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

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.