WEDNESDAY, Nov. 16 (HealthDay News) -- Jakafi (ruxolitinib) has been approved by the U.S. Food and Drug Administration as the first drug to treat myelofibrosis, a rare disease of the bone marrow, the agency said Wednesday.

In cases of myelofibrosis, healthy bone marrow is replaced by scar tissue, causing blood cells to be made in the liver, spleen and other organs. Symptoms often include an enlarged spleen, anemia, a decrease in white blood cells and platelets, fatigue, abdominal discomfort, pain under the ribs, muscle and bone pain, itching and night sweats, the FDA said in a news release.

Jakafi inhibits the actions of two enzymes that are involved in regulating blood, the agency said. The drug was evaluated in clinical studies involving 528 people, all of whom had an enlarged spleen.

Observed side effects included low blood platelet levels, anemia, fatigue, diarrhea, shortness of breath, headache, dizziness, nausea and confusion.

Jakafi was approved as an orphan drug, since myelofibrosis affects fewer than 200,000 people in the United States, the FDA said.

The drug is produced by Incyte Corp., based in Wilmington, Del.

More information

The FDA has more about this approval.