Additional Study Information: The purpose of this study is to test a drug called GSK2330672 that is not yet approved for doctors to prescribe for patients who have a condition called primary biliary cholangitis (PBC) which has caused moderate to severe pruritus, or itching, in parts or all of the body. The objective is to find out if the drug can help to decrease the itchiness that patients are feeling from PBC. This study is about 24 weeks long (about 20 weeks of treatment with GSK2330672 or placebo and about 4 weeks of follow-up without any study treatment). It will look at how people react to GSK2330672 and how the body uses GSK2330672. Participates will need to visit the clinic for 7 study visits to have tests done. Additionally, they will speak on the telephone with a study team member at Week 24 to ask about any changes to their symptoms and treatments as a final Follow-Up to the study. Participants will also be asked to complete questionnaires regarding PBC on an electronic device. In addition to the main study, the study team will also ask patients if they would be willing to participate in two additional optional sub-studies: -Actigraphy Sub-Study -Genetic Substudy