dexamethasone (Decadron, Dexone), methylprednisolone (Medrol), and prednisone (Deltasone); phenytoin (Dilantin, Phenytek); procainamide (Procanbid); quinidine (Quinidex); quinine; ranitidine (Zantac); triamterene (Dyazide, Maxzide, others); or trimethoprim (Proloprim, Trimpex). Your doctor may need to change the doses of your medications or monitor you carefully for side effects.
 * tell your doctor if you have or have ever had any medical condition, especially those mentioned in the IMPORTANT WARNING section.
 * tell your doctor if you are pregnant, plan to become pregnant, or are breast-feeding. If you become pregnant while taking metformin, call your doctor.
 * if you are using the extended release tablets, you should know that sometimes the tablet shell may appear in your stool. If this occurs, it is not harmful and will not affect the way the medication works.
 * tell your doctor if you eat less or exercise more than usual. This can affect your blood sugar. Your doctor will give you instructions if this happens.

Special dietary instructions
Be sure to follow all exercise and dietary recommendations made by your doctor or dietitian. It is important to eat a healthful diet.

What to do if you forget a dose
Take the missed dose as soon as you remember it. However, if it is almost time for the next dose, skip the missed dose and continue your regular dosing schedule. Do not take a double dose to make up for a missed one.

Minor side effects
This medication may cause changes in your blood sugar. You should know the symptoms of low and high blood sugar and what to do if you have these symptoms.

You may experience hypoglycemia (low blood sugar) while you are taking this medication. Your doctor will tell you what you should do if you develop hypoglycemia. He or she may tell you to check your blood sugar, eat or drink a food or beverage that contains sugar, such as hard candy or fruit juice, or get medical care. Follow these directions carefully if you have any of the following symptoms of hypoglycemia:


 * shakiness
 * dizziness or lightheadedness
 * sweating
 * nervousness or irritability
 * sudden changes in behavior or mood
 * headache
 * numbness or tingling around the mouth
 * weakness
 * pale skin
 * hunger
 * clumsy or jerky movements

If hypoglycemia is not treated, severe symptoms may develop. Be sure that your family, friends, and other people who spend time with you know that if you have any of the following symptoms, they should get medical treatment for you immediately.


 * confusion
 * seizures
 * loss of consciousness

Call your doctor immediately if you have any of the following symptoms of hyperglycemia (high blood sugar):


 * extreme thirst
 * frequent urination
 * extreme hunger
 * weakness
 * blurred vision

If high blood sugar is not treated, a serious, life-threatening condition called diabetic ketoacidosis could develop. Call your doctor immediately if you have any of the these symptoms:


 * dry mouth
 * upset stomach and vomiting
 * shortness of breath
 * breath that smells fruity
 * decreased consciousness

Metformin may cause side effects. Tell your doctor if any of these symptoms are severe, do not go away, go away and come back, or do not begin for some time after you begin taking metformin:


 * diarrhea
 * bloating
 * stomach pain
 * gas
 * constipation
 * unpleasant metallic taste in mouth
 * heartburn
 * headache
 * sneezing
 * cough
 * runny nose
 * flushing of the skin
 * nail changes
 * muscle pain

Severe side effects
Some side effects can be serious. The following symptoms are uncommon, but if you experience any of them or those listed in the IMPORTANT WARNING section, call your doctor immediately:


 * chest pain
 * rash

Some female laboratory animals given high doses of metformin developed non-cancerous polyps (abnormal growths of tissue) in the uterus (womb). It is not known if metformin increases the risk of polyps in humans. Talk to your doctor about the risks of taking this medication.

Metformin may cause other side effects. Call your doctor if you have any unusual problems while taking this medication.

If you experience a serious side effect, you or your doctor may send a report to the Food and Drug Administration's (FDA) MedWatch Adverse Event Reporting program online [at http://www.fda.gov/MedWatch/report.htm] or by phone [1-800-332-1088].

Storage conditions needed for this medication
Keep this medication in the container it came in, tightly closed, and out of reach of children. Store it at room temperature and away from light excess heat and moisture (not in the bathroom). Throw away any medication that is outdated or no longer needed. Talk to your pharmacist about the proper disposal of your medication.

In case of emergency/overdose
In case of overdose, call your local poison control center at 1-800-222-1222. If the victim has collapsed or is not breathing, call local emergency services at 911.

Symptoms of overdose may include:


 * extreme tiredness
 * weakness
 * discomfort
 * vomiting
 * upset stomach
 * stomach pain
 * decreased appetite
 * deep, rapid breathing
 * shortness of breath
 * dizziness
 * light-headedness
 * abnormally fast or slow heartbeat
 * flushing of the skin
 * muscle pain
 * feeling cold

Other information
Keep all appointments with your doctor and the laboratory. Your blood sugar and glycosylated hemoglobin (HbA1c) should be checked regularly to determine your response to metformin. Your doctor may order other lab tests to check your response to metformin. Your doctor will also tell you how to check your response to this medication by measuring your blood or urine sugar levels at home. Follow these instructions carefully.

You should always wear a diabetic identification bracelet to be sure you get proper treatment in an emergency.

Do not let anyone else take your medication. Ask your pharmacist any questions you have about refilling your prescription.

Brand names

 * Glucophage®
 * Glucophage ® XR
 * Fortamet®