 The primary efficacy variable is change from baseline in weekly itch severity score ISS7 at Week 12. The daily itch score is the average of the morning and evening itch severity scores. The baseline ISS7 is the sum of the daily itch severity scores over the 7 days prior to t he randomization Day 1 visit, and the ISS7 at Week 12 is the sum of daily itch scores over the 7 days prior to the Week 12 visit. 