Chicago ? Americans with diabetes nearly doubled their spending on drugs for the disease in just six years, with the bill last year climbing to an eye-popping $12.5 billion.

Newer, more costly drugs are driving the increase, said researchers, despite a lack of strong evidence for the new drugs’ greater benefits and safety. And there are more people being treated for diabetes.

The new study follows updated treatment advice for Type 2 diabetes, issued last week. In those recommendations, an expert panel told doctors to use older, cheaper drugs first.

And a second study, also out Monday, adds to evidence that metformin – an inexpensive generic used reliably for decades – may prevent deaths from heart disease while the newer, more expensive Avandia didn’t show that benefit.

“We need to pay attention to this,” said Dr. David Nathan, diabetes chief at Boston’s Massachusetts General Hospital, who wrote an editorial but wasn’t involved in the new studies. “If you can achieve the same glucose control at lower cost and lower side effects, that’s what you want to do.”

The studies, appearing in Monday’s Archives of Internal Medicine, were both funded by federal grants.

In one, researchers from University of Chicago and Stanford University looked at which pills and insulin doctors prescribed and total medication costs. Diabetes drug spending rose from $6.7 billion in 2001 to $12.5 billion in 2007, a period when costs dropped for metformin.

More patients got multiple prescriptions as new classes of drugs came on the market. And more patients with diabetes were seeing doctors, increasing from 14 million patients in 2000 to 19 million in 2007.

“There’s been a remarkable change in diabetes treatments and remarkable increases in the cost of treatments over the past several years,” said study co-author Dr. Caleb Alexander, assistant professor of medicine at the University of Chicago.