A kinase inhibitor billed as the first treatment specifically for the bone marrow disease myelofibrosis has won approval from the FDA, the agency announced.
The drug is ruxolitinib (Jakafi), an inhibitor of the JAK-1 and JAK-2 enzymes. Dysregulation of these kinases is responsible for myelofibrosis, which causes splenomegaly, anemia, night sweats, and muscle and bone pain.
According to the FDA, the approval was based primarily on two placebo-controlled clinical trials with a total of 528 patients. Patients had failed to respond to conventional therapies and/or were ineligible for bone marrow transplantation. They were randomized to ruxolitinib, placebo, or "best available therapy" consisting of hydroxyurea, chemotherapy agents, or corticosteroids.
More patients receiving ruxolitinib had 35% reductions in spleen volume and 50% declines in clinical symptoms relative to the studies' control groups.
Serious adverse effects seen in the ruxolitinib groups included thrombocytopenia, anemia, fatigue, shortness of breath, headache, dizziness, nausea, and confusion, the FDA said.
A recent study also indicated that serious adverse events may occur when ruxolitinib is stopped. A review of patients receiving the drug at the Mayo Clinic in Rochester, Minn., showed that 11% of patients suffered problems requiring hospitalization during drug discontinuation.
Withdrawal symptoms included acute relapse of myelofibrosis symptoms, rapid and painful enlargement of the spleen, and acute hemodynamic decompensation, which in some patients led to a septic shock-like syndrome.
Ruxolitinib has been designated as an orphan drug, since myelofibrosis is relatively rare and there is no other treatment specifically approved for it.
The drug is manufactured by Incyte of Wilmington, Del.