CHICAGO – A sizable number of diabetic patients with kidney disease or heart failure are inappropriately prescribed a common drug that could potentially kill them, a new study suggests.

Nearly one-fourth of patients whose prescriptions for the drug metformin were studied had at least one of those conditions despite labeled warnings against use in such patients.

Metformin, sold as Glucophage, can cause a rare side effect called lactic acidosis, a buildup of lactic acid in the blood that is fatal in about 50 percent of cases. Patients with heart disease or kidney failure are especially prone.

The drug package insert contains a black-box warning – required by the government for drugs with potentially serious side effects – and says it should not be used by patients with kidney disease or on drug treatment for heart failure.

While none of the 100 patients studied had developed lactic acidosis, the study “may underestimate the frequency of contraindications and it is difficult to determine whether clinicians are aware they are prescribing metformin against a black-box warning,” the researchers said.

Lead researcher Cheryl Horlen said the problem isn’t unique to the University of North Carolina-Chapel Hill hospital pharmacy where the study was done. University of Pittsburgh researchers and recent European studies found similar rates of inappropriate use.

More than 25 million prescriptions were written for metformin in 2000, according to the researchers.

Metformin helps the body use insulin and control blood sugar levels, and Horlen said patients shouldn’t stop taking the drug without consulting their doctors.

The study is one of several on diabetes published in Wednesday’s Journal of the American Medical Association. It’s the first JAMA issue devoted entirely to research on diabetes, which has reached epidemic levels and afflicts about 17 million people nationwide.

“I can’t imagine anybody in the United States who doesn’t have someone in their family or some close friend with diabetes,” JAMA editor Dr. Catherine DeAngelis said.

Diabetes impairs the body’s ability to produce or make proper use of insulin, resulting in elevated blood sugar levels that can damage the kidneys, heart, eyes and other organs.

Glucophage is among the most common drugs for Type II diabetes, which is linked to obesity and is sometimes called adult-onset, although it has started showing up in children.

Bonnie Jacobs, a spokeswoman for Glucophage maker Bristol-Myers Squibb Co., said the warnings “are clearly outlined” on the label.

Recent research from Harvard Medical School and Public Citizen Health Research Group suggested doctors don’t pay close enough attention to drug warning labels, a problem also raised by the Food and Drug Administration.

Dr. Malcolm Taylor, president of the Association of Black Cardiologists, said patients’ lack of knowledge about diabetes drugs might be partly to blame.

His group and the American Association of Diabetes Educators are launching a nationwide education campaign this week, including a new Web site to raise awareness about the link between diabetes and heart disease, the leading cause of diabetes-related death.

In other JAMA research, a Kaiser Permanente study suggests that giving blacks and whites similar health care access can help ease racial disparities in rates of complications such as severe kidney disease, which affects blacks disproportionately.

However, the study of 62,432 patients enrolled in a northern California Kaiser insurance plan found some differences persisted despite equal access, suggesting genetic differences may help explain the racial disparities, Kaiser scientist Andrew Karter said.

In a JAMA editorial, Dr. Christopher Saudek, president of the American Diabetes Association, said the studies underscore the need for insurers and policy-makers to adequately address chronic diseases like diabetes, which require a lifetime of treatment.

“We should be paying to keep people out of the hospital, to keep them as pain-free as possible and as free from complications,” Saudek said.