This is a multicenter, randomized, double-blind, placebo-controlled study to evaluate the efficacy and safety of twice-daily (BID) oral difelikefalin (CR845) in adult subjects with notalgia paresthetica and moderate to severe pruritus.

The study will consist of a 37-day Screening period, a 7-day Run-In period, a 8-week Placebo-Controlled Treatment period followed by a 4-week Active Extension period and a Follow Up visit approximately 14 days after the last dose of study drug.

All subjects will sign an informed consent form (ICF) and undergo screening for study eligibility.

Subjects will be randomized to receive either placebo or difelikefalin (CR845) tablets at a dose of 2.0 mg, orally BID. Intake of the first dose of study drug will be at Day 1.

Subjects who complete the Placebo-Controlled Treatment period of the study will transition into the Active Extension period upon completion of the Week 8 visit assessments. All subjects in the Active Extension will receive difelikefalin (CR845).

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.