The Food and Drug Administration (FDA) approved the first new drug to treat lupus in over 50 years, a milestone that medical experts say could prompt development of other drugs that are even more effective in treating the debilitating immune system disorder.

Known as Benlysta, the injectable drug is designed to relieve flare-ups and pain caused by lupus, a little-understood and potentially fatal ailment in which the body attacks its own tissue and organs.

Biotech drugmaker Human Genome Sciences Inc. spent 15 years developing Benlysta and will co-market it with GlaxoSmithKline PLC. The companies estimate there are at least 200,000 lupus patients in theU.S.who could benefit from the drug.

But experts stress that Benlysta is not a miracle drug: It only worked in 35 percent of North American patients tested and was not effective for patients with the deadliest form of the disease. Additionally, it did not show positive results in African Americans, who are disproportionately affected by lupus.

FDA said in its news release it would require the drug developers to conduct another study exclusively in African Americans.

A patient on her anonymity inVirginiastated that she has been taking Benlysta for two years as part of the drug’s clinical trial program. It gave her life back, after being so crushed by pain that she couldn’t take her dog for a walk or drive her children to the school.

FDA approved the drug for systemic lupus erythematosus, the most common form of the disease. Ten-year survival for patients diagnosed with the illness is more than 85 percent, according to the National Institutes of Health (NIH).

Lupus patients have long struggled to draw attention to their disease, which affects women nine times more than men. African Americans are three times more likely to have the disease. Lupus causes fibrous tissue and inflammation of internal organs, skin rashes and joint pain. Most of Benlysta’s benefit came from relieving muscle inflammation versus organ problems, as measured on a comprehensive checklist of lupus symptoms.

The disease occurs when the body’s protector cells, known as antibodies, stop differentiating between foreign invaders, like bacteria, and healthy cells. The cause of this malfunction is not understood.

Currently most patients treat their disease with a variety of drugs that help ease inflammation, including painkillers, steroids and antimalarial drugs — which were first approved for lupus in the 1955. Many patients say there are many side effects of those treatments.

When a mid-stage trial in lupus patients failed to meet researchers’ goals in 2006, many analysts wrote the drug off and downgraded the company’s stock. But when scientists reanalyzed the data they found that the drug helped block the antibodies that cause lupus symptoms in a subset of patients.