Aug. 14 (Bloomberg) -- GlaxoSmithKline Plc's Avandia and Takeda Pharmaceutical Co.'s Actos, the world's best-selling diabetes pills, will carry U.S. regulators' strictest warning on the risk of heart failure.

The drugmakers agreed to highlight an existing caution by outlining it in a black box on prescribing information, the Food and Drug Administration said today in an e-mailed statement. London-based Glaxo said it previously committed to make the material more prominent. Heart failure is a condition in which the heart doesn't pump enough blood.

Avandia was the top diabetes pill and Glaxo's second-biggest drug last year, generating revenue of $3.3 billion worldwide. Sales fell after a study on May 21 by the Cleveland Clinic tied Avandia to a 43 percent increased risk of heart attacks. Actos generated $2.77 billion last year, making it No. 2.

``Despite the warnings and information already listed in the drug labels, these drugs are still being prescribed to patients without careful monitoring for signs of heart failure,'' said Steven Galson, director of the FDA's Center for Drug Evaluation and Research, in the statement.

Avandia and Actos belong to a class of medicines known as thiazolidinediones, or TZDs. The pills, used to treat type 2 diabetes, work by making people with the disease more sensitive to the hormone insulin. The medicines have been taken by more than 15 million patients since 1999.

246 Million Diabetics

An estimated 246 million people, almost 6 percent of the world's adult population, suffer from diabetes, and 3.8 million a year die from it, according to the International Diabetes Federation. There is an epidemic of type 2 diabetes, fueled by rising obesity rates, aging and sedentary lifestyles, public health officials said.

``This has obviously been foreshadowed for some time,'' said Chris Viehbacher, president of U.S. pharmaceuticals for GlaxoSmithKline, on a conference call discussing the FDA announcement. ``I don't see a significant impact on our prescriptions in dollar value.''

The FDA's action isn't based on any new safety data, said Robert Spanheimer, Takeda's senior director of diabetes in North America, in a telephone interview. The risk of heart failure has been part of the Actos label since the drug was approved in 1999. The new warning will feature the risk more prominently, he said.

Welcome News

The new warning on the risk of heart failure was welcomed by Steven Nissen, head of cardiology at the Cleveland Clinic and author of the May study linking Avandia to heart attacks, a different disorder.

``Step in the right direction,'' Nissen said in a telephone interview. ``Now we really need the FDA to act swiftly'' on heart attacks and related complications.

A panel of advisers to the FDA voted 22-1 on July 31 to recommend keeping Avandia on the market after reviewing Nissen's study and other evidence. Panel members said the FDA should add warnings on heart attacks to the drug's prescribing information and suggested that doctors be advised not to use Avandia for patients who take insulin or have heart disease.

Takeda doesn't expect the agency to ask for any warnings linking the risk of heart attack to Actos, Spanheimer said.

The cells of type 2 diabetes patients don't properly use insulin, a hormone that turns blood sugar into energy. Persistent high blood sugar eventually damages the nerves and blood vessels, leading to blindness, kidney failure and death.

Double the Risk

An analysis of existing research published last month in the journal Diabetes Care found that Avandia and Actos doubled the risk of heart failure in diabetics.

Treatment with Avandia and Actos may increase the likelihood by causing fluid retention or swelling, which can make the heart work harder. The study found that a quarter of heart-failure cases occur in people younger than 60.

Researchers projected that 1 in every 50 patients taking Avandia or Actos over a 26-month period would be hospitalized for heart failure.

``This warning tells us clearly that patients need to ask their doctor whether they have any symptoms of heart failure or are at risk for heart failure before taking these two drugs,'' said Larry Deeb, president of science and medicine for the American Diabetes Association, in a telephone interview today.

``As a patient, you should ask yourself, `How well is my heart pumping?' and `Do I have trouble going up stairs?' and consider alternate medicines if the answer is yes,'' Deeb said.

To contact the reporter on this story: Emily Brown in Washington at ebrown18@bloomberg.net.

Last Updated: August 14, 2007 18:56 EDT