Ruxolitinib
Summary
Ruxolitinib is a JAK1/JAK2 inhibitor used primarily to treat myeloproliferative neoplasms, especially myelofibrosis and polycythemia vera resistant to hydroxyurea. It also has an FDA-approved indication for steroid-refractory acute graft-versus-host disease (GVHD) and for moderate-to-severe alopecia areata (as a topical/oral formulation) and vitiligo (topical ruxolitinib, Opzelura). It works by blocking the JAK-STAT signaling pathway, which is often constitutively activated in myeloproliferative disorders due to JAK2 V617F mutation.
Detail
Ruxolitinib inhibits Janus kinase 1 and 2 (JAK1/JAK2), which are tyrosine kinases that mediate signaling from cytokine receptors (e.g., erythropoietin, thrombopoietin, and various interleukin receptors) through the JAK-STAT pathway. In myeloproliferative neoplasms such as primary myelofibrosis, polycythemia vera, and essential thrombocythemia, a gain-of-function mutation in JAK2 (JAK2 V617F) leads to constitutive activation of this pathway, causing excessive proliferation of myeloid cell lines independent of normal growth factor regulation. By inhibiting JAK1/2, ruxolitinib reduces this abnormal signaling, decreasing splenomegaly, constitutional symptoms (fever, night sweats, weight loss), and improving quality of life in myelofibrosis patients, though it does not cure the underlying clonal disease or reliably induce molecular remission.
Key clinical uses: - Intermediate/high-risk myelofibrosis (primary or secondary) to reduce spleen size and symptom burden. - Polycythemia vera resistant/intolerant to hydroxyurea. - Steroid-refractory acute GVHD (oral formulation, FDA-approved 2019). - Topical ruxolitinib (Opzelura) for atopic dermatitis, vitiligo, and nonsegmental vitiligo repigmentation.
Adverse effects: Because JAK1/2 inhibition broadly suppresses hematopoietic cytokine signaling, common side effects include dose-dependent anemia and thrombocytopenia, requiring routine CBC monitoring. Other risks include increased susceptibility to infections (including reactivation of herpes zoster, tuberculosis), and rarely, secondary malignancies (non-melanoma skin cancers) with long-term use. Abrupt discontinuation can cause a rebound inflammatory cytokine release syndrome with fever, hypotension, and rapid splenomegaly recurrence, so tapering is advised.
Mechanistically important for boards: Understanding the JAK-STAT pathway is high-yield for USMIE Step 1, as it links to JAK2 V617F mutation testing in polycythemia vera, essential thrombocythemia, and primary myelofibrosis diagnosis. Ruxolitinib exemplifies targeted molecular therapy contrasting with older cytoreductive agents (hydroxyurea, anagrelide, interferon-alpha).
Sources
- First Aid for the USMLE Step 1 (Myeloproliferative Neoplasms section)
- Katzung's Basic & Clinical Pharmacology
- UpToDate: Ruxolitinib - Drug information
- NCCN Guidelines for Myeloproliferative Neoplasms
- FDA Prescribing Information for Jakafi (ruxolitinib) and Opzelura
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