ruxolitinib
Jakafi (ruxolitinib) is a Janus kinase inhibitor from Incyte that blocks JAK1 and JAK2, calming overactive immune and blood-cell signalling. It treats myelofibrosis, polycythaemia vera, and both acute and chronic graft-versus-host disease when other therapies have not worked.
This page is based on EMA, FDA, MedlinePlus, and NCI prescribing information for ruxolitinib; the mechanism is explained in plain language, and analogies are used only where they stay accurate.
How it works
Explains what the medicine does in the body, not dosing, side effects, or safety.
An analogy
Inside blood and immune cells, JAK1 and JAK2 act like relay stations that pass messages from the cell surface to the nucleus. In diseases like myelofibrosis, the relay gets stuck in the 'on' position — the bone marrow overproduces cells, the spleen enlarges, and inflammation runs high. Ruxolitinib switches the relay off: by blocking JAK1 and JAK2, it quiets the constant signal, shrinks the spleen, and calms the immune attack in graft-versus-host disease.
In simple terms
Ruxolitinib is a tablet that blocks two enzymes inside cells called JAK1 and JAK2. These enzymes carry messages from the cell surface to the DNA, telling the cell to grow, divide, or release inflammatory chemicals. In myelofibrosis and polycythaemia vera, mutated JAK enzymes stay switched on and the bone marrow makes too many blood cells, enlarging the spleen. In graft-versus-host disease, overactive immune cells use the same pathway to attack the patient's tissues. By blocking JAK1 and JAK2, ruxolitinib reduces cell overproduction, shrinks the spleen, and dampens harmful immune activity.
In depth
Ruxolitinib is an orally bioavailable inhibitor of Janus-associated kinases 1 and 2 (JAK1, JAK2). The JAK-STAT pathway transmits signals from more than 50 cytokines and growth factors: ligand binding to cell-surface receptors activates receptor-associated JAKs, which phosphorylate the receptor and create docking sites for STAT proteins; STATs are then phosphorylated, dimerise, and translocate to the nucleus to drive gene expression. In myeloproliferative neoplasms, the JAK2 V617F mutation (or, less commonly, MPL or CALR mutations that converge on JAK-STAT activation) causes constitutive signalling and unchecked haematopoiesis. Ruxolitinib binds the ATP-binding site of JAK1 and JAK2, suppressing this pathway, reducing splenomegaly, and lowering circulating pro-inflammatory cytokines. In graft-versus-host disease, it dampens donor T-cell and NK-cell activation driven by IL-6, IL-2, and other JAK-dependent cytokines.
See it in motion
A schematic animation of the mechanism — simplified for clarity, not drawn to scale.
How ruxolitinib inhibits JAK1 and JAK2
- Inside blood and immune cells, JAK1 and JAK2 act like relay stations that pass messages from the cell surface to the nucleus.
- Ruxolitinib is an orally bioavailable inhibitor of Janus-associated kinases 1 and 2 (JAK1, JAK2).
- In myeloproliferative neoplasms, the JAK2 V617F mutation (or, less commonly, MPL or CALR mutations that converge on JAK-STAT activation) causes constitutive signalling and unchecked haematopoiesis.
- Ruxolitinib binds the ATP-binding site of JAK1 and JAK2, suppressing this pathway, reducing splenomegaly, and lowering circulating pro-inflammatory cytokines.
Target: JAK1 and JAK2
Cytoplasmic tyrosine kinases that relay signals from cytokine and growth-factor receptors to the nucleus via the STAT pathway; JAK1 and JAK2 drive haematopoiesis and immune-cell activation, and their overactivity underlies myeloproliferative neoplasms and graft-versus-host disease.
Approved uses
Approved uses differ by country and change over time. Always follow your local prescribing information.
Approved uses in European Union
EMA- Treatment of disease-related splenomegaly or symptoms in adult patients with primary myelofibrosis, post-polycythaemia vera myelofibrosis, or post-essential thrombocythaemia myelofibrosis
- Treatment of adult patients with polycythaemia vera who are resistant to or intolerant of hydroxyurea
- Treatment of adults and paediatric patients aged 28 days and older with acute graft-versus-host disease who have inadequate response to corticosteroids or other systemic therapies
- Treatment of adults and paediatric patients aged 6 months and older with chronic graft-versus-host disease who have inadequate response to corticosteroids or other systemic therapies
Approved uses in United States
FDA- Intermediate or high-risk myelofibrosis, including primary myelofibrosis, post-polycythaemia vera myelofibrosis, and post-essential thrombocythaemia myelofibrosis in adults
- Polycythaemia vera in adults who have had an inadequate response to or are intolerant of hydroxyurea
- Steroid-refractory acute graft-versus-host disease in adult and paediatric patients 12 years and older
- Chronic graft-versus-host disease after failure of one or two lines of systemic therapy in adult and paediatric patients 12 years and older
Approved uses in United States
MedlinePlus- Myelofibrosis (a cancer of the bone marrow in which the bone marrow is replaced by scar tissue and causes decreased blood cell production)
- Polycythaemia vera (a slow growing cancer of the blood in which the bone marrow makes too many red blood cells)
- Acute graft-versus-host disease (a complication of hematopoietic stem-cell transplant that usually develops within the first months after transplant)
- Chronic graft-versus-host disease (a complication of transplant that usually develops at least 3 months after transplant)
Approved uses in United States
NCI- An orally bioavailable Janus-associated kinase (JAK) inhibitor that specifically binds to and inhibits protein tyrosine kinases JAK1 and JAK2, leading to a reduction in inflammation and an inhibition of cellular proliferation via the JAK-STAT pathway
Official sources
The statements on this page trace back to these records.
- Jakavi (ruxolitinib) — Summary of product characteristics and package leaflet, English version
European Medicines Agency
- U.S. Food and Drug Administration: JAKAFI prescribing information
U.S. Food and Drug Administration
- MedlinePlus: ruxolitinib
MedlinePlus, U.S. National Library of Medicine
- National Cancer Institute: ruxolitinib phosphate
National Cancer Institute
This page explains how the medicine works — it isn’t the patient leaflet. For anything that applies to you, read the leaflet that came with your medicine or ask your pharmacist.
MedUnfold provides educational content and is not medical advice. Always follow your local prescribing information and healthcare professional.