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Trade namesVonjo, Enpaxiq
Other namesSB1518
  • (16E)-11-[2-(1-Pyrrolidinyl)ethoxy]-14,19-dioxa-5,7,26-triazatetracyclo[,6.18,12]heptacosa-1(25),2(26),3,5,8,10,12(27),16,21,23-decaene
Clinical data
Main usesMyelofibrosis[1]
Side effectsDiarrhea, low platelets, nausea, low hemoglobin, swollen legs[1]
Routes of
By mouth
Typical dose200 mg BID[1]
External links
License data
Legal status
Chemical and physical data
Molar mass472.589 g·mol−1
3D model (JSmol)
  • c1cc2cc(c1)-c3ccnc(n3)Nc4ccc(c(c4)COC/C=C/COC2)OCCN5CCCC5
  • InChI=1S/C28H32N4O3/c1-2-13-32(12-1)14-17-35-27-9-8-25-19-24(27)21-34-16-4-3-15-33-20-22-6-5-7-23(18-22)26-10-11-29-28(30-25)31-26/h3-11,18-19H,1-2,12-17,20-21H2,(H,29,30,31)/b4-3+

Pacritinib, sold under the brand name Vonjo, is an medication used to treat myelofibrosis.[1] Specifically it is used in those with a platelet count less than 50 × 109/L in who it decreases the size of the spleen.[1] It is taken by mouth.[1]

Common side effects include diarrhea, low platelets, nausea, low hemoglobin, and swollen legs.[1] Other side effects may include bleeding, prolonged QT, deep vein thrombosis, cancer, and infection.[1] Use is not recommended in those with significant liver or kidney problems.[1] It is a kinase inhibitor that blocks the action of Janus kinase 2 (JAK2) and fms-like tyrosine kinase 3\CD135 (FLT3).[3]

Pacritinib was approved for medical use in the United States in 2022.[1] Its application for approval in Europe was withdrawn in 2017 due to concerns it worsened outcomes.[3] In the United States a month of medication costs about 23,000 USD as of 2022.[4]

Medical uses

Pacritinib in indicated to treat adults who have a rare form of a bone marrow disorder known as intermediate or high-risk primary or secondary myelofibrosis and who have platelet (blood clotting cells) levels below 50,000/µL.[1][2]


It is taken at a dose of 200 mg twice per day.[1]

Mechanism of action

Inhibitory effects of pacritinib in the FMS-like tyrosine kinase and Janus kinase[5]

In terms of the mode of action we find that Pacritinib works by blocking specific proteins that signal cancer cells to multiply and spread. Specifically Pacritinib inhibits wild-type JAK2, mutant JAK2 V617F, and FMS-like tyrosine kinase 3; though it has a greater inhibitory efficacy towards JAK2.[5][6]


The effectiveness and safety of pacritinib were demonstrated in a study that included 63 participants with intermediate or high-risk primary or secondary myelofibrosis and low platelets who received pacritinib 200 mg twice daily or standard treatment.[2] Effectiveness was determined based upon the proportion of participants who had a 35% or greater spleen volume reduction from baseline to week 24.[2] Nine participants (29%) in the pacritinib treatment group had a 35% or greater spleen volume reduction, compared to one participant (3%) in the standard treatment group.[2]

The U.S. Food and Drug Administration (FDA) granted the application for pacritinib priority review, fast track, and orphan drug designations.[2]

Society and culture


Pacritinib is the International nonproprietary name (INN).[7][8]


  1. 1.00 1.01 1.02 1.03 1.04 1.05 1.06 1.07 1.08 1.09 1.10 1.11 1.12 "Vonjo- pacritinib capsule". DailyMed. 7 March 2022. Archived from the original on 24 March 2022. Retrieved 24 March 2022.
  2. 2.0 2.1 2.2 2.3 2.4 2.5 "FDA approves drug for adults with rare form of bone marrow disorder". U.S. Food and Drug Administration. 1 March 2022. Archived from the original on 3 March 2022. Retrieved 3 March 2022. Public Domain This article incorporates text from this source, which is in the public domain.
  3. 3.0 3.1 "Enpaxiq: Withdrawal of the marketing authorisation application". Archived from the original on 4 August 2020. Retrieved 11 December 2022.
  4. "Vonjo Prices, Coupons, Copay & Patient Assistance". Retrieved 11 December 2022.
  5. 5.0 5.1 Hatzimichael, Eleftheria; Tsolas, Evangelos; Briasoulis, Evangelos (19 August 2014). "Profile of pacritinib and its potential in the treatment of hematologic disorders". Journal of Blood Medicine. 5: 143–152. doi:10.2147/JBM.S51253. Archived from the original on 6 August 2022. Retrieved 1 June 2024.
  6. Mascarenhas, John (August 2022). "Pacritinib for the treatment of patients with myelofibrosis and thrombocytopenia". Expert Review of Hematology. 15 (8): 671–684. doi:10.1080/17474086.2022.2112565. ISSN 1747-4094. Archived from the original on 7 May 2023. Retrieved 1 June 2024.
  7. World Health Organization (2010). "International nonproprietary names for pharmaceutical substances (INN). proposed INN: list 104" (PDF). WHO Drug Information. 24 (4): 386. hdl:10665/74579. Archived (PDF) from the original on 2020-07-15. Retrieved 2022-10-13.
  8. World Health Organization (2011). "International nonproprietary names for pharmaceutical substances (INN): recommended INN: list 66". WHO Drug Information. 25 (3). hdl:10665/74683.

External links

External sites: