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Diabetes Drug Reduces Deaths, But Doctors Aren’t Sure How

Diabetes screening

A man's finger is pricked to test cholesterol and blood sugar on August 13, 2009, in Newark, New Jersey. Rick Gershon / Getty Images

A diabetes pill has been shown, for the first time, to reduce deaths among patients taking it. It's a big finding — and Lilly, the drug company that makes it, is trumpeting the results.

The drug, called Jardiance, lowered heart disease deaths by 38 percent and deaths from any cause by 32 percent over three years, an international group of researchers reported in The New England Journal of Medicine.

But doctors are not sure how the drug is doing it.

"I think this is a wow. I can't think of very many times that we've seen a reasonably large clinical trial where we have found a one-third reduction in death," said cardiologist Dr. Steve Nissen of the Cleveland Clinic, who reviewed the results but who was not involved in the trial.

There are many different classes of diabetes drugs, and they're designed to lower levels of sugar in the blood. The U.S. Food and Drug Administration approves them based on how well they do this.

The hope is the drugs will reduce all the deadly and crippling effects of diabetes, which damages tiny blood vessels as the sugar builds up in blood. It can cause blindness, force the amputations of limbs and, worst of all, it damages the heart.

"Cardiovascular disease is far and away the leading cause of death in diabetes, affecting 60-70 percent of all diabetics," Nissen said.

Type-2 diabetes is a different condition from the much rarer type-1 diabetes, which is an autoimmune disease in which the body mistakenly attacks insulin-producing cells. Type-2 diabetes is linked with poor diet, too little exercise and, sometimes, genetics.

Jardiance lowers blood sugar but the company also wanted to be able to show it reduced the rate of heart disease and deaths.

Study: Many diabetics are unaware they have disease 0:20

The researchers tested it on more than 7,000 patients in 42 countries who already had both diabetes and heart disease and had a high risk of heart attack, stroke and heart failure. They got one of two doses of Jardiance or a placebo.

The drug did not reduce rates of heart attack or stroke. But it did lower rates of heart deaths: 3.7 percent of the patients who got Jardiance died of heart disease, compared to 5.9 percent of those given placebo.

Just under 6 percent of the patients taking Jardiance died from any cause over the average of three years they were followed, compared to 8.3 percent of those taking placebo. And 2.7 percent of the Jardiance patients were hospitalized for heart failure, compared to 4.1 percent of patients taking placebo.

"It is the first that we've seen unequivocal evidence of this kind of benefit for a diabetes drug," Nissen told NBC News.

Dr. David Nathan, who directs the diabetes center at Massachusetts General Hospital, agreed. But he said the drug is not likely to be suitable for all diabetes patients.

"The reason this is important is because it is the first one to show potential benefit, a pretty big one, a pretty powerful effect," Nathan told NBC News.

"But in order for the company to do this study, they picked patients at very high cardiovascular risk, many of whom already had heart attacks or strokes, in order for them to accrue enough events over a short period of time so they could complete the study quickly. Of course, the company will use these data to recommend the drug for everyone, when in fact the benefit was true in a particularly ill population."

Jardiance is a sodium-glucose cotransporter-2 (SGLT2) inhibitor. It lowers blood sugar by causing the kidneys to shift it into the urine.

It could be this mechanism is lowering blood pressure, said Nissen.

"The drug causes the kidney to spill glucose sugar into urine, along with volume, so it acts as a diuretic, with a favorable effect on blood pressure," he said.

"Often with drugs, we don't fully understand the mechanism of action," he added. The drug also caused some weight loss, and other studies have shown even a little weight loss can have big health benefits.

"I wish things could have been clearer, but boy that was a big effect on death," Nissen added.

Other drugs in the same class include Invokana, Farxiga and Glyxambi. In May, the FDA warned that drugs in this class could cause ketoacidosis, a dangerous condition caused by high levels of acids in the blood called ketones.

There's a big market for such drugs. Half of all Americans have diabetes or blood sugar so high it puts them on the borderline.

Diabetes directly kills more than 71,000 people a year, according to the American Diabetes Association.

A month's supply of Jardiance, which is known generically as empagliflozin, costs between $350 and $400, according to the website GoodRx.

Doctors recommend trying diet and exercise first to reduce the risk of type-2 diabetes. There are eight classes of pills on the market to help control diabetes,

For harder-to-treat cases, there are three injectable drugs, and people with diabetes may have to use insulin injections as a last resort.