Metformin

Metformin is a drug approved by the U.S. Food and Drug Administration as a prescription medication to treat diabetes. This medication is used to decrease hepatic (liver) glucose production, decrease GI glucose absorption and increase target cell insulin sensitivity. This medication is a treatment indicated as an adjunct to diet, exercise, and lifestyle changes such as weight loss to improve glycemic (blood sugar) control in adults with type 2 diabetes. Many patients with type 2 diabetes will eventually need to take insulin by injection. Metformin does not cause weight gain.

About Type 2 Diabetes

Type 2 diabetes (also known as adult-onset or non-insulin-dependent diabetes) is the most common form of diabetes. Type 2 diabetes is a condition in which the body does not process insulin properly, resulting in elevated blood sugar (blood glucose). Insulin is a hormone that is produced in the pancreas. Type 2 diabetes is diagnosed more often in people who are overweight or obese, and who are not physically active. Patients with diabetes should also note that a healthy weight improves cholesterol levels and overall health. Insulin resistance is a condition that is commonly seen in type 2 diabetes, where it becomes difficult for the body to use the insulin that is produced. Certain genes that affect insulin production rather than insulin resistance are risk factors for developing type 2 diabetes. Family history of diabetes is a risk factor, and people of certain races or ethnicities are at higher risk. Abnormal glucose production by the liver can also lead to elevated blood sugar (glucose) levels.

Metformin is available under the following different brand names: Glucophage, Glucophage XR, Fortamet, Glumetza, and Riomet.

Dosages of Metformin Should Be Given As Follows:

Adult Dosage Forms & Strengths for Diabetes

• Tablet, immediate-release
  • 500 mg
  • 850 mg
  • 1000 mg
• Extended-release tablet
  • 500 mg
  • 750 mg
  • 1000 mg
  • Oral solution
  • 500 mg
  • 750 mg
  • 1000 mg

Pediatric Dosage Forms & Strengths for Diabetes

• Tablet, immediate-release
  • 500 mg
  • 850 mg
  • 1000 mg
• Extended-release Tablet
  • 500 mg
  • 750 mg
  • 1000 mg
• Oral solution
  • 500 mg
  • 750 mg
  • 100 mg

Dosage Considerations

For Adults With Type 2 Diabetes Mellitus

• Monotherapy or with sulfonylurea
• Immediate-release tablet or solution
  • Initial dose: 500 mg orally every 12 hours or 850 mg orally once/day with meals; increase every two weeks
  • Maintenance doses: 1500-2550 mg/day taken orally divided once every 8-12hr with meal
  • Not to exceed 2550 mg/day
• Extended-release
  • Glucophage XR: 500 mg orally once/day with dinner; titrate by 500 mg/day each week; not to exceed 2000 mg/day
  • Fortamet: 500-1000 mg orally once/day; titrate by 500 mg/day each week; not to exceed 2500 mg/day
  • Glumetza: 1000 mg orally once/day; titrate by 500 mg/day each week; not to exceed 2000 mg/day

For Prevention of Type 2 Diabetes

• 850 mg by mouth every day
• Target dosing: 850 mg orally every 12 hours
• Dosage Modifications
• Hepatic (liver) impairment: Avoid use; risk of lactic acidosis.
• Renal (kidney) impairment
• Obtain eGFR before starting metformin
• eGFR less than 30 mL/min/1.73 m²: Contraindicated
• eGFR 30-45 mL/min/1.73 m²: Not recommended to initiate treatment
• Monitor eGFR at least annually or more often for those at risk for renal impairment (e.g., elderly)
• If eGFR falls below 45mL/min/1.73 m² while taking metformin, health risks and benefits of continuing therapy should be evaluated
• If eGFR falls below 30 mL/min/1.73 m²: while taking metformin, discontinue the drug
• Polycystic Ovary Syndrome (Orphan)
• Orphan designation for the treatment of pediatric polycystic ovary syndrome

Pediatric Dosage Considerations

Type 2 Diabetes Mellitus

Immediate-release (10-16 years)

• Initial: 500 mg orally every 12 hours
• Maintenance: Titrate once/week by 500 mg; no more than 2000 mg/day in divided doses

Immediate-release (17 years of age and older)

• Initial dose: 500 mg orally every 12 hours or 850 mg orally once/daily with meals; increase every two weeks
• Maintenance doses: 1500-2550 mg/day orally divided once every 8-12hr with meal
• No more than 2550 mg/day

• Safety and efficacy not established

• Glucophage XR: 500 mg orally once/daily with dinner; titrate by 500 mg/day once each week; not to exceed 2000 mg/day
• Fortamet: 500-1000 mg orally once/daily; titrate by 500 mg/day once each week; not to exceed 2500 mg/day

