Metformin is a prescription medication indicated for the treatment of type 2 diabetes, either alone or combination with other drugs. It is the only medication that belongs to a class called the biguanides. Metformin works by decreasing the amount of glucose (sugar) the liver produces, and decreases the amount absorbed by the intestines. It also utilizes insulin more effectively in the body. Through these actions it lowers blood sugar. Like all medications, metformin has many potential side effects and comes with precautions or warnings.
Common Side Effects
Most of the common side effects associated with metformin have to do with the gastrointestinal system. Diarrhea occurs in up to 53 percent of individuals on the drug. About 6 to 25 percent experience nausea and vomiting, and about 6 percent have abdominal discomfort and indigestion. Other possible side effects are flatulence (about 12 percent) and metallic taste in the mouth (about 5 percent). To avoid these effects, it may help to eat small, frequent meals or chew gum, as well as to take the medication with meals.
Vitamin B-12 Deficiency
Metformin can prevent the absorption of vitamin B-12, leading to a deficiency in about 7 percent of people. The doctor usually monitors patients for B-12 and suggests supplements as necessary.
Weakness and Dizziness
Metformin can cause weakness in up to 9 percent of people. Dizziness or light-headedness may also be present, and people who notice these effects should not drive or engage in activities that require alertness.
Hypoglycemia
Metformin is working to lower the blood sugar, so it can potentially cause low blood sugar (hypoglycemia). Signs of hypoglycemia include dizziness, weakness, nervousness, shaking, hunger and sweating. People should carry hard candy to take in order to raise the blood sugar if these symptoms occur. A class of drugs called beta-blockers may mask these symptoms, so patients should make sure their doctor knows all the medications they are using.
Lactic Acidosis
One warning related to metformin is the possibility of developing lactic acidosis. Lactic acidosis is the accumulation of lactic acid in the bloodstream. It occurs when it is not removed as quickly as it builds up, and usually in the absence of oxygen. Lactic acidosis is seen in less than 1 percent of individuals and is life threatening. Metformin should be discontinued in patients with cardiovascular collapse, acute myocardial infarction (heart attack), acute congestive heart failure and respiratory failure.
Renal Impairment
Metformin is eliminated from the body through the kidneys; those with renal impairment may accumulate the drug. This increases the risk for lactic acidosis. Anyone over the age of 80 should not be administered metformin due to decreased renal function that occurs with normal aging. Any drug that is eliminated via the kidneys may lead to an increase of metformin in the body. If an individual is undergoing radiologic studies and will be administered contrast materials, metformin will need to be stopped 48 hours in advance to avoid alteration in renal function.
Impaired Liver Function
Metformin should be avoided in patients with impaired liver function. Patients with liver disease are at an increase risk of lactic acidosis. People should avoid the use of alcohol to avoid liver complications and lactic acidosis.
References
- "Drug Information Handbook, 15th Edition"; Charles F. Lacy, R.Ph., Pharm.D., et al.; 2007
- "Pharmacotherapy: A Pathophysiologic Approach"; Joseph T. Dipiro et al; 2008
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