Relieving Chronic Itch: Oral Medication

Inclusion Criteria: * Male and non-pregnant, non-lactating female subjects aged 18 years or older * Diagnosed with chronic idiopathic pruritus (CIP) with an NRS Itch Score of ≥ 7 at both Screening and Baseline * Diagnosis of CIP for at least 6 weeks prior to screening * Willingness to avoid pregnancy or fathering of children * Ability and willingness to provide written informed consent * Willing and able to comply with all study requirements and restrictions * Willing to not participate in any other interventional trial for the duration of their participation * Subjects must be in good health as determined by medical history, physical examination, electrocardiogram, clinical laboratory tests and vital signs * Failure of a course 2-week course of treatment with topical triamcinolone 0.1% ointment BID * Histopathological demonstration of skin dermal edema, eosinophils, mast cell activation or lymphocytic infiltration Exclusion Criteria: 1. Chronic pruritus due to a defined primary dermatologic disorder (e.g., atopic dermatitis, psoriasis, etc.) 2. Patients with a prior diagnosis of excoriation disorder 3. Use of topical treatments for CIP (other than bland emollients) within 1 week of baseline 4. Systemic immunosuppressive or immunomodulating drugs (eg, oral or injectable corticosteroids, methotrexate, cyclosporine, mycophenolat mofetil, azathioprine) within 4 weeks of baseline 5. Subjects with cytopenias at screening, defined as: 1. Leukocytes \< 3 × 109/L 2. Neutrophils \< lower limit of normal 3. Lymphocytes \< 0.8 × 109/L 4. Hemoglobin \< 10 g/dL 5. Platelets \< 100 × 109/L 6. Unwilling or unable to follow medication restrictions or unwilling or unable to sufficiently washout from use of restricted medication 7. Use of any prohibited medications (see Section 5.8) within 14 days or 5 half-lives (whichever is longer) of the baseline visit 8. Current clinically significant cardiovascular, respiratory, neurologic, hepatic, hematopoietic, renal gastrointestinal, endocrine or metabolic dysfunction unless currently controlled and stable, including (but not limited to) the following: 1. Positive for hepatitis C antibody test (anti-HCAbF) with detectable RNA 2. Positive for hepatitis B surface antigen (HBsAg) or hepatitis B core antibody (HBcAb); 3. Positive for HIV (DUO test, p24 antigen) 9. Active malignancy 10. Subjects with a history of malignancy, except for the following adequately treated, nonmetastatic malignancies: basal cell skin cancer, squamous cell carcinomas of the skin, or in situ cervical cancer 11. History (including family history) or current evidence of congenital long QT syndrome or known acquired QT prolongation 12. Exposure to any investigational medication, including placebo, within 60 days of the Baseline Visit 13. History of intolerance and/or hypersensitivity to medications similar to INCB039110 (e.g., Xeljanz) 14. Participation in a previous INCB39110 trial 15. Subjects with severely impaired liver function (Child-Pugh Class C) or end-stage renal disease on dialysis or at least 1 of the following: 1. Serum creatinine \> 1.5 mg/dL; 2. Alanine aminotransferase or aspartate aminotransferase ≥ 1.5 × upper limit of normal 16. Anyone affiliated with the site or sponsor and/or anyone who may consent under duress 17. Any other sound medical reason as determined by the Investigator including any condition which may lead to an unfavorable risk-benefit of study participation, may interfere with study compliance or may confound study results 18. Subjects taking potent systemic CYP3A4 inhibitors or fluconazole within 2 weeks or 5 half-lives, whichever is longer, before the baseline visit 19. Subjects who have previously received JAK inhibitors, systemic or topical (e.g. ruxolitinib, tofacitinib, baricitinib, filgotinib, lestaurtinib and pacritinib) 20. Women who were pregnant or breastfeeding within 4 months before screening. 21. Current or recent history (\< 30 days before screening and/or \< 45 days before randomization) of a clinically meaningful bacterial, fungal, parasitic, or mycobacterial infection 22. Clinically significant or uncontrolled cardiac disease, including unstable angina, acute myocardial infarction within 6 months from Day 1 of study drug administration, New York Heart Association Class III or IV congestive heart failure, and arrhythmia requiring therapy or uncontrolled hypertension (blood pressure \> 150/90 mmHg) unless approved by medical monitor/sponsor 23. History of alcoholism or drug addiction within 1 year before screening, or current alcohol or drug use that, in the opinion of the investigator, will interfere with the subject's ability to comply with the administration schedule and study assessments 24. Subjects who have received systemic chemotherapy at any time 25. Subjects who anticipate receiving a live or live-attenuated vaccination from screening through the final follow-up visit 26. Subjects who, in the opinion of the investigator, are unable or unlikely to comply with the administration schedule and study evaluations \-