Folio News Story
January 20, 2006

Study confirms fatal risks of common diabetes drug

Researchers find metformin safer than sulfonylurea drugs

by Geoff McMaster
Folio Staff

A drug used by more than a quarter of Canadians with Type 2 diabetes does more harm than good, with potentially deadly effects on the heart, according to a study authored by a group of U of A researchers.

Dr. Jeffrey Johnson and his co-authors, all with the U of A Institute of Health Economics, discovered that risk of death from heart attacks and other causes increases with the amount of sulfonylurea drugs taken – called chlorpropamide, tolbutamide or glyburide – which have been a mainstay of diabetes treatment for some 40 years. Close to half a million Canadians are prescribed this class of drug.

The findings appear in the current edition of the Canadian Medical Association Journal.

Examining the health records of 6,000 diabetics in Saskatchewan between 1991 and 1999, Johnson and his team compared the use of sulfonylureas to the generic metformin, a less expensive treatment used by about 50 per cent of Type 2 diabetics. The results show that metformin is clearly the healthier choice.

"It's been debated for 40 years, so this research is really just adding to that debate," said Johnson. "We compared the types of drugs and their effect on mortality. The way we had been looking at them, we couldn't tell whether a drug like metformin...was really good, or the sulfonylureas were really bad."

The result, he says, is "a mix of both messages," but the most dramatic finding was that "the more you get of the sulfonylureas, the worse your outcomes." The study found that those taking doses as prescribed, or higher, were more likely to die than those who took less.

However Johnson does not recommend that patients on sulfonylureas stop taking the medication, only that they seek advice from a physician on their best option.

"And we think that for newly treated patients the first choice should be metformin," he said, adding that sulfonylureas should only be used as a third-line option.

"Type 2 diabetes gets worse over time, so as additional therapy is needed, it might be such that you need to choose these second or third-line therapies as add-on."

Johnson partly attributes the prevalence of sulfonylureas prescriptions to the fact that "old habits are hard to break," but also to the realities of drug marketing. "An old inexpensive drug that's generic, like metformin, doesn't have a marketing force behind it, and so its benefits are not proclaimed and marketed to prescribers as opposed to newer drugs that have patent protection," he said.

Metformin use has been increasing over the past five years, he says, "but we still see 25 to 30 per cent on older sulfonylureas drugs." He said he hopes the study will influence doctors' prescribing habits.

"Our contribution with this paper is an emphasis on the message that's already out there. We hope it helps to move people toward making better choices."

Incidence of Type 2 diabetes is sharply on the rise in Canada and much of the world, increasing at the same rate as obesity. It is caused by an intersection of genetic and environmental factors such as a "toxic lifestyle" involving unhealthy eating and inactivity, said Johnson.