Study to Evaluate the Efficacy and Safety of Oral Difelikefalin for Moderate to Severe Pruritus in Subjects With Notalgia Paresthetica

Part A of this study will evaluate the benefit-risk of 3 doses of difelikefalin compared to placebo. The dose with the best benefit-risk profile will be further evaluated in Part B. Part A of this study comprises a 28-day Screening Period, a 7-day Run-in Period, an 8-week Double-blind Treatment Period, a 2-week Treatment Discontinuation Period, and a Safety Follow-up Visit (14 days after the last dose of study treatment). Part B of this study will evaluate the efficacy, safety, and tolerability of oral difelikefalin. The dose of oral difelikefalin to be assessed in Part B will depend on the results of Part A. Part B of this study comprises a 28-day Screening Period, a 7-day Run-in Period, an 8-week Double-blind Treatment Period, up to a 52-week OLE Period, and a Safety Follow-up Visit. Subjects who participated in Part A of the study may not participate in Part B. All subjects will sign an informed consent form (ICF) and undergo screening for study eligibility.