Metformin: Safer for Heart Than Older Diabetes Drugs?

Study Suggests Diabetes Patients Taking Sulfonylureas Have Higher Risk of Heart Problems

By Charlene Laino
WebMD Health News

Reviewed by Laura J. Martin, MD

June 28, 2011 (San Diego) -- Older people with type 2 diabetes who take an older class of oral diabetes drugs called sulfonylureas may have a higher risk of developing heart problems than those who take metformin.

In a two-year study of 8,502 people with type 2 diabetes aged 65 and older, 12.4% of those who started therapy with a sulfonylurea drug had a heart attack or other heart problem, compared with 10.4% of those who started with metformin.

Additionally, people taking sulfonylurea drugs experienced heart problems sooner after starting treatment than those taking metformin.

"The findings are important because older patients with diabetes are at particular risk for cardiovascular disease, and sulfonylureas continue to remain a commonly used medication in this population," says researcher Alex Z. Fu, PhD, an associate faculty member in the department of quantitative health sciences at the Cleveland Clinic.

Sulfonylurea drugs, which include chlorpropamide, glyburide, glipizide, tolazamide, and tolbutamide, are often one of the first medications prescribed to lower blood sugar levels in people with type 2 diabetes, he says.

The findings were presented here at the 71st Scientific Sessions of the American Diabetes Association.

Metformin vs. Sulfonylureas

Nearly 26 million Americans have diabetes; 95% of them have type 2 diabetes. It develops when the body does not produce enough insulin and/or the insulin that is produced isn't used properly.

As a result, insulin can't do its job regulating blood sugar. Persistently high blood sugar levels can lead to complications ranging from blindness to kidney failure. Heart attacks and heart failure are among the major killers associated with diabetes.

Over the past two decades, many drugs have been approved to treat diabetes. The drugs improve blood sugar control, but there have also been concerns that some may raise the risk of cardiovascular events, especially in people who are already at high risk.

In 2007, Avandia was tied to heart risks, and the FDA recently announced that after Nov. 18 doctors will have to enroll patients in a special registry in order to receive the drug.

Metformin, which has been on the market since 1995, is usually recommended as a first-line treatment for diabetes because it is relatively safe and cheap, says David M. Kendall, MD, chief scientific and medical officer for the American Diabetes Association.

The sulfonylureas are also available in generic form, so they too are inexpensive.

Sulfonylureas and metformin lower blood sugar in different ways, Kendall says. Metformin suppresses excess production of sugar by the liver, while sulfonylureas promote the body's production of insulin, he says.

Studies have linked sulfonylureas to episodes of low blood sugar, or hypoglycemia, as well as weight gain, Kendall says. Additionally, other studies have linked them to heart problems.

"The cardiovascular safety of the sulfonylureas warrants continued study," Kendall tells WebMD.

For the study, the researchers examined the potential association between treatment with a sulfonylurea or metformin and subsequent heart problems in older type 2 patients using data from electronic medical records.

Fu cautions that patients were not randomly assigned to the drugs and that the study does not prove cause and effect. Also, the analysis did not take into account whether people stopped taking their drug or if they started taking medications for high blood pressure or high cholesterol, he says.

"If you have concerns about your medication, ask your doctor," Kendall says. Never stop taking the drug on your own, he says.

These findings were presented at a medical conference. They should be considered preliminary as they have not yet undergone the "peer review" process, in which outside experts scrutinize the data prior to publication in a medical journal.

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SOURCES: 71st Scientific Sessions of American Diabetes Association, San Diego, June 24-28, 2011.Alex Z. Fu, PhD, associate faculty member, department of quantitative health sciences, Cleveland Clinic.David M. Kendall, MD, chief scientific and medical officer, American Diabetes Association. ©2011 WebMD, LLC. All Rights Reserved.

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