Ruxolitinib (brand name: Jakafi) is an oral medication that is used to treat Polycythemia Vera (PV) and Myelofibrosis (MF). Ruxolitinib acts by blocking signaling proteins called janus kinases 1 and 2 (JAK1 and JAK2). These JAK proteins are important for blood forming cells to grow and mature. In MPNs, excess, unregulated signals are transmitted to blood forming cells through these JAK kinases. These extra signals result from mutations in JAK2 (e.g., JAK2V617F) or because of mutations that cause excess activation of normal JAK2 (CALR and MPL mutations). These extra signals disturb the normal controls that regulate blood cell production and, as a result, excess, unneeded blood cells are produced because of the excess JAK signaling. Ruxolitinib blocks some of this excess signaling and can help limit excess blood cell production. Ruxolitinib can also reduce some of the extra cytokines that are produced in patients with MPNs. Reducing cytokine levels can make people feel better. Ruxolitinib can also normalize spleen size in MPN patients.

Ruxolitinib is the first and only FDA-approved drug that is used to treat myeloproliferative neoplasms where hydroxyurea either failed or was not an option. Ruxolitinib is taken by mouth twice a day. 

Side Effects

Ruxolitinib is generally well tolerated but can have significant side effects.

Common side effects are:

  • Low blood counts
  • Infection
  • Skin cancers
  • Increases in cholesterol
  • Bruising
  • Dizziness
  • Headache

Richard T. Silver MD Myeloproliferative Neoplasms Center 525 East 70th St., Starr Pavillion, 3rd Floor New York, NY 10021