Generic Name:  metformin

Brand Names: Fortamet, Glumetza, Riomet

Metformin is an oral diabetes medicine that helps control blood sugar levels. Metformin is used together with diet and exercise to improve blood sugar control in adults with type 2 diabetes mellitus.

Metformin does not help patients who have insulin-dependent or type 1 diabetes because they cannot produce their own insulin.

Glucophage (metformin) is an anti-diabetic medication used to treat type 2 diabetes. It works by decreasing the amount of sugar that your liver produces and your intestines absorb. Glucophage can help you lose weight by reducing your appetite. It may also help you to keep from gaining back the weight you have lost. Glucophage is usually taken with meals. You may take it up to 3 times a day with meals. Follow the directions on your prescription label carefully, and ask your doctor or pharmacist to explain any part you do not understand. Take Glucophage exactly as directed. Do not take more or less of it or take it more often than prescribed by your doctor. Your doctor may gradually increase your dose to find the best dose for you.

If you take Glucophage with insulin or other diabetes medications, your blood sugar could get too low. Low blood sugar (hypoglycemia) can happen to everyone who has diabetes. Symptoms include headache, hunger, sweating, confusion, irritability, dizziness, or feeling shaky. Always keep a source of sugar available in case you have low blood sugar. Sugar sources include orange juice, glucose gel, candy, or milk. If you have severe hypoglycemia and cannot eat or drink, use an injection of glucagon. Your doctor can give you a prescription for a glucagon emergency injection kit and tell you how to give the injection.

Pharmacokinetics

Metformin is rapidly absorbed from the gastrointestinal tract and maximum plasma concentrations occur 1-2 hours after oral administration. The extent of absorption (AUC) increases in proportion to the dose administered, but there is considerable interindividual variability in the rate of absorption.

Bioavailability is not decreased by food. Metformin is excreted unchanged in the urine and does not undergo hepatic metabolism (no cytochrome P450 involvement). Renal clearance (CLr) of metformin is directly proportional to creatinine clearance (CLcr). Therefore, CLcr decreases and metformin half-life increases with declining renal function. In patients with normal renal function, there are no differences between single- and multiple-dose pharmacokinetics.

Special Populations

Elderly:  In elderly subjects with normal renal function, there are no differences between single- and multiple-dose pharmacokinetics.

Renal Impairment:  The half-life of metformin is prolonged and the AUC is increased in proportion to the degree of renal impairment. creatinine clearance less than 60 mL/min). No dosage adjustment is required in patients with mild to moderate renal impairment (CLcr= 60–90 mL/min). Metformin should be discontinued at the time of or before an imaging procedure using iodinated contrast materials, as use of these products may result in acute alteration of renal function. Dialysis does not alter serum concentrations of metformin.

Hepatic Impairment:  The pharmacokinetics of metformin is not altered in patients with hepatic impairment. No dosage adjustment is required in patients with mild to moderate hepatic impairment. Metformin should be used with caution in patients with severe liver impairment; serum concentrations of metformin may be increased, increasing the risk for lactic acidosis. Metformin should be discontinued at the time of or before an imaging procedure using iodinated contrast materials, as use of these products may result in acute alteration of renal function.

Drug interactions

Metformin is primarily eliminated by the kidney and doses should be adjusted based on renal function.

There are no significant interactions between metformin and other commonly used medications such as acarbose, ranitidine, furosemide, nifedipine, or glipizide.

Metformin may increase the plasma concentrations of statins (HMG-CoA reductase inhibitors). The clinical significance of this interaction is unknown; however, caution is advised when prescribing these medications together.

The concomitant use of metformin and cationic drugs that are eliminated by tubular secretion (e.g., cimetidine) may result in increased plasma concentrations of metformin.

Caution is advised when metformin is used in combination with cationic medications that are eliminated by tubular secretion (e.g., ranitidine, cimetidine, quinine, procainamide, and trimethoprim).

Metformin may increase the plasma concentrations of oral contraceptives. The clinical significance of this interaction is unknown; however, caution is advised when prescribing these medications together.

Side Effects

The most common side effects of metformin are gastrointestinal in nature and include diarrhea, flatulence, indigestion, nausea, and vomiting. These side effects usually occur at the beginning of treatment and resolve with continued therapy.

Other less common side effects include dizziness, headache, skin rash, and weakness.

Lactic acidosis is a rare but serious side effect that may occur with the use of metformin. Lactic acidosis is a medical emergency that must be treated in the hospital. Symptoms of lactic acidosis include abdominal pain, muscle pain, shortness of breath, irregular heartbeat, and feeling cold. If you experience any of these symptoms while taking metformin, call your doctor immediately.

Dosage and Administration

The recommended starting dose of metformin is 500 mg twice daily, given with meals. The dose may be titrated upward to a maximum of 2,000 mg per day, given in divided doses.

If you miss a dose of metformin, take the missed dose as soon as you remember it. If it is almost time for your next dose, skip the missed dose and continue with your regular dosing schedule. Do not take a double dose to make up for a missed one.

Overdose

Symptoms of metformin overdose include hypoglycemia, lactic acidosis, and gastrointestinal upset.

If you think you have overdosed on metformin, call your doctor or poison control center immediately.

Storage

Metformin should be stored at room temperature, 15-30°C (59-86°F). Keep this medication in a tightly closed container. Protect from light and moisture. Do not store in the bathroom. Keep all medications away from children and pets. Do not flush medications down the toilet or pour them into a drain unless instructed to do so. Properly discard this product when it is expired or no longer needed. Consult your pharmacist or local waste disposal company for more details about how to safely discard your product.