In Part A of CR845-310601, oral difelikefalin did not demonstrate a meaningful clinical benefit at any dose compared to placebo. The drug was generally well tolerated with a safety profile similar to prior trials.

This is a 2-part, multicenter, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of twice-daily (BID) oral difelikefalin for moderate-to-severe pruritus in adult subjects with NP.

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.

Key Inclusion Criteria:

To be eligible for inclusion into the study, a patient must meet the following criteria:

• Subject has clinically confirmed diagnosis of active Notalgia Paresthetica;
• Subject has a history of chronic pruritus due to Notalgia Paresthetica;
• Subject has moderate to severe pruritus;
• Female subject is not pregnant or nursing during any period of the study.

Key Exclusion Criteria:

A patient will be excluded from the study if any of the following criteria are met:

• Subject has pruritus attributed to a cause other than Notalgia Paresthetica;
• Subject has any clinically significant medical condition or physical/laboratory/ECG/vital signs abnormality that would, in the opinion of the investigator, put the subject at undue risk or interfere with interpretation of study results.