The Food and Drug Administration has approved the first drug treatment for a rare bone marrow disease, giving the go-ahead for a daily pill called Jakafi to be marketed by the Delaware-based drugmaker Incyte.

The pill, to be taken twice a day, will be used in the treatment of myelofibrosis, a disease that causes swelling of the spleen, pain, fatigue, and anemia because of a buildup in abnormal red blood cells in bone marrow. The disease is now treated with bone marrow transplants or chemotherapy. In some cases, however, patients cannot be treated at all, and Jakafi may provide a way to help more people suffering from the rare disorder.

In a statement hailing the FDA decision, Incyte officials noted that Jakafi (known generically as ruxolitinib) “is the first and only product to be approved by the FDA for myelofibrosis, and the first in a new class of drugs, known as JAK inhibitors, to be approved for any indication.”

“The availability of Jakafi is a significant medical advancement for people living with myelofibrosis, a debilitating disease,” said Dr. Paul A. Friedman, Incyte president and chief executive officer. “This milestone marks a tremendous achievement for Incyte because a scientific discovery from our research laboratories has become the first JAK inhibitor to reach the market and provide a clinical benefit to patients.”

According to Incyte, the bone marrow disease affects some 16,000 to 18,500 people in the United States. Company officials said it’s cost is expected to run about $84,000 a year for patients with insurance coverage But Incyte said it plans to provide co-pay assistance for patients in poor financial shape, and will likely provide it free to uninsured patients.

The drug was approved Wednesday under the FDA’s stepped up review program, designed to produce a decision within six months of a request being submitted. The approval was based, according to the Incyte statement, on two trials involving 528 patients that indicated a “significant” reduction in the swelling of the spleen and a 50 percent improvement in other symptoms associated with myelofibrosis.

Incyte plans to begin marketing the drug next week in partnership with Swiss drugmaker Novartis, which will handle sales abroad.