The largest study ever done solely on blacks with heart failure raises the controversial prospect of the first drug that might be marketed to a specific racial group.

The experimental drug, BiDil (search), dramatically improved survival and cut hospitalizations for heart failure, a problem that affects 5 million Americans, blacks 2 1/2 times more often than whites.

Its maker, NitroMed, plans to seek federal approval for the two-drug combination pill by year's end.

"It's a delight to see a trial that clearly shows a benefit of therapy in a particular racial group," said Dr. Augustus Grant, past president of the Association of Black Cardiologists (search), which supported the study.

However, some specialists believe the pill also would help whites and say it should have been tested among them but wasn't for business reasons.

The study's results were reported Monday at an American Heart Association (search) meeting in New Orleans, and will be published Thursday in the New England Journal of Medicine.

Heart failure occurs when the heart is too weak to pump effectively, causing fluid to back up in the lungs — leaving people weak and short of breath. Half die within five years of diagnosis.

Earlier research suggested that standard heart failure drugs — called ACE inhibitors — do not work as well in blacks, and that blacks may have lower amounts of nitric oxide, which plays many roles in heart health, in their blood.

Two chemicals — isosorbide dinitrate and hydralazine — boost this substance, but administering the right dose is complicated when prescribed separately.

The Massachusetts biotechnology company, NitroMed, developed a combination pill that gets around this problem, but the federal Food and Drug Administration refused to license BiDil as a new drug because earlier studies involving mostly white patients showed no benefit.

There were promising signs that the medication helped the few blacks in the studies, and NitroMed won a patent to use it just among that minority group.

The company then launched a study of 1,050 blacks. Half of them got standard heart failure drugs and a placebo; the other half got standard drugs plus BiDil. The study was stopped ahead of schedule last year when doctors saw BiDil clearly was better.

After roughly two years' use, only 6.2 percent of the patients who took BiDil had died versus 10.2 percent who got only standard heart failure drugs. That translates to a 43 percent reduction in deaths, said Dr. Anne Taylor of the University of Minnesota, one of the study's leaders.

Only 16.4 percent on BiDil required hospitalization for heart failure, versus 24.4 percent of the rest.

BiDil had substantial side effects — 47.5 percent on it had headaches, compared with 19.2 of the others. Dizziness occurred in 29.3 percent on the drug and 12.3 percent on fake pills.

But the favorable overall result "virtually ensures FDA approval," because the agency previously told the company that a successful study in blacks would merit it, according to Dr. M. Gregg Bloche, a Georgetown University lawyer and Johns Hopkins University physician.

That is "cause for celebration" for blacks, but the company now will have no financial incentive to do a larger trial in whites because its "black-only" patent allows it to sell it that way and keep generic versions from coming the market until 2020, he said.

Others worried that the drug might not be the best choice for every black person, but that they will automatically be prescribed "the black pill" solely on the basis of skin color.

Being black, however, is not a black-and-white distinction, says Dr. Timothy Gardner of the University of Pennsylvania in Philadelphia.

"Physiologically, it's a sort of continuous variable," including people of mixed races, he said.

Dr. Shamir Mehta, a heart expert from McMaster University in Ontario, said genetic differences among ethnic groups are so small that the drug should probably help whites, as well.

Experts, meanwhile, noted that previous studies in the 1980s that found no benefit from the two chemicals in whites were done before modern heart failure drugs were available, and that could warrant a new study involving all races.