The Food and Drug Administration approved the first treatment designed for lupus in half a century Wednesday, a decision that stands to generate billions of dollars over several years for Human Genome Sciences of Rockville (HGSI) and its development partner, GlaxoSmithKline (GSK).

Federal regulators estimate that 300,000 to 1.5 million Americans have systemic lupus erythematosus and said in a statement that Benlysta, when used in conjunction with other drugs, offers a way to combat a particularly difficult disease.

"Benlysta, when used with existing therapies, may be an important new treatment approach for health-care professionals and patients looking to help manage symptoms associated with this disease," said Curtis Rosebraugh, director of the Office of Drug Evaluation II in the FDA's Center for Drug Evaluation and Research.

There is no known cure for lupus, a chronic and often debilitating disease in which the immune system attacks the body's organs. Symptoms such as inflammation, pain and tissue damage are typically treated with steroids and immunosuppressant therapies.

Benlysta reduces the disease's level of activity by inhibiting a bodily protein called the B-lymphocyte stimulator, which at elevated levels can contribute to the creation of autoantibodies. Autoantibodies are the cells that attack otherwise healthy tissue, such as the skin, kidneys, heart and joints.

"We expect to have this novel therapy available to physicians and patients within about two weeks, and our entire organization looks forward to the positive impact we hope this new therapy will have for patients with systemic lupus," chief executive H. Thomas Watkins said Wednesday.

Human Genome Sciences has been ramping up its production of Benlysta and hiring salespeople over the past 18 months in anticipation of the FDA's ruling. Executives said in December that they were prepared to dispatch their sales force across the country if given the green light.

Although approval was expected, it was never a guarantee. The FDA had raised concerns about phase three trial data that had suggested that the drug is less effective in African Americans and that the benefits might languish over time.

The agency restated those concerns in its statement Wednesday, and some analysts said the concerns might affect how the drug is labeled and marketed to patients. Details on the drug's label and pricing were not known; a statement from the company was expected.