Moving swiftly and dramatically, the Food and Drug Administration on Thursday approved a drug for treating congestive heart failure in African-Americans.

The agency acted just a week after an FDA advisory committee unanimously endorsed BiDil made by NitroMed ( NTMD) of Lexington, Mass. Seven of the advisers supported the drug for African-Americans, while two said it should be approved for everyone.

The drama in the agency's decision was whether it would approve the drug for a specific ethnic group based on tests that showed BiDil had a significant benefit for African-Americans. Two previous clinical trials among a broader group of patients were inconclusive, but the data suggested that African-Americans could benefit from the drug.

The agency said Thursday after markets had closed that its action represented "a step toward the promise of personalized medicine."

NitroMed's application relied heavily on a clinical trial known as the African-American Heart Failure Trial, or A-HeFT. The study included 1,050 self-identified black patients with severe heart failure "who had already been treated with the best available therapy," the agency said.

A-HeFT results showed that BiDil patients had a 43% reduction in death and a 39% decrease in hospitalization for heart failure vs. patients taking a placebo. The trial was halted last year by an independent medical monitoring board, which said the results were so strong that the placebo patients shouldn't be denied BiDil.

"Today's approval of a drug to treat severe heart failure in self-identified black population is a striking example of how a treatment can benefit some patients even if it does not help all patients," said Dr. Robert Temple, FDA's associate director of medical policy, in a prepared statement.

"The information presented to the FDA clearly showed that blacks suffering from heart failure will now have an additional safe and effective option for treating their condition," he added. "In the future, we hope to discover characteristics that identify people of any race who might be helped by Bidil."

The FDA's approval specifically mentioning BiDil for African-Americans should help NitroMed's efforts to protect its patent on the drug that combines two generic products -- hydralazine, for high blood pressure, and isosorbide dinitrate, for chest pains associated with heart disease.

Analysts had speculated that FDA approval of BiDil for the general population could have made the drug vulnerable to generic competition as early as 2007. NitroMed has two patents, expiring in 2020, relating to BiDil's treatment of African-Americans. A broader patent expires in 2007.

NitroMed's stock lost 72 cents, or 3.7%, to $18.97 in regular trading Thursday. After-hours, shares gained 83 cents, or 4.4%, to $19.80.