Metformin, or Glucophage, is a drug commonly used to treat type 2 diabetes mellitus. It is available in both short and long-acting forms. RxList reports the most common side effects associated with metformin, occurring in more than 5 percent of patients using the drug, are diarrhea, nausea, vomiting, flatulence, diffuse lack of strength, headache, indigestion and abdominal discomfort. Metformin-induced renal side effects are rare but can be lethal.
Metformin reduces the overproduction of glucose by the liver, which is what frequently causes high morning blood glucose. In fact, metformin is often first prescribed because of high morning blood glucose, and research bears out its effectiveness at alleviating this common problem. Long-term research studies (those lasting five years or longer) have also shown metformin to reduce damage to the small blood vessels, a common consequence of chronic high blood glucose. Conditions that can result from this damage include neuropathy, retinopathy, and nephropathy.
Effects of metformin on kidneys
Metformin carries a low risk of lactic acidosis, a very serious side effect. Lactic acid is a chemical made by muscle cells; the kidneys must get rid of lactic acid, otherwise it builds up in the blood. When too much lactic acid accumulates in the blood, a person develops lactic acidosis. The symptoms are not very specific: abnormal breathing, nausea and vomiting, abdominal pain, and confusion are all common. The condition is very treatable if it is detected early but may lead to organ damage or even death if not corrected. Metformin increases lactic acid production. If the kidneys are working properly, this isn't a problem. However, in people who have kidney disease, usually with an elevated creatinine level, metformin increases the risk of lactic acidosis, so the drug should not be used.
In other situations where the kidney function may be reduced, such as in people who have heart failure or are on diuretics, a doctor may recommend against using metformin. The intravenous dye given for CT scans and certain other X-ray tests may damage the kidneys, so the usual recommendation is to stop metformin for about twenty-four to forty-eight hours around the time of the test, until it's clear that the kidneys weren't harmed. Some doctors are hesitant to use metformin in older people -- usually those over 80 -- because they often have some underlying kidney dysfunction and are prone to dehydration; both are conditions that can make kidney function even worse if they become ill.
Metformin is contraindicated in any condition that may increase the risk of lactic acidosis, including heart failure, kidney disorders (creatinine levels over 150 μmol/l,although this is an arbitrary limit), lung disease and liver disease. It is recommended that metformin be temporarily discontinued before any radiographic procedure involving iodinated contrast (such as a CT scan or angiogram) as contrast may temporarily impair kidney function and indirectly lead to lactic acidosis.