1. Pregnant or breastfeeding women, or subjects (male or female) unwilling to take appropriate measures to avoid pregnancy.
2. Subjects with inadequate liver or renal function at screening as demonstrated by any of the following:
c. Encephalopathy ≥ Grade 2 as per Child-Pugh System
d. Hepatocellular disease
e. Total bilirubin > 2 . the upper limit of normal (ULN; unless direct bilirubin is < 2 . ULN)
f. Alanine aminotransferase (ALT) > 2.5 . ULN
g. Modification of Diet in Renal Disease estimated glomerular filtration rate < 30 mL/min/1.73 m2, or requiring dialysis
3. Subjects with PLT count < 100 . 109/L or an ANC of < 1 . 109/L
4. Subjects with impairment of GI function or active GI disease that may significantly alter absorption of ruxolitinib (eg, active ulcerative diseases, uncontrolled nausea, vomiting, diarrhea, malabsorption syndrome, and small bowel obstruction).
5. Subjects with clinically significant bacterial, fungal, parasitic, mycobacterial, or viral infection that requires therapy:
a. Subjects with acute bacterial infections requiring antibiotic use should delay screening/enrollment until the course of antibiotic therapy has been completed.
b. Subjects with known active hepatitis A, B, or C at screening or with known HIV positivity.
6. Subjects with peripheral blood blast count of > 0% at screening.
7. Subjects with an active malignancy over the previous 2 years except treated cervical intraepithelial neoplasia, basal cell carcinoma of the skin, squamous cell carcinoma of the skin, or completely resected papillary thyroid and follicular thyroid cancers.
8. Subjects with clinically significant cardiac disease (Class III or IV) as defined by the New York Heart Association.
9. Subjects receiving therapy for PV other than HU or aspirin within 12 weeks before screening or having a history of 32P therapy.
10. Subjects being treated concurrently with a potent systemic inhibitor of CYP3A4 at the time of screening.
11. Subjects being treated concurrently with any prohibited medications
12. Subjects who have previously received treatment with a JAK inhibitor.
13. Subjects being treated concurrently with any investigational agent or prior participation in an investigational study within 30 days before the first dose of study drug or within 5 half-lives of the investigational product, whichever is longer.
14. Subjects who are unable to comprehend or are unwilling to sign an ICF.
15. Subjects with active alcohol or drug addiction that would interfere with their ability to comply with the study requirements.
16. Subjects with an uncontrolled intercurrent illness or any concurrent condition that, in the investigator’s opinion, would jeopardize the safety of the subject or compliance with the protocol.