Medications » Metformin

Drug: Metformin


Medication disclaimers


BLACK BOX WARNING: METFORMIN MAY CAUSE LACTIC ACIDOSIS

Postmarketing cases of metformin-associated lactic acidosis have resulted in death, hypothermia, hypotension, and resistant bradyarrhythmias. Symptoms included malaise, myalgias, respiratory distress, somnolence, dizziness, changes in heart rate/rhythm, and abdominal pain. Laboratory abnormalities included elevated blood lactate levels, anion gap acidosis, increased lactate/pyruvate ratio; and metformin plasma levels generally >5 mcg/mL. In more than 20,000 patient-years exposure to metformin in clinical trials, there were no reports of lactic acidosis. Reported cases have occurred primarily in diabetic patients with significant renal insufficiency, including both intrinsic renal disease and renal hypoperfusion, often in the setting of multiple concomitant medical/surgical problems and multiple concomitant medications.

Risk factors include renal impairment, concomitant use of certain drugs, age ≥65 years old, radiological studies with contrast, surgery and other procedures, hypoxic states, excessive alcohol intake, and hepatic impairment. Lactic acidosis is a medical emergency and requires immediate treatment in the hospital.

WARNING

Before using metformin, tell your health care provider about your medical history, especially if you have:

  • kidney disease
  • heart disease or congestive heart failure
  • liver disease
  • metabolic acidosis or diabetic ketoacidosis
  • high ketone levels in your blood or urine
  • you use insulin or other diabetes medications

Talk to your health care provider if you are planning to become pregnant or if pregnant or breastfeeding. Avoid alcohol while taking this medication. Talk to your health care provider about discontinuing metformin prior to a surgical procedure or an iodinated contrast imaging procedure. Stop metformin and notify your health care provider immediately if you have an illness with severe diarrhea and/or vomiting resulting in dehydration.

SIDE EFFECTS

Many people experience no side effects while taking metformin. The most common side effects of metformin include:

  • diarrhea
  • nausea/vomiting
  • upset stomach (gas, bloating, and stomach cramps)

These symptoms may subside after the body adjusts to the medication. Taking your medicine with the evening meal can help reduce these side effects.

Additional but rare side effects include:

  • low blood sugar (hypoglycemia)
  • feeling cold
  • unusual muscle pain
  • dizziness
  • slow or irregular heart rate
  • trouble breathing
  • metallic taste
  • changes to nails on fingers and toes
  • Low b12 levels

DRUG INTERACTIONS

As with other medications, metformin can interact with alcohol and certain medications, including angiotensin-converting enzyme (ACE) inhibitors, beta-blockers, corticosteroids, hormone replacement therapy and estrogens, oral contraceptives, carbonic anhydrase inhibitors, nifedipine, thiazides or furosemide and other diuretics, phenothiazines, phenytoin, nicotinic acid (niacin), multidrug and toxin extrusion inhibitors, sympathomimetics, calcium channel blockers, isoniazid (antibiotic for tuberculosis), insulin and glyburide or other medications for diabetes, and medications for thyroid disease.

Please consult the pharmaceutical packaging for a full list of side effects, warnings, interactions and additional information.

To report suspected adverse reactions to metformin contact the FDA at 1-800-FDA-1088 or www.fda.gov/medwatch.

In case of emergencies, please call 911 or go to the nearest emergency room.