Metformin (Biguanide)
This is a class of drugs used to treat diabetics, but has also been found effective the treatment of insulin resistance and Metabolic Syndrome X. Metformin (Glucophage) is the only biguanide available in the U.S. (approved in 1994) after nearly 40 years of use in Europe.
Metformin works by slowing the rate at which the liver releases stored glucose and the absorptions of glucose into the bloodstream. Metformin can be used alone, in combination with sufonylureas, or even with patients on large doses of insulin. When given alone, metformin rarely causes hypoglycemia. However, when given in combination with either sulfonylurea or insulin, hypoglycemia can occur and the dosages of these drugs need to be adjusted.
Metformin has been associated with weight loss in some patients. It has also been shown to improve lipid profile and blood flow in patients with peripheral vascular disease.
Because of possible GI distress, it is best to start with a lower dose of metformin and gradually increase the amount. The most commonly observed side effects include: metallic taste, flatulence,
And anorexia (decreased appetite). These side effects usually vanish after a short period of time.
The primary concern with metformin is the potential for lactic acidosis. Although lactic acidosis is rare (9 cases per 100,000 patient years of therapy), and the onset is subtle (fatigue, vomiting, fever, or unusual muscular pain), it seems to be aggravated very quickly. If you experience any of these symptoms, discontinue the medication and see your physician immediately.
Metformin should not be given to patients with kidney problems, those over 80 years of age (because of the risk of renal impairment), those with a history of liver disease, or those who are taking medicine for heart failure (such as Lasix or Digoxin). Any patients undergoing an X-ray procedure with the injection of dyes should discontinue metformin therapy the day of the procedure and should hold all doses for 48 hours.
The maximum dosage is 2550mg per day. There is a new extended release (XR) formation on the market. The XR formulation should be taken all at once every day rather than spacing out during the day as is typical of the non XR formulas.
Over-the-counter Tagamet or Cimetidine may cause a 60 percent increase in the metformin plasma concentration, causing blood glucose levels to fall below normal values. If taking Procardia, it may enhance metformin absorption (which is really not a bad side effect). Metformin can cause vitamin B12 deficiency in some patients. A B12 deficiency can cause anemia and irreversible nerve damage which could be mistaken for periphereal neuropathy in patients with diabetes. If patients on metformin develop periphereal neuropathy, it might be advisable to check for B12 deficiency.
This article was originally published in the XChanges newsletter, Kathy Karas, RPh., Volume 2 No. 5; September/October 2004
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