Dosage Modifications of Medication

Renal impairment (Poor kidney function)

• Obtain eGFR before initiating metformin
• eGFR less than 30 mL/min/1.73 m²: Contraindicated
• eGFR 30-45 mL/min/1.73 m²: Initiating not recommended
• Obtain GFR at least annually in all patients taking metformin; assess eGFR more frequently in patients at increased risk for renal impairment (e.g., elderly)
• If eGFR falls to less than 45 mL/min/1.73 m² during treatment: Assess the benefits and risks of continuing treatment
• If eGFR falls to less than 30 mL/min/1.73 m² during treatment: Discontinue

Geriatric Dosage

Elderly patients with diabetes are more likely to have decreased renal function with the use of this drug; contraindicated in patients with renal impairment, carefully monitor renal function in the elderly and use with caution as age increases.

Not for use in patients over 80 years unless normal renal function established initial and maintenance dosing of metformin should be conservative in patients with advanced age due to the potential for decreased renal function in this population.

Controlled clinical studies of this drug did not include sufficient numbers of elderly patients with diabetes to determine whether they respond differently from younger patients with diabetes.

Side effects of metformin include:

• physical weakness (asthenia)
• diarrhea
• gas (flatulence)
• symptoms of weakness, muscle pain (myalgia)
• upper respiratory tract infection
• low blood sugar (hypoglycemia)
• abdominal pain (GI complaints), lactic acidosis (rare)
• low blood levels of vitamin B-12
• nausea
• vomiting
• chest discomfort
• chills, dizziness
• bloating/abdominal distention
• constipation
• heartburn

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.

If your doctor has directed you to use this medication for diabetes, your doctor or pharmacist may already be aware of any possible drug interactions and may be monitoring you for them. Do not start, stop, or change the dosage of any medicine before checking with your doctor, health care provider, or pharmacist first.

Severe Interactions of Metformin include:

There are no severe interactions from the use of metformin.

Serious Interactions of Metformin include:

• Contrast media (iodinated)
• Ethanol
• Ioversol

Drug Interactions with Metformin are:

• Metformin has moderate interactions with at least 74 different drugs.
• Metformin has mild interactions with at least 87 different drugs.

This document does not contain all possible interactions. Therefore, before using this product, tell your doctor or pharmacist of all the products you use. Keep a list of all your medications with you, and share the list with your doctor and pharmacist. Check with your physician if you have health questions or concerns.

Warnings

Metformin has moderate interactions with at least 74 different drugs.

Keep out of reach of children. In case of overdose, get medical help or contact a Poison Control Center immediately.

Contraindications

Contraindication includes hypersensitivity, chronic heart failure, metabolic acidosis with or without coma, diabetic ketoacidosis (DKA), severe renal disease, abnormal creatinine clearance resulting from shock, septicemia, or myocardial infarction and lactation.

Effects of Drug Abuse

There are no effects of drug abuse from the use of metformin.

Short-Term Effects

There are no short-term effects from the use of metformin.

Long-Term Effects

There are no long-term effects from the use of metformin.

Cautions

Use with caution in patients with congestive heart failure, fever, trauma, surgery, the elderly, renal impairment, or hepatic impairment.

Instruct patients to avoid heavy alcohol use.

Suspend therapy prior to any type of surgery.

Rare, but serious, lactic acidosis can occur due to accumulation.

Possible increased risk of cardiovascular (CV) mortality.

May cause ovulation in anovulatory and premenopausal polycystic ovary syndrome (PCOS) patients.

It may be necessary to discontinue therapy with metformin and administer insulin if patient is exposed to stress (fever, trauma, or infection).

Ethanol may potentiate metformin's effect on lactate metabolism.

May impair vitamin B12 or calcium intake/absorption; monitor B12 serum concentrations periodically with long-term therapy.

Not indicated for use in patients with type 1 diabetes mellitus that are insulin dependent due to lack of efficacy.

Withhold in patients with dehydration and/or prerenal azotemia.

Iodinated contrast imaging procedures.

Discontinue metformin at the time of or before an iodinated contrast imaging procedure in patients with an eGFR between 30-60 mL/minute/1.73 m²; in patients with a history of liver disease, alcoholism, or heart failure; or in patients who will be administered intra-arterial iodinate contrast.

Reevaluate eGFR 48 hr after the imaging procedure; restart metformin if renal function is stable.

Pregnancy and Lactation

Use in pregnancy may be acceptable. Either animal studies show no risk but human studies not available or animal studies showed minor risks and human studies done and showed no risk.

Not recommended when lactating as metformin enters breast milk.