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Pharmacology · JAK inhibitors

Ruxolitinib !

An oral JAK1/JAK2 inhibitor for myelofibrosis, polycythaemia vera and graft-versus-host disease. Blood counts and infections are watched.

Updated 2026-11-01

  • Class: JAK inhibitors
  • Enzyme: Janus kinases JAK1 and JAK2
  • ATC code: L01EJ01

The figure shows the human JAK2 kinase domain with ruxolitinib in its ATP site.

Target in 3D: Janus kinases JAK1 and JAK2. PDB structure 6VGL (RCSB PDB, public domain). View the structure at RCSB PDB

Mechanism of action

In myeloproliferative neoplasms the JAK-STAT pathway is overactive, often because of an activating JAK2 mutation. Ruxolitinib inhibits JAK1 and JAK2, which reduces the uncontrolled growth of marrow cells, shrinks the spleen and eases symptoms driven by inflammatory cytokines. In graft-versus-host disease it damps the donor T-cell attack.

  1. Binds the ATP site of JAK1 and JAK2
  2. Overactive JAK-STAT signalling falls
  3. Less marrow overgrowth; smaller spleen
  4. Fewer cytokine symptoms; calmer GVHD

Pharmacokinetics

Absorption
Oral
Metabolism
Liver, mainly by CYP3A4

Indications

Adverse effects

Common

  • Anaemia, low platelets and low white cells
  • Bruising, dizziness, headache
  • Raised cholesterol

Contraindications

  • Hypersensitivity to ruxolitinib

Key interactions

CYP3A4 inhibitors (e.g. ketoconazole)
Slow its clearance and raise its levels.
CYP3A4 inducers (rifampicin, St John's wort)
Lower its exposure.
Other immunosuppressants
Added infection risk.

What is monitored

  • Blood count before and during treatment
  • Lipids
  • Signs of infection, including shingles and new neurological symptoms
  • Skin checks

Administration and safety

  • Oral tablet or extended-release tablet, with or without food.
  • A cream form exists for skin conditions; it is a different product.

Nursing care

  • Check the blood count before each new course or dose change.
  • Teach to report bleeding, unusual bruising, pale skin or tiredness.
  • Teach to report a painful one-sided rash, worsening weakness, trouble speaking or memory changes.
  • Ask about St John's wort and other herbal products.

Pregnancy and breastfeeding

Human data are limited; the treating team weighs benefits and risks.

Test yourself

Think of the answer, then tap the question to see it.

Why is JAK2 a target in myeloproliferative neoplasms?

Many carry an activating JAK2 mutation that keeps the JAK-STAT pathway switched on.

What is the main laboratory toxicity of ruxolitinib?

Low blood counts: anaemia, thrombocytopenia and neutropenia.

Which transplant complication is treated with ruxolitinib?

Graft-versus-host disease after a stem-cell transplant.

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Educational content on how drugs work; not a prescribing guide and no substitute for a health professional's advice. No doses are given.

Sources: Ruxolitinib: MedlinePlus Drug Information (MedlinePlus (U.S. National Library of Medicine), 2026); Goodman & Gilman's The Pharmacological Basis of Therapeutics, 14th ed., ch. 39 (McGraw Hill, 2023); ATCDDD - ATC/DDD Index (WHO Collaborating Centre for Drug Statistics Methodology, 2026).

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Representative model, for educational purposes only